We have distributed entangled photons directly through the atmosphere to a receiver station 7.8 km away over the city of Vienna, Austria at night. Detection of one photon from our entangled pairs constitutes a triggered single photon source from the sender. With no direct time-stable connection, the two stations found coincidence counts in the detection events by calculating the cross-correlation of locally-recorded time stamps shared over a public internet channel. For this experiment, our quantum channel was maintained for a total of 40 minutes during which time a coincidence lock found approximately 60000 coincident detection events. The polarization correlations in those events yielded a Bell parameter, S=2.27/pm0.019, which violates the CHSH-Bell inequality by 14 standard deviations. This result is promising for entanglement-based free-space quantum communication in high-density urban areas. It is also encouraging for optical quantum communication between ground stations and satellites since the length of our free-space link exceeds the atmospheric equivalent.
@article{arxiv.quant-ph/0501008,
title = {Distributing entanglement and single photons through an intra-city, free-space quantum channel},
author = {K. J. Resch and M. Lindenthal and B. Blauensteiner and H. R. Boehm and A. Fedrizzi and C. Kurtsiefer and A. Poppe and T. Schmitt-Manderbach and M. Taraba and R. Ursin and P. Walther and H. Weier and H. Weinfurter and A. Zeilinger},
journal= {arXiv preprint arXiv:quant-ph/0501008},
year = {2009}
}
Comments
8 pages including 1 figure and 2 tables. The first two authors contributed equally to this work