Air to ground quantum key distribution

The range of quantum key distribution (QKD) systems is known to be limited to a few hundreds of km due to the attenuation of the channel and the finite signal to noise ratio of available detectors. Satellite based systems, however, could provide efficient links for global scale QKD. While both classical satellite downlinks and long range terrestrial free-space QKD were shown successfully, a quantum key exchange with a rapidly moving platform is still missing. Here we report on the first experimental demonstration of a BB84 QKD transmission from an airplane at a speed of 290 km/h to ground. Our system uses attenuated laser pulses with a mean photon number of μ = 0.5 and polarization encoding. Over a distance of 20 km a stable link was achieved for 10 min yielding a sifted key rate of 145 bits/s with a quantum bit error rate (QBER) of 4.8 %