CV-MDI quantum key distribution via satellite

Abstract

In this work we analyze a measurement-device-independent (MDI) protocol to establish continuous-variable (CV) quantum key distribution (QKD) between two ground stations. We assume communication occurs between the ground stations via satellite over two independent atmospheric-fading channels influenced by turbulence-induced beam wandering. In this MDI protocol the measurement device is the satellite itself, and the security of the protocol is analyzed through an equivalent entanglement-based swapping scheme. We quantify the positive impact the fading channels can have on the final quantum key rates, demonstrating how the protocol is able to generate a positive key rate even over high-loss atmospheric channels provided that the maximum transmission coefficient of the channel is sufficiently large. This is somewhat counter-intuitive given that the same outcome is only possible in the low-loss regime for a measurement device centrally positioned in a fiber-optic channel. Our results show that useful space-based quantum key generation rates between two ground stations are possible even when the relay satellite is held by an adversary. The cost in key rate incurred by altering the status of the satellite from trustworthy to untrustworthy is presented.