Distributing entanglement and single photons through an intra-city, free-space quantum channel

Author(s): K. J. Resch, H. Weinfurter, H. Weier, P. Walther, R. Ursin, M. Taraba, T. Schmitt-Manderbach, A. Poppe, C. Kurtsiefer, A. Fedrizzi, H. R. Böhm, B. Blauensteiner, M. Lindenthal, A. Zeilinger

Journal: Optics Express

Volume: 13

Page(s): 202-209

Year: 2005

DOI Number: 10.1364/OPEX.13.000202

Link: Link to publication


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±0.019, which violates the CHSH-Bell inequality by 14 standard deviations. This result is promising for entanglement-based freespace 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.

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