Entanglement-based quantum communication over 144 km


Quantum entanglement is the main resource to endow the field of quantum information processing with powers that exceed those of classical communication and computation. In view of applications such as quantum cryptography or quantum teleportation, extension of quantum-entanglement-based protocols to global distances is of considerable practical interest. Here we experimentally demonstrate entanglement-based quantum key distribution over 144 km. One photon is measured locally at the Canary Island of La Palma, whereas the other is sent over an optical free-space link to Tenerife, where the Optical Ground Station of the European Space Agency acts as the receiver. This exceeds previous free-space experiments by more than an order of magnitude in distance, and is an essential step towards future satellite-based quantum communication and experimental tests on quantum physics in space.

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Figure 1: The free-space link between the Canary Islands La Palma and Tenerife in a picture taken from a satellite (clouds are shown here).
Figure 2: Complete characterization of the quantum link.
Figure 3: The closed-loop tracking system on La Palma.
Figure 4: Long-term behaviour of the AOA of the tracking beacon on the tracking CCD.
Figure 5: A time series of CCD images of the spot at the APDs illustrates the fluctuations due to atmospheric turbulence.


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The authors wish to thank F. Sanchez (Director IAC) and A. Alonso (IAC), T. Augusteijn and the staff of the Nordic Optical Telescope (NOT) and the staff of the Telescopio Nazionale Galileo (TNG) in La Palma for their support at the trial sites. Furthermore, we thank C. Brukner and J. Kofler for helpful discussions. This work was supported by ESA under the General Studies Programme (QIPS study, ESA contract number 18805/04/NL/HE), the Austrian Science Foundation (FWF) under project number SFB1520, the A8-Quantum information Highway project of the Bavarian High-Tech Initiative, the European projects SECOQC and QAP and the ASAP programme of the Austrian Space Agency (FFG). Additional support was provided by the ESA, the Swiss National Science Foundation (SNF) and the DOC program of the Austrian Academy of Sciences.

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Correspondence to R. Ursin or A. Zeilinger.

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Ursin, R., Tiefenbacher, F., Schmitt-Manderbach, T. et al. Entanglement-based quantum communication over 144 km. Nature Phys 3, 481–486 (2007). https://doi.org/10.1038/nphys629

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