FSO-QKD protocols under free-space losses and device imperfections: a comparative study

Quantum key distribution (QKD) is a technique to establish a secret key between two parties through a quantum channel. Several QKD protocols have been proposed and implemented over optical fibers or free-space links. The main challenge of operating QKD protocols over a free-space link is free-space losses. In this paper, we have studied and compared the performance of single- and entangled-photon-based QKD protocols by evaluating the quantum bit error rate and secure key rate for terrestrial free-space quantum communication by considering different free-space losses, such as geometrical losses, atmospheric losses as well as device imperfections.