Enhanced continuous-variable quantum key distribution protocol via adaptive signal processing

TL;DR

This paper introduces an adaptive CV-QKD protocol that uses probabilistic filtering to significantly enhance key rates over existing methods, especially in challenging terrestrial and satellite channels, without hardware changes.

Contribution

The authors develop a novel adaptive protocol employing Gaussian and non-Gaussian filters to surpass the performance of the optimal Gaussian CV-QKD protocol, with no hardware modifications.

Findings

Achieved a threefold increase in key rates over GG02 in experiments.

Simulations show a 400-fold increase for satellite communications.

Protocol effectively adapts to rapidly changing channel conditions.

Abstract

Quantum key distribution (QKD) provides a promising approach to secure communications, with continuous-variable QKD (CV-QKD) offering compatibility with existing telecommunication infrastructure. Despite this advantage, CV-QKD is limited by challenges such as losses in terrestrial fibres and atmospheric scintillation in free-space channels. We introduce a QKD protocol that surpasses the optimal Gaussian modulated CV-QKD (GG02) protocol by utilising probabilistic filters without known physical representation. Our approach employs a Gaussian filter at Alice's station and a non-Gaussian notch-like filter at Bob's station. Alice's filter optimises modulation variance to achieve key rates near the optimal GG02 performance, while Bob's filter adapts the effective channel conditions, which can result in higher key rates than the optimal GG02 protocol. Our security analysis avoids Gaussian extremality, accurately bounding Eve's information. The protocol dynamically optimises the secret-key rate for rapidly changing channels, such as terrestrial links and satellite-to-ground communications, and can extract keys in regions deemed non-secure by parameter estimation. Implemented at software level, our protocol requires no hardware modifications and can be integrated into existing QKD systems. Experimental results show a threefold increase in key rates over the optimal GG02 protocol, while simulations for Low Earth Orbit satellite quantum communications indicate a 400-fold increase compared to the non-optimised counterpart.