\section*{Acknowledgement}
We are grateful to \v{C}. Brukner, M. \.{Z}ukowski, M. Aspelmeyer and N. Langford for helpful discussions as well as to T. Bergmann and G. Mondl for assistance with the electronics. We also wish to thank F. Sanchez (Director IAC) and A. Alonso (IAC), T. Augusteijn, C. Perez and the staff of the Nordic Optical Telescope (NOT), J. Kuusela, Z. Sodnik and J. Perdigues of the Optical Ground Station (OGS) as well as J. Carlos and the staff of the Residence of the Observatorio del Roque de Los Muchachos for their support at the trial sites. We acknowledge support from the European Commission, Project QAP (No.015848), Q-ESSENCE (No. 248095), ERC Senior Grant (QIT4QAD), the Marie-Curie research training network EMALI, and SFB-FOQUS, Templeton Fellowship at the Austrian Academy of Science's Institute for Quantum Optics and Quantum Information Vienna, and the Doctoral Program CoQuS of the Austrian Science Foundation (FWF).


