Reverse-encoded quantum key distribution with Gaussian-modulated coherent states

The continuous-variable quantum key distribution (CVQKD) is of great value in the practical secure quantum cryptography. However, the signal-to-noise ratio (SNR) of the CVQKD scheme can be extremely low under high channel loss, which greatly affects the performance of key reconciliation algorithms in practical systems, resulting in low reconciliation efficiency and high frame error rate, thus making the secret key rate extremely low. Meanwhile, the low SNR puts higher requirements on the signal processing. In this paper, we present a novel reverse-encoded quantum key distribution (RE-QKD) with Gaussian-modulated coherent states (GMCS) where the encoding of raw keys is implemented by the Gaussian modulation at the Bob site instead of the Alice site, which greatly improves the SNR. We build the prepare-and-measure (PM) scheme and entanglement-based (EB) scheme for the RE-QKD protocol and conduct the security analysis under general collective attacks. The simulation results indicate that the proposed protocol can tolerate higher channel loss and excess noise compared with the conventional GMCS-CVQKD protocol. The RE-QKD protocol inherits the advantages of GMCS-CVQKD while reducing difficulties in high-performance reconciliation, facilitating the signal processing, and improving its ability to tolerate the channel loss and the excess noise, which shows its applicability in quantum communication networks.