Transferring an unknown quantum state over arbitrary distances is essential for large-scale quantum communication and distributed quantum networks. It can be achieved with the help of long-distance quantum teleportation1,2 and entanglement distribution. The latter is also important for fundamental tests of the laws of quantum mechanics3,4. Although quantum teleportation5,6 and entanglement distribution7,8,9 over moderate distances have been realized using optical fibre links, the huge photon loss and decoherence in fibres necessitate the use of quantum repeaters10 for larger distances. However, the practical realization of quantum repeaters remains experimentally challenging11. Free-space channels, first used for quantum key distribution12,13, offer a more promising approach because photon loss and decoherence are almost negligible in the atmosphere. Furthermore, by using satellites, ultra-long-distance quantum communication and tests of quantum foundations could be achieved on a global scale. Previous experiments have achieved free-space distribution of entangled photon pairs over distances of 600 metres (ref. 14) and 13 kilometres (ref. 15), and transfer of triggered single photons over a 144-kilometre one-link free-space channel16. Most recently, following a modified scheme17, free-space quantum teleportation over 16 kilometres was demonstrated18 with a single pair of entangled photons. Here we report quantum teleportation of independent qubits over a 97-kilometre one-link free-space channel with multi-photon entanglement. An average fidelity of 80.4 ± 0.9 per cent is achieved for six distinct states. Furthermore, we demonstrate entanglement distribution over a two-link channel, in which the entangled photons are separated by 101.8 kilometres. Violation of the Clauser–Horne–Shimony–Holt inequality4 is observed without the locality loophole. Besides being of fundamental interest, our results represent an important step towards a global quantum network. Moreover, the high-frequency and high-accuracy acquiring, pointing and tracking technique developed in our experiment can be directly used for future satellite-based quantum communication and large-scale tests of quantum foundations.
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We are grateful to the staff of the Qinghai Lake National Natural Reserve Utilization Administration Bureau, especially Y.-B. He and Z. Xing, for their support during the experiment. We thank B. Zhao and Y.-J. Deng for discussions, and T. Li for proofreading the manuscript before submission. This work was supported by Chinese Academy of Sciences, National Natural Science Foundation of China and the National Fundamental Research Program (under grant no. 2011CB921300).
This file contains Supplementary Text and Data, Supplementary Figures 1-5 and additional references.
About this article
Quantum Engineering (2019)