Continuous-mode analysis of improved two-way CV-QKD

TL;DR

This paper analyzes an improved two-way continuous-variable quantum key distribution protocol in the continuous-mode regime, incorporating practical device nonidealities, finite-size effects, and demonstrating its robustness and performance advantages over one-way systems.

Contribution

It introduces a continuous-mode security analysis framework for the improved two-way CV-QKD protocol, considering practical nonidealities and finite-size effects.

Findings

The improved two-way protocol maintains a performance advantage over one-way CV-QKD.

The analysis provides practical guidance for implementation and optimization.

The framework accounts for device nonidealities and finite-size effects.

Abstract

Continuous-variable quantum key distribution (CV-QKD) enables information-theoretically secure key generation between legitimate parties. To further enhance system performance, an improved two-way CV-QKD protocol has been proposed, which is accessible in practice and exhibits increased robustness against excess noise. However, in practical implementations, device nonidealities inevitably drive the optical field from the single-mode regime into the continuous-mode regime. In this work, we introduce temporal modes to characterize the evolution of optical fields in the improved two-way protocol and establish a security analysis framework for the continuous-mode scenario based on adaptive normalization with calibrated shot-noise unit. In addition, finite-size effects are taken into account in the analysis. Our results demonstrate that the improved two-way protocol retains a performance advantage over one-way counterpart. The analysis provides useful guidance for the practical implementation and performance optimization of improved two-way CV-QKD systems.