Analysis of Imperfections in Practical Continuous-Variable Quantum Key Distribution

TL;DR

This paper investigates practical imperfections in continuous-variable quantum key distribution, analyzing how real-world deviations from ideal models affect security and proposing methods to mitigate these issues.

Contribution

It provides a detailed analysis of how modulation imperfections, calibration errors, and phase noise impact CV-QKD security, offering practical solutions and insights.

Findings

Discrete modulation approximates Gaussian modulation effectively in practice

Proper calibration of shot noise is crucial for security

Phase noise can be exploited to improve secret key rates

Abstract

As quantum key distribution becomes a mature technology, it appears clearly that some assumptions made in the security proofs cannot be justified in practical implementations. This might open the door to possible side-channel attacks. We examine several discrepancies between theoretical models and experimental setups in the case of continuous-variable quantum key distribution. We study in particular the impact of an imperfect modulation on the security of Gaussian protocols and show that approximating the theoretical Gaussian modulation with a discrete one is sufficient in practice. We also address the issue of properly calibrating the detection setup, and in particular the value of the shot noise. Finally, we consider the influence of phase noise in the preparation stage of the protocol and argue that taking this noise into account can improve the secret key rate because this source of noise is not controlled by the eavesdropper.