Air-to-ground quantum communication

Quantum key distribution(1,2) (QKD) is the first commercial application in the new field of quantum information, with first routine applications in government and financial sectors(3) and with successful demonstrations of trusted node networks(4,5). Today, the main goal is efficient long-range key distribution via either quantum repeaters(6) or satellites(7-9), with a view to enabling global secure communication. En route to achieving QKD via satellites, a free-space demonstration of secure key distribution was performed between two ground stations(10), over a distance of 144 km. This scenario is comparable to links between satellites in low Earth orbit and ground stations with respect to both attenuation and fluctuations. However, key exchange with rapidly moving platforms remained to be demonstrated. Here, we prove, for the first time, the feasibility of BB84 QKD between an aeroplane and a ground station. By establishing a stable and low-noise quantum communication channel with the aeroplane moving at 290 km h(-1) at a distance of 20 km-that is, 4 mrad s(-1)-our results are representative of typical communication links to satellites(11) or to high-altitude platforms.