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arXiv · 2508.17940

A Metropolitan-scale Multiplexed Quantum Repeater with Bell Nonlocality

Tian-Xiang Zhu·Chao Zhang·Zhong-Wen Ou·Xiao Liu·Peng-Jun Liang·Xiao-Min Hu·Yun-Feng Huang·Zong-Quan Zhou·Chuan-Feng Li·Guang-Can Guo
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Abstract

Quantum repeaters can overcome exponential photon loss in optical fibers, enabling heralded entanglement between distant quantum memories. The definitive benchmark for this entanglement is Bell nonlocality; however, recent metropolitan-scale demonstrations based on single-photon interference (SPI) schemes have been limited to generating low-quality entanglement, falling short of Bell nonlocality certification. Here, we introduce a multiplexed quantum repeater protocol based on time measurements (MQR-TM), successfully combining the high heralding rate of SPI schemes with the phase robustness of two-photon interference (TPI) schemes. This approach achieves heralded entanglement distribution between two solid-state quantum memories over a record 14.5~km separation, generating a Bell state with a fidelity of $78.6 \pm 2.0\%$. We observe a CHSH-Bell inequality violation by 3.7 standard deviations, marking the first certification of Bell nonlocality in metropolitan-scale quantum repeaters. Our architecture supports autonomous quantum node operation without fiber channel phase stabilization, offering a practical framework for scalable quantum-repeater networks.

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Tian-Xiang Zhu, Chao Zhang, Zhong-Wen Ou, Xiao Liu, Peng-Jun Liang, Xiao-Min Hu, Yun-Feng Huang, Zong-Quan Zhou, Chuan-Feng Li, Guang-Can Guo. 2026-04-15. A Metropolitan-scale Multiplexed Quantum Repeater with Bell Nonlocality. https://doi.org/10.1038/s41566-026-01911-5

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