The quantum internet1 is predicted to be the next-generation information processing platform, promising secure communication2,3 and an exponential speed-up in distributed computation2,4. The distribution of single qubits over large distances via quantum teleportation5 is a key ingredient for realizing such a global platform. By using quantum teleportation, unknown quantum states can be transferred over arbitrary distances to a party whose location is unknown. Since the first experimental demonstrations of quantum teleportation of independent external qubits6, an internal qubit7 and squeezed states8, researchers have progressively extended the communication distance. Usually this occurs without active feed-forward of the classical Bell-state measurement result, which is an essential ingredient in future applications such as communication between quantum computers. The benchmark for a global quantum internet is quantum teleportation of independent qubits over a free-space link whose attenuation corresponds to the path between a satellite and a ground station. Here we report such an experiment, using active feed-forward in real time. The experiment uses two free-space optical links, quantum and classical, over 143 kilometres between the two Canary Islands of La Palma and Tenerife. To achieve this, we combine advanced techniques involving a frequency-uncorrelated polarization-entangled photon pair source, ultra-low-noise single-photon detectors and entanglement-assisted clock synchronization. The average teleported state fidelity is well beyond the classical limit9 of two-thirds. Furthermore, we confirm the quality of the quantum teleportation procedure without feed-forward by complete quantum process tomography. Our experiment verifies the maturity and applicability of such technologies in real-world scenarios, in particular for future satellite-based quantum teleportation.
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We thank the staff of IAC: F. Sanchez-Martinez, A. Alonso, C. Warden, M. Serra and J. Carlos; and the staff of ING: M. Balcells, C. Benn, J. Rey, O. Vaduvescu, A. Chopping, D. González, S. Rodríguez, M. Abreu, L. González; J. Kuusela, E. Wille and Z. Sodnik; and J. Perdigues of the OGS and ESA. X.-S.M., T.J., R.U. and A.Z. thank S. Ramelow for discussions, P. Kolenderski for discussions on the SPDC source with the Bell-state synthesizer, S. Zotter for help during the early stages of the experiment, and R. Steinacker for meteorological advice. J.K. was supported by the EU project MALICIA. E.A. and V.M. thank C. Kurtsiefer and Y.-S. Kim for detector electronics design, J. Skaar for support, and the Research Council of Norway (grant No. 180439/V30) and Industry Canada for support. This work was made possible by grants from the European Space Agency (contract 4000104180/11/NL/AF), the Austrian Science Foundation (FWF) under projects SFB F4008 and CoQuS, and the FFG for the QTS project (no. 828316) within the ASAP 7 program. We also acknowledge support by the European Commission, grant Q-ESSENCE (no. 248095) and the John Templeton Foundation.
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Quantum Information Processing (2018)