Abstract
Towards realizing the future quantum internet1,2, a pivotal milestone entails the transition from two-node proof-of-principle experiments conducted in laboratories to comprehensive multi-node set-ups on large scales. Here we report the creation of memory–memory entanglement in a multi-node quantum network over a metropolitan area. We use three independent memory nodes, each of which is equipped with an atomic ensemble quantum memory3 that has telecom conversion, together with a photonic server where detection of a single photon heralds the success of entanglement generation. The memory nodes are maximally separated apart for 12.5 kilometres. We actively stabilize the phase variance owing to fibre links and control lasers. We demonstrate concurrent entanglement generation between any two memory nodes. The memory lifetime is longer than the round-trip communication time. Our work provides a metropolitan-scale testbed for the evaluation and exploration of multi-node quantum network protocols and starts a stage of quantum internet research.
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Data availability
Source data for the plots is archived on Zenodo at https://doi.org/10.5281/zenodo.8149009 (ref. 49).
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Acknowledgements
We acknowledge QuantumCTek for the allocation of node Bob, and Hefei Institutes of Physical Science for the allocation of node Charlie. This research was supported by the Innovation Program for Quantum Science and Technology (no. 2021ZD0301104), National Key R&D Program of China (no. 2020YFA0309804), National Natural Science Foundation of China (no. T2125010), Anhui Initiative in Quantum Information Technologies, and the Strategic Priority Research Program of the Chinese Academy of Sciences (no. XDB35000000).
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X.-H.B. and J.-W.P. conceived and designed the research. J.-L.L., X.-Y.L., Y.Y., C.-Y.W., B.W., Z.Y. and D.T. performed the experiment. Y.H., J.-W.J. and X.J. developed the phase feedback electronics. M.-Y.Z., X.-P.X. and Q.Z. built the QFC modules. B.Y., X.-B.L. and Q.-H.M. made a pump laser for the QFC. J.Z. contributed silicon single-photon detectors. J.-L.L., X.-Y.L., Y.Y., X.-H.B. and J.-W.P. analysed the data and wrote the paper with input from all other authors.
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Liu, JL., Luo, XY., Yu, Y. et al. Creation of memory–memory entanglement in a metropolitan quantum network. Nature 629, 579–585 (2024). https://doi.org/10.1038/s41586-024-07308-0
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DOI: https://doi.org/10.1038/s41586-024-07308-0
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