Finite-size security of continuous-variable quantum key distribution with imperfect heterodyne measurement

TL;DR

This paper develops a security proof for continuous-variable quantum key distribution that accounts for measurement imperfections, demonstrating how phase imbalances affect secure communication distances and proposing mitigation strategies validated experimentally.

Contribution

It introduces a rigorous finite-size security framework for CVQKD with imperfect heterodyne detection, including experimental validation and mitigation methods.

Findings

Measurement imperfections reduce secure communication distance.

A local transformation improves key rates under imperfections.

Experimental validation confirms theoretical predictions.

Abstract

Continuous-variable quantum key distribution (CVQKD) using coherent states and heterodyne detection enables secure quantum communication based on technology that has large similarities to coherent optical telecommunication. Yet, practical implementations of coherent receivers used in both technologies encounter device imperfections, which for CVQKD are often not addressed in security proofs. Here, we present a theoretical framework that rigorously accounts for imperfect heterodyne measurements arising from phase imbalances in the coherent (heterodyne) receiver. Focusing on collective attacks, we establish a finite-size security proof that reveals how measurement imperfections limit the distance over which a positive key rate is achievable. To mitigate these effects, we propose a local transformation during classical post-processing. We validate our approach experimentally on a CVQKD system with an imperfect coherent receiver, underscoring its potential for scalable, cost-effective CVQKD with photonic integrated receivers in which phase-imbalances naturally appear through manufacturing tolerances.