Experimental nested purification for a linear optical quantum repeater


Quantum repeaters1,2,3,4 are essential elements for demonstrating global-scale quantum communication. Over the past few decades, tremendous efforts have been dedicated to implementing a practical quantum repeater5,6,7,8,9,10. However, nested purification1, the backbone of a quantum repeater, remains a challenge because the capacity for successive entanglement manipulation is still absent. Here, we propose and demonstrate an architecture of nested purification using spontaneous parametric downconversion sources11. A heralded entangled photon pair with higher fidelity is successfully purified from two copies of low-fidelity pairs that experience entanglement swapping and noisy channels. By delicately designing the optical circuits, double-pair emission noise is eliminated automatically and the purified state can be used for scalable entanglement connections to extend the communication distance. Combined with a quantum memory, our approach can be applied immediately in the implemention of a practical quantum repeater.

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Fig. 1
Fig. 2: Experimental set-up for nested purification.
Fig. 3: Experimental results.


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This work was supported by the National Natural Science Foundation of China (grants nos. 11274292, 11374284, 11425417, 11521063 and 61625503), the National Fundamental Research Program (grants nos. 2013CB336800 and 2013CB922001) and the Chinese Academy of Sciences.

Author information




B.Z., Y.-A.C. and J.-W.P. conceived and designed the experiments. L.-K.C., P.X. and X.-C.Y. designed and characterized the multiphoton optical circuits. H.-L.Y. and C.L. developed the feedback system. T.X., Z.-D.L., H.L., N.-L.L., L.L., T.Y. and C.-Z.P. provided experimental assistance. L.-K.C., H.-L.Y., P.X., T.X. and Z.D-.L. collected and analysed the data. L.-K.C., X.-C.Y., B.Z., Y.-A.C. and J.-W.P. wrote the manuscript, with input from all authors. N.-L.L., Y.-A.C. and J.-W.P. supervised the project.

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Correspondence to Bo Zhao or Yu-Ao Chen or Jian-Wei Pan.

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Chen, L., Yong, H., Xu, P. et al. Experimental nested purification for a linear optical quantum repeater. Nature Photon 11, 695–699 (2017). https://doi.org/10.1038/s41566-017-0010-6

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