Distributing entanglement and single photons through an intra-city, free-space quantum channel.
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.
Resch
K
K
Lindenthal
M
M
Blauensteiner
B
B
Böhm
H
H
Fedrizzi
A
A
Kurtsiefer
C
C
Poppe
A
A
Schmitt-Manderbach
T
T
Taraba
M
M
Ursin
R
R
Walther
P
P
Weier
H
H
Weinfurter
H
H
Zeilinger
A
A