Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

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

Yanhao Sun, Jiayu Ma, Xiangyu Wang, Song Yu, Ziyang Chen, Hong Guo

TL;DR

The paper develops a temporal-mode, continuous-mode security framework for the improved two-way CV-QKD protocol to address practical device nonidealities. It introduces temporal modes and adaptive shot-noise normalization with calibrated SNU, and treats finite-size effects via CLT and maximum-likelihood bounds, integrating these into a finite-size Covariance-Matrix (FAN) formalism. By constructing both PM and EB pictures and deriving the corresponding covariance matrices, the authors compute secret-key rates using the Holevo bound and mutual information under realistic mode-matching constraints. Numerical results show the improved two-way protocol maintains an advantage over the one-way scheme in terms of tolerable excess noise and maximum transmission distance, even in the presence of finite-size effects, providing practical guidance for implementation and optimization in metropolitan-distance CV-QKD systems. The framework supports future enhancements through better mode matching and DSP strategies to further boost performance.

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.

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

TL;DR

The paper develops a temporal-mode, continuous-mode security framework for the improved two-way CV-QKD protocol to address practical device nonidealities. It introduces temporal modes and adaptive shot-noise normalization with calibrated SNU, and treats finite-size effects via CLT and maximum-likelihood bounds, integrating these into a finite-size Covariance-Matrix (FAN) formalism. By constructing both PM and EB pictures and deriving the corresponding covariance matrices, the authors compute secret-key rates using the Holevo bound and mutual information under realistic mode-matching constraints. Numerical results show the improved two-way protocol maintains an advantage over the one-way scheme in terms of tolerable excess noise and maximum transmission distance, even in the presence of finite-size effects, providing practical guidance for implementation and optimization in metropolitan-distance CV-QKD systems. The framework supports future enhancements through better mode matching and DSP strategies to further boost performance.

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.
Paper Structure (12 sections, 30 equations, 5 figures, 1 table)

This paper contains 12 sections, 30 equations, 5 figures, 1 table.

Table of Contents

  1. Introduction
  2. Continuous-mode Analysis of Improved Two-way QKD
  3. Prepare-and-measure Scheme of the Protocol
  4. Entanglement-based Scheme of the Protocol
  5. Finite-size Effects in the Improved Two-way Protocol
  6. Theoretical Analysis of Finite-Size Effects
  7. Finite-size Statistical Fluctuations
  8. Covariance Matrix in the Ideal Scenario
  9. Finite-size Adaptive Normalization
  10. Method for Calculating the Secret Key Rate
  11. Simulation and Analysis
  12. Conclusions

Figures (5)

  • Figure S1: Prepare-and-measure scheme of the improved two-way protocol in the continuous-mode scenario. $\xi$ denotes a wavepacket that contains the temporal and spectral information.
  • Figure S2: Key equivalence steps between the EB and PM schemes of the protocol. (a) Equivalence at the transmitter. (b) Equivalence at the receiver.
  • Figure S3: Comparison of the protocol performance between the ideal and practical scenarios. The black solid line represents the ideal scenario, while the red dashed line represents the practical scenario.
  • Figure S4: Comparison of the protocol performance between the improved two-way and one-way protocols. The red dashed line represents the improved two-way protocol, while the blue dash-dotted line represents the one-way protocol.
  • Figure S5: Comparison of the most tolerable excess noise between the improved two-way and one-way protocols. The red dashed line represents the improved two-way protocol, while the blue dash-dotted line represents the one-way protocol.