Minimization of information leakage in continuous-variable quantum key distribution

TL;DR

This paper analyzes and improves a quantum key distribution protocol by addressing asymmetry issues, ultimately minimizing information leakage to eavesdroppers in pure-loss and noisy channels.

Contribution

It provides an asymptotic security analysis of an asymmetric protocol and introduces a heralding symmetrization method to eliminate information leakage.

Findings

Asymptotic security against general asymmetric attacks is established.

Symmetrization via heralding effectively minimizes information leakage.

The protocol asymptotically eliminates leakage in pure-loss channels.

Abstract

A communication protocol based on a Gaussian modulation of squeezed states in a single quadrature and measured via homodyne detection can completely eliminate information leakage to an eavesdropper in a pure-loss channel. However, the asymmetry of the protocol with respect to the quadratures of light presents security issues and the eavesdropper's information is not necessarily minimized for general asymmetric attacks. Here, we perform asymptotic security analysis of the asymmetric protocol against general asymmetric collective attacks and bound the eavesdropper's information via the Heisenberg uncertainty principle. The bound is not tight and therefore, we symmetrize the protocol in a heralding way, discarding the issues of asymmetry altogether. Our proposed heralding protocol asymptotically eliminates information leakage in a pure-loss channel and minimizes leakage in a noisy channel.