Long-distance free-space quantum key distribution in daylight towards inter-satellite communication


In the past, long-distance free-space quantum communication experiments could only be implemented at night. During the daytime, the bright background sunlight prohibits quantum communication in transmission under conditions of high channel loss over long distances. Here, by choosing a working wavelength of 1,550 nm and developing free-space single-mode fibre-coupling technology and ultralow-noise upconversion single-photon detectors, we have overcome the noise due to sunlight and demonstrate free-space quantum key distribution over 53 km during the day. The total channel loss is 48 dB, which is greater than the 40 dB channel loss between the satellite and ground and between low-Earth-orbit satellites. Our system thus demonstrates the feasibility of satellite-based quantum communication in daylight. Moreover, given that our working wavelength is located in the optical telecom band, our system is naturally compatible with ground fibre networks and thus represents an essential step towards a satellite-constellation-based global quantum network.

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Figure 1: Satellite-constellation-based global quantum network.
Figure 2: Birds-eye view of the 53 km QKD experiment in daylight.


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The authors thank Y.-A. Chen, Y. Cao, Y. Liu and Y. Xu for discussions. This work was supported by the National Fundamental Research Program (grant no. 2013CB336800), the ‘Strategic Priority Research Program’ of the Chinese Academy of Sciences (grant no. XDA04030000), the National Natural Science Foundation of China, the Chinese Academy of Sciences and the 10000-Plan of Shandong Province (Taishan Scholars).

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Q.Z., C.-Z.P. and J.-W.P. conceived and designed the experiment. S.-K.L., J.L., W.C., Y.L., Z.-H.L., C.-Z.P. and J.-W.P. designed QKD devices. H.-L.Y., C.L., D.-D.L., B.L., H.D., Y.-H.G., J.-G.R., C.-Z.P. and J.-W.P. developed the SMF coupling technique. G.-L.S., J.-Y.G., J.S.P., M.M.F. and Q.Z. implemented upconversion detectors. S.-K.L., H.-L.Y., S.-Q.Z. and W.-Y.L. designed software. X.-B.W. contributed to the decoy-state analysis. Q.Z., C.-Z.P. and J.-W.P. analysed the data and wrote the manuscript, with input from S.-K.L., H.-L.Y. and C.L. All authors contributed to the data collection, discussed the results, and reviewed the manuscript. C.-Z.P. and J.-W.P. supervised the whole project.

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Correspondence to Qiang Zhang or Cheng-Zhi Peng or Jian-Wei Pan.

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The authors declare no competing financial interests.

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Liao, S., Yong, H., Liu, C. et al. Long-distance free-space quantum key distribution in daylight towards inter-satellite communication. Nature Photon 11, 509–513 (2017). https://doi.org/10.1038/nphoton.2017.116

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