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arXiv · 2503.17744

Free-Space Twin-Field Quantum Key Distribution

Yu-Huai Li·Ting Zeng·Min-Yan Wang·Cong Jiang·Jin Lin·Hao-Bin Fu·Xin-Yang Zheng·Jiu-Peng Chen·Zeng-Sen Lin·Cheng-Lin Li·Jian-Yu Guan·Yang Li·Qi Shen·Hao Li·Lixing You·Zhen Wang·Fei Zhou·Juan Yin·Sheng-Kai Liao·Ji-Gang Ren·Xiang-Bin Wang·Yuan Cao·Qiang Zhang·Cheng-Zhi Peng·Jian-Wei Pan
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Abstract

Twin-field quantum key distribution (TF-QKD) elevates the secure key rate from a linear to a square-root dependence on channel loss while preserving measurement-device-independent security. This protocol is uniquely positioned to enable global-scale quantum networks, even under extreme channel loss. While fiber-based TF-QKD implementations have advanced rapidly since its proposal, free-space realizations have remained elusive due to atmospheric turbulence-induced phase distortions. Here, we report the first experimental demonstration of free-space TF-QKD over 14.2 km urban atmospheric channels, surpassing the effective atmospheric thickness -- a critical threshold for satellite compatibility. We achieve a secret key rate exceeding the repeaterless capacity bound, a milestone for practical quantum communication. Our approach eliminates the need for an auxiliary channel to stabilize a closed interferometer, instead leveraging open-channel time and phase control of optical pulses. This work represents a pivotal advance toward satellite-based global quantum networks, combining high-speed key distribution with inherent resistance to real-world channel fluctuations.

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Yu-Huai Li, Ting Zeng, Min-Yan Wang, Cong Jiang, Jin Lin, Hao-Bin Fu, Xin-Yang Zheng, Jiu-Peng Chen, Zeng-Sen Lin, Cheng-Lin Li, Jian-Yu Guan, Yang Li, Qi Shen, Hao Li, Lixing You, Zhen Wang, Fei Zhou, Juan Yin, Sheng-Kai Liao, Ji-Gang Ren, Xiang-Bin Wang, Yuan Cao, Qiang Zhang, Cheng-Zhi Peng, Jian-Wei Pan. 2025-03-22. Free-Space Twin-Field Quantum Key Distribution. https://doi.org/10.1038/s41566-026-01910-6

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