Practical continuous-variable quantum key distribution using dynamic digital signal processing: security proof and experimental demonstration

TL;DR

This paper develops a security framework for dynamic digital signal processing in continuous-variable quantum key distribution, demonstrating both theoretical analysis and experimental validation to ensure secure high-speed quantum communication.

Contribution

It introduces a new security proof model for dynamic algorithms, addressing the underestimation of excess noise and enabling secure high-speed CV-QKD systems.

Findings

Achieved a secret key rate of 14.4 Mbps experimentally.

Demonstrated conventional algorithms underestimate excess noise.

Validated the security model through experimental results.

Abstract

Digital signal processing technology has paved the way for the realization of high-speed continuous-variable quantum key distribution systems. However, existing security proofs are limited to static digital signal processing algorithms, while practical systems rely on dynamic multiple-input multiple-output algorithms to compensate for time-varying channel impairments. Our analysis reveals that the conventional dynamic algorithm, due to its non-unitary nature, systematically underestimates the excess noise, which in turn leads to security issues and the generation of insecure keys. To close this gap, we propose a secure algorithm model, mapping the dynamic algorithm to an equivalent physical optical model whose security can be rigorously assessed. Simulations illustrate the algorithm's non-unitary property and provide a quantitative analysis of the excess noise underestimation caused by the conventional algorithm. We further experimentally validate the necessity of the proposed modeling for dynamic digital signal processing, achieving a secret key rate of 14.4 Mbps based on estimated excess noise of 0.07 shot noise unit; whereas the conventional algorithm would have dangerously overestimated the key rate to 28.2 Mbps with noise of 0.008 shot noise unit. This work provides the essential security framework for dynamic digital signal processing, overcoming a critical impediment for the development of high-performance continuous-variable quantum key distribution systems.