Phase-coding quantum-key-distribution system based on Sagnac-Mach-Zehnder interferometers

TL;DR

This paper presents a polarization-insensitive phase-coding QKD system using Sagnac-Mach-Zehnder interferometers, demonstrating high stability, robustness against polarization disturbances, and long-distance secure key distribution in fiber channels.

Contribution

The paper introduces a novel polarization-insensitive QKD system based on Sagnac-Mach-Zehnder interferometers, enhancing stability and robustness in real-world fiber networks.

Findings

Achieved a 0.958% quantum bit error rate

Maintained a secure key rate of 3.68 kbps over 12.6 dB channel

Extended maximum transmission distance beyond 125 km

Abstract

Stability and robustness are important criteria to evaluate the performance of a quantum-key-distribution (QKD) system in real-life applications. However, the inherent birefringence effect of the fiber channel and disturbance caused by the variation of the deployment environment of the QKD system tremendously decreases its performance. To eliminate this adverse impact, we propose a polarization-insensitive phase-coding QKD system based on Sagnac-Mach-Zehnder interferometers. Verified by theoretical analysis and experimental tests, this QKD system is robust against channel polarization disturbance. The robustness and long-term stability of the QKD system is confirmed with a 10-day continuous operation over a 12.6-dB channel, which consists of a 50-km fiber spool and a polarization scrambler (2 rad/s). As a result, an average quantum bit error rate of 0.958% and a sustained secure key rate of 3.68 kbps are obtained. Moreover, the secure key rate of the QKD system for a typical channel loss of 10 dB reaches 6.89 kbps, and the achievable maximum transmission distance exceeds 125 km.