Experimental demonstration of non-bilocality with truly independent sources and strict locality constraints

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Abstract

The ongoing interest in creating a secure global quantum network culminated recently in the demonstration of transcontinental quantum communication1. There is a pressing need to examine the properties attached to a quantum network architecture from multiple perspectives, including physics foundations2, communication security3, the efficient use of resources and innovative technological applications4,5. Here, we present an experimental realization of a five-node quantum network, in which quantum sources at two nodes deliver entangled photon pairs to three measurement nodes. With relevant events between five nodes separated space-like, we demonstrate violation of the Bell inequality and bilocal inequality6, with the locality, measurement independence and quantum source independence loopholes closed simultaneously in a quantum network. This experimental realization may be valuable for the design and implementation of future quantum networks.

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Fig. 1: Space–time diagram of the simplest quantum network.
Fig. 2: Schematics for testing the bilocality in a network.
Fig. 3: Space–time configuration of relevant events in each experimental trial.
Fig. 4: \({\cal{B}}_{13}\) and \(\cal{S}\) versus noise parameter p.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

We thank Y. Liu, Y. Li and Y.-Q. Nie for enlightening discussions, Y.-L. Mao for assistance, K.-X. Yang for help with the aerial photographs and Quantum Ctek for providing the components used in the QRNGs. This work was supported by the National Key R&D Program of China (2017YFA0303900, 2017YFA0304000), the National Natural Science Foundation of China and the Chinese Academy of Sciences.

Author information

Q.-C.S., Q.Z., J.F. and J.-W.P. conceived and designed the experiments. B.B. and J.Z. built the QRNGs. W.Z., H.L., L.Y. and Z.W. fabricated the SNSPDs. Q.-C.S. and Y.-F.J. built the experimental network and carried out the experiment. X.J. and X.C. provided experimental assistance. Q.-C.S. and Y.-F.J. analysed the data. Q.-C.S., Q.Z., J.F. and J.-W.P. wrote the manuscript, with input from all authors.

Correspondence to Qiang Zhang or Jingyun Fan or Jian-Wei Pan.

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