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Quantum key distribution (QKD) has the potential to improve communicationssecurity by offering cryptographic keys whose security relies on thefundamental properties of quantum physics. The use of a trusted quantumreceiver on an orbiting satellite is the most practical near-term solution tothe challenge of achieving long-distance (global-scale) QKD, currently limitedto a few hundred kilometers on the ground. This scenario presents uniquechallenges, such as high photon losses and restricted classical datatransmission and processing power due to the limitations of a typical satelliteplatform. Here we demonstrate the feasibility of such a system by implementinga QKD protocol, with optical transmission and full post-processing, in thehigh-loss regime using minimized computing hardware at the receiver. Employingweak coherent pulses with decoy states, we demonstrate the production of securekey bits at up to 56.5 dB of photon loss. We further illustrate the feasibilityof a satellite uplink by generating secure key while experimentally emulatingthe varying channel losses predicted for realistic low-Earth-orbit satellitepasses at 600 km altitude. With a 76 MHz source and including finite-sizeanalysis, we extract 3374 bits of secure key from the best pass. We alsoillustrate the potential benefit of combining multiple passes together: whileone suboptimal "upper-quartile" pass produces no finite-sized key with oursource, the combination of three such passes allows us to extract 165 bits ofsecure key. Alternatively, we find that by increasing the signal rate to 300MHz it would be possible to extract 21570 bits of secure finite-sized key injust a single upper-quartile pass.

Experimental quantum key distribution with simulated ground-to-satellite photon losses and processing limitations