Long-distance free-space quantum key distribution with continuous variables
Abstract
Continuous-variable quantum key distribution (CVQKD) enables remote users to share high-rate and unconditionally secure secret keys while maintaining compatibility with classical optical communication networks and effective resistance against background noise. However, CVQKD experiments have only been demonstrated indoors or over short outdoor distances. Here, by developing channel-fluctuation-independent high-precision manipulation of continuous-variable quantum states, high-accuracy quantum signal acquisition and processing, and high-efficiency free-space acquisition, tracking, and pointing technology, we overcome the excess noise due to atmospheric effects especially in daylight without extra wavelength conversion and spectral filtering, and demonstrate for the first time long-distance free-space quantum key distribution over 7-km inland and 9.6-km maritime atmospheric channels with Gaussian-modulated coherent states. This achieved distribution distance of secure quantum secret keys is well beyond the atmosphere's effective thickness, offering a promising alternative for realizing satellite-based quantum cryptography communication in daylight. Moreover, given that the CVQKD system is naturally compatible with existing ground fiber telecommunication networks, it marks an essential step for realizing integrated air-ground quantum access networks with cross-domain applications.
Cite
@article{arxiv.2507.21546,
title = {Long-distance free-space quantum key distribution with continuous variables},
author = {Tianxiang Zhan and Huasheng Li and Peng Huang and Haoze Chen and Jiaqi Han and Zijing Wu and Hao Fang and Hanwen Yin and Zehao Zhou and Huiting Fu and Feiyu Ji and Piao Tan and Yingming Zhou and Xueqin Jiang and Tao Wang and Jincai Wu and Cheng Ye and Yajun Miao and Wei Qi and Guihua Zeng},
journal= {arXiv preprint arXiv:2507.21546},
year = {2025}
}