Here we report a significant step towards satellite based quantum communication by transmitting an entangled photon over a distance of 144 km between the Canary Islands of La Palma and Tenerife via an optical free-space link. The transmitted photon was received in the Optical Ground Station of the European Space Agency, and the entangled partner photon was detected locally at the transmitter. We have succeeded in establishing quantum correlations under experimental constraints and conditions characteristic for a Space-to-ground experiment. This includes link efficiency requiring a high flux entangled photon source, atmospheric effects, active controlled compact transmitting telescope and an optical Space receiving telescope. The quantum correlations of the transmitted photons with its partner are sufficiently high to violate Bell’s inequality and are also used to generate a quantum cryptographic key. This distance exceeds all previous tests by more than one order of magnitude. The experiment fully exploits the distance limits for ground-based free-space communication, significantly longer distances can only be reached using air- or space-based platforms. The range achieved thereby demonstrates the feasibility of quantum communication in space, involving satellites or the International Space Station (ISS).

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Experimental Demonstration of Free-Space Decoy-State Quantum Key Distribution over 144 km
T. Schmitt-Manderbach, H, Weier, M. Fürst, R. Ursin, F. Tiefenbacher, Th. Scheidl, J. Perdigues, Z. Sodnik, J. G. Rarity, A. Zeilinger, H. Weinfurter,
Phys. Rev. Lett. 98, 010504 (2007) [here]

Entanglement based quantum communication over 144 km
R. Ursin, F. Tiefenbacher, T. Schmitt-Manderbach, H. Weier, T. Scheidl, M. Lindenthal, B. Blauensteiner, T. Jennewein, J. Perdigues, P. Trojek, B. Ömer, M. Fürst, M. Meyenburg, J. Rarity, Z. Sodnik, C. Barbieri, H. Weinfurter, A. Zeilinger
Nature Physics 3, 481 - 486 (2007) [here]

ESA takes steps toward quantum communications