ATMOSPHERIC TURBULENCE IMPACT ON THE CONTINUOUS-VARIABLE QUANTUM KEY DISTRIBUTION WITH SPACE-GROUND OPTICAL LINKS

In the context of the future space-ground optical links and telecommunication networks, the issue of securing the transmission channel using quantum resources is currently under intense investigation in France and around the world. Quantum key distribution is a communication method enabling two parties to share a secret key used to encrypt and decrypt the exchanged messages with information-theoretic (unconditional) security. In our study, we consider a LEO downlink quantum key distribution scenario. After propagation through a turbulent atmospheric channel, the transmitted quantum signal is coupled into a single-mode optical fiber on the ground, to enable coherent detection. The principal advantage of CV-QKD is that it requires standard technological to be implemented. Ultimately, the goal is to extract a secret key from the detected quantum signal. As in classical (i.e. non quantum) optical telecommunication, the turbulence degrades the phase and amplitude of the propagating signal, which hampers the coherent detection of the coupled flux, and will in some way degrade the CV-QKD performance. The use of adaptive optics (AO) techniques have proven to be efficient to mitigate these turbulence-induced effects, that can be disastrous for single-mode fiber coupling. The issue at stake in our study is to assess the impact of atmospheric turbulence and correction by adaptive optics on the QKD performance in terms of key rate (bit/s).