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arXiv · 2510.17275

Long-distance distribution of atom-photon entanglement based on a cavity-free cold atomic ensemble

Tian-Yu Wang·Ren-Hui Chen·Yan Li·Ze-Hao Shen·Xiao-Song Fan·Zheng-Bang Ju·Tian-Ci Tang·Xia-Wei Li·Jing-Yuan Peng·Zhi-Yuan Zhou·Wei Zhang·Guang-Can Guo·Bao-Sen Shi
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Abstract

Constructing a quantum memory node with the ability of long-distance atom-photon distribution is the essential task for future quantum networks, enabling distributed quantum computing, quantum cryptography and remote sensing. Here we report the demonstration of a quantum-network node with a simple cavity-free cold atomic ensemble. This node gives an initial retrieval efficiency of approximately 50\% and memory lifetime of 160 $\mu$s for atomic qubits. With the aid of a high-efficiency and polarization-independent quantum frequency conversion (QFC) module, the generated entangled photon in the node at 780-nm wavelength is converted to telecom S band at 1522 nm, enabling atom-photon distribution over long distance. We observe an entanglement fidelity between the atoms and telecom photon exceeding 80\% after photon transmission over 20-km fiber, the remaining infidelity being dominated by atomic decoherence. The low-noise QFC with an external efficiency up to 48.5\% gives a signal-to-noise-ratio of 6.9 for transmitted photons with fiber length up to 100 km, laying the cornerstone for entanglement distribution at a hundred-km level. This result provides a new platform towards the realization of a long-distance quantum network.

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Tian-Yu Wang, Ren-Hui Chen, Yan Li, Ze-Hao Shen, Xiao-Song Fan, Zheng-Bang Ju, Tian-Ci Tang, Xia-Wei Li, Jing-Yuan Peng, Zhi-Yuan Zhou, Wei Zhang, Guang-Can Guo, Bao-Sen Shi. 2025-10-20. Long-distance distribution of atom-photon entanglement based on a cavity-free cold atomic ensemble. https://doi.org/10.1103/fzz2-3xf6

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