Improved Four-state Continuous-variable Quantum Key Distribution with Long Secure Distance

TL;DR

This paper presents an improved four-state CVQKD protocol that allows for accurate parameter estimation without linear channel assumptions, ensuring unconditional security and maintaining high efficiency over long distances.

Contribution

The authors introduce a new four-state CVQKD scheme enabling covariance matrix estimation from experimental data without linear assumptions, enhancing security and practicality.

Findings

Achieves long secure distances with unconditional security.

Enables covariance matrix estimation without linear channel assumption.

Compatible with current technological capabilities.

Abstract

The four-state continuous-variable quantum key distribution (CVQKD) protocol has a long practical secure distance \cite{Leverrier_PRL_2009}, while it has the difficulty of parameter estimation. We propose an improved four-state protocol, where the covariance matrix can be estimated from experimental data without using the linear channel assumption, and thus ensuring its unconditional security in the asymptotical limit. Our new scheme keeps the advantages of high reconciliation efficiency and long secure distance of the four-state protocol, and it can be implemented under current technology.