Characterization of Intensity Correlation via Single-photon Detection in Quantum Key Distribution

TL;DR

This paper introduces a real-time, non-intrusive method to characterize intensity correlations in QKD systems using single-photon detection data, enhancing security analysis without system modification.

Contribution

The proposed method allows direct, real-time characterization of intensity correlations in QKD systems from detection data, avoiding additional classical detectors and enabling standard certification.

Findings

Correlation characterization reduces secure key rate in BB84.

Method successfully applied to Bell-state measurement in MDI QKD.

Enables real-time security assessment without system modification.

Abstract

One of the most significant vulnerabilities in the source unit of quantum key distribution (QKD) is the correlation between quantum states after modulation, which shall be characterized and evaluated for its practical security performance. In this work, we propose a methodology to characterize the intensity correlation according to the single-photon detection results in the measurement unit without modifying the configuration of the QKD system. In contrast to the previous research that employs extra classical optical detector to measure the correlation, our method can directly analyse the detection data generated during the raw key exchange, enabling to characterize the feature of correlation in real-time system operation. The basic method is applied to a BB84 QKD system and the characterized correlation decreases the secure key rate shown by the security proof. Furthermore, the method is extended and applied to characterize the correlation from the result of Bell-state measurement, which demonstrates its applicability to a running full-scheme MDI QKD system. This study provides an approach for standard certification of a QKD system.