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APS » Journals » Phys. Rev. Lett. » Volume 81 » Issue 17
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Phys. Rev. Lett. 81, 3563–3566 (1998)

Violation of Bell Inequalities by Photons More Than 10 km Apart

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W. Tittel*, J. Brendel, H. Zbinden, and N. Gisin
Group of Applied Physics, University of Geneva, 20, Rue de l'Ecole de Médecine, CH-1211 Geneva 4, Switzerland

Received 10 June 1998; published in the issue dated 26 October 1998

A Franson-type test of Bell inequalities by photons 10.9 km apart is presented. Energy-time entangled photon pairs are measured using two-channel analyzers, leading to a violation of the inequalities by 16 standard deviations without subtracting accidental coincidences. Subtracting them, a two-photon interference visibility of 95.5% is observed, demonstrating that distances up to 10 km have no significant effect on entanglement. This sets quantum cryptography with photon pairs as a practical competitor to the schemes based on weak pulses.

© 1998 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.81.3563
DOI:
10.1103/PhysRevLett.81.3563
PACS:
03.65.Bz, 03.67.Dd, 42.81.-i

*Email address: wolfgang.tittel@physics.unige.ch

 
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