Quantum-scissor amplified continuous-variable quantum key distribution

The recent progress in continuous-variable quantum key distribution (CV-QKD) systems has placed them in a competitive position with their conventional discrete-variable counterparts [1]. In particular, CV-QKD might be the better choice over short distances. When it comes to long distances, however, the story is different. One of the proposed solutions to improve rate-versus-distance performance is to use noiseless linear amplifiers (NLAs) [2], but a realistic analysis that accounts for non-idealities of existing NLAs is missing. One of the most well-known NLAs is based on quantum scissors (QSs) [3], whose ideal operation relies on the single-photon assumption of its inputs. In this study, we report the exact calculation of the secret key rate for the GG02 protocol [4] that is enhanced by a single QS; see Fig. 1(a). We remove the single-photon assumption in the QS modeling and find regimes of operation where QS-assisted GG02 offers advantages over the conventional GG02 system. Our results imply that the region over which rate enhancement is achieved is limited to the regime of long distances.