Experimental Frequency-Comb-Based Mode-Pairing Quantum Key Distribution Beyond the Rate-Loss Limit

TL;DR

This paper introduces a frequency-comb-based MP-QKD system that achieves secret key rates beyond the rate-loss limit over long distances using commercial lasers, simplifying implementation for secure quantum communication.

Contribution

Developed a practical frequency-comb-based MP-QKD system that operates with free-running commercial lasers, surpassing the traditional rate-loss limit over long fiber distances.

Findings

Achieved secret key rates exceeding the rate-loss limit by over 2 times at distances up to 404 km.

Demonstrated the system's robustness and practicality for long-distance secure communication.

Supported cryptographic applications with high secret key rates over 202 km.

Abstract

Mode-pairing quantum key distribution (MP-QKD) offers significant potential for long-distance secure communication, benefiting from its quadratic scaling capacity and phase compensation-free characteristic. However, MP-QKD still requires stringent wavelength consistency between remote lasers, which is impractical with commercial lasers without locking. In this work, we develop a simple optical-frequency-comb-based MP-QKD system to simultaneously establish coherence and distribute keys with free-running commercial lasers. We implement the experiment over standard single-mode fiber with a loss coefficient of 0.2 dB/km. The system achieves finite-size secret key rates (SKRs) of 561.26, 113.59, and 10.20 bits per second over 303.37, 354.62, and 404.25 km, which are 1.0267, 2.5230, and 2.1033 times of the rate-loss limit. Besides, the SKR over 202.31 km is 8695.34 bits per second, which is sufficient to support practical cryptographic applications. These results validate the practicality and robustness of our method, offering a simplified yet high-performance framework for long-distance secure communication.