Wednesday, January 26, 2005

[1.26.2005] Quantum relays for long distance quantum cryptography

Journal of Modern Optics
Issue: Volume 52, Number 5 / March 20, 2005
Pages: 735 - 753

URL: JMO52.0735, 2005
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DOI: 10.1080/09500340412331283633
Quantum relays for long distance quantum cryptography
Daniel Collins , Nicolas Gisin , Hugues De Riedmatten
A1 Group of Applied Physics University of Geneva 20 rue de l'Ecole-de-M├ędecine CH-1211 Geneva 4 Switzerland
Quantum cryptography is on the verge of commercial application. One of its greatest limitations is over long distance--secret key rates are low and the longest fibre over which any key has been exchanged is currently 100km. We investigate the quantum relay, which can increase the maximum distance at which quantum cryptography is possible. The relay splits the channel into sections and sends a different photon across each section, increasing the signal-to-noise ratio. The photons are linked as in teleportation, with entangled photon pairs and Bell measurements. We show that such a scheme could allow cryptography over hundreds of kilometres with today's detectors. It could not, however, improve the rate of key exchange over distances where the standard single section scheme already works. We also show that reverse key reconciliation, previously used in continuous variable quantum cryptography, gives a secure key over longer distances than forward key reconciliation.


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