High-fidelity transmission of entanglement over a high-loss free-space channel

• Published in: Nature physics Vol. 5; no. 6; pp. 389 - 392
• Main Authors: Fedrizzi, Alessandro, Ursin, Rupert, Herbst, Thomas, Nespoli, Matteo, Prevedel, Robert, Scheidl, Thomas, Tiefenbacher, Felix, Jennewein, Thomas, Zeilinger, Anton
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.06.2009; Nature Publishing Group
• Subjects: Atmospheric attenuation; Atmospheric effects; Atomic; Atoms & subatomic particles; Channel loss; Classical and Continuum Physics; Communication networks; Complex Systems; Condensed Matter Physics; Entangled states; Experiments; letter; Mathematical and Computational Physics; Molecular; Optical and Plasma Physics; Photons; Physics; Physics and Astronomy; Quantum entanglement; Quantum theory; Satellite communications; Satellites; Standard deviation; Theoretical; Turbulence
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys1255

An experiment distributing entangled photons over 144 km significantly raises the bar on distance, channel loss and transmission time—encouraging news with regard to future long-distance quantum-communication networks. Quantum entanglement enables tasks not possible in classical physics. Many quantum communication protocols 1 require the distribution of entangled states between distant parties. Here, we experimentally demonstrate the successful transmission of an entangled photon pair over a 144 km free-space link. The received entangled states have excellent, noise-limited fidelity, even though they are exposed to extreme attenuation dominated by turbulent atmospheric effects. The total channel loss of 64 dB corresponds to the estimated attenuation regime for a two-photon satellite communication scenario. We confirm that the received two-photon states are still highly entangled by violating the Clauser–Horne–Shimony–Holt inequality by more than five standard deviations. From a fundamental point of view, our results show that the photons are subject to virtually no decoherence during their 0.5-ms-long flight through air, which is encouraging for future worldwide quantum communication scenarios.