Comparison of Discrete Variable and Continuous Variable Quantum Key Distribution Protocols with Phase Noise in the Thermal-Loss Channel

TL;DR

This paper compares discrete-variable and continuous-variable quantum key distribution protocols under phase noise in thermal-loss channels, revealing conditions where CV-QKD outperforms DV-QKD in loss tolerance and secret key rate.

Contribution

It provides a detailed analysis of phase noise effects on DV-QKD and CV-QKD, highlighting scenarios where CV-QKD has advantages despite higher noise sensitivity.

Findings

CV-QKD tolerates more loss in low phase noise, high thermal noise regimes

Secret key rate analysis extends regions where CV-QKD outperforms DV-QKD

Phase noise impacts DV-QKD and CV-QKD differently, explaining historical performance differences

Abstract

Discrete-variable (DV) quantum key distribution (QKD) based on single-photon detectors and sources have been successfully deployed for long-range secure key distribution. On the other hand, continuous-variable (CV) quantum key distribution (QKD) based on coherent detectors and sources is currently lagging behind in terms of loss and noise tolerance. An important discerning factor between DV-QKD and CV-QKD is the effect of phase noise, which is known to be more relevant in CV-QKD. In this article, we investigate the effect of phase noise on DV-QKD and CV-QKD protocols, including the six-state protocol and squeezed-state protocol, in a thermal-loss channel but with the assumed availability of perfect sources and detectors. We find that in the low phase noise regime but high thermal noise regime, CV-QKD can tolerate more loss compared to DV-QKD. We also compare the secret key rate as an additional metric for the performance of QKD. Requirements for this quantity to be high vastly extend the regions at which CV-QKD performs better than DV-QKD. Our analysis addresses the questions of how phase noise affects DV-QKD and CV-QKD and why the former has historically performed better in a thermal-loss channel.