title: Quantum teleportation and entanglement distribution over 100-kilometre free-space channels.
abstract: 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 teleportation and entanglement distribution. The latter is also important for fundamental tests of the laws of quantum mechanics. Although quantum teleportation and entanglement distribution over moderate distances have been realized using optical fibre links, the huge photon loss and decoherence in fibres necessitate the use of quantum repeaters for larger distances. However, the practical realization of quantum repeaters remains experimentally challenging. Free-space channels, first used for quantum key distribution, 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 channel. Most recently, following a modified scheme, free-space quantum teleportation over 16 kilometres was demonstrated 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 inequality 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.
authors.affiliation: Shanghai Branch, National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Shanghai 201315, China.
authors.forename: Juan
authors.initials: J
authors.lastname: Yin
authors.forename: Ji-Gang
authors.initials: JG
authors.lastname: Ren
authors.forename: He
authors.initials: H
authors.lastname: Lu
authors.forename: Yuan
authors.initials: Y
authors.lastname: Cao
authors.forename: Hai-Lin
authors.initials: HL
authors.lastname: Yong
authors.forename: Yu-Ping
authors.initials: YP
authors.lastname: Wu
authors.forename: Chang
authors.initials: C
authors.lastname: Liu
authors.forename: Sheng-Kai
authors.initials: SK
authors.lastname: Liao
authors.forename: Fei
authors.initials: F
authors.lastname: Zhou
authors.forename: Yan
authors.initials: Y
authors.lastname: Jiang
authors.forename: Xin-Dong
authors.initials: XD
authors.lastname: Cai
authors.forename: Ping
authors.initials: P
authors.lastname: Xu
authors.forename: Ge-Sheng
authors.initials: GS
authors.lastname: Pan
authors.forename: Jian-Jun
authors.initials: JJ
authors.lastname: Jia
authors.forename: Yong-Mei
authors.initials: YM
authors.lastname: Huang
authors.forename: Hao
authors.initials: H
authors.lastname: Yin
authors.forename: Jian-Yu
authors.initials: JY
authors.lastname: Wang
authors.forename: Yu-Ao
authors.initials: YA
authors.lastname: Chen
authors.forename: Cheng-Zhi
authors.initials: CZ
authors.lastname: Peng
authors.forename: Jian-Wei
authors.initials: JW
authors.lastname: Pan