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Friday, September 29, 2000
Physics Building, Room 204
Note special time.
[Host: Simonetta Liuti]
Los Alamos National Laboratories
Quantum cryptography, or more accurately quantum key distribution (QKD),
uses single-photon transmissions to generate the shared, secret random
number sequences, known as cryptographic keys, which are used to encrypt
secret communications. Appealing features of QKD are that its security is
based on principles of quantum physics and attempted eavesdropping can be
detected. (Heisenberg’s uncertainty principle ensures that an adversary can
neither successfully tap the key transmissions, nor evade detection because
eavesdropping raises the key error rate above a threshold value). I shall
describe two quantum cryptography systems, based on the transmission of
non-orthogonal single-photon states to generate shared key material, at Los
Alamos. In one experiment we are generating key material over a 48-kilometer
optical fiber path, and in the other by transmitting photons over a 1.6-km
atmospheric path in daylight. In both cases, key material is built up using
the transmission of a single-photon per bit of an initial secret random
sequence. A quantum-mechanically random subset of this sequence is
identified, becoming the key material after a data reconciliation stage with
the sender. The atmospheric results show that QKD could be used for surface
to satellite transmissions.
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