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.
@article{arxiv.2505.09223,
title = {Experimental Frequency-Comb-Based Mode-Pairing Quantum Key Distribution Beyond the Rate-Loss Limit},
author = {Yi-Fei Lu and Yan-Yang Zhou and Yu-Yao Guo and Xin-Hang Li and Xiao-Lei Jiang and Yang Wang and Yu Zhou and Jia-Ji Li and Chun Zhou and Hong-Wei Li and Lin-Jie Zhou and Wan-Su Bao},
journal= {arXiv preprint arXiv:2505.09223},
year = {2025}
}