N. Gisin

Quantum key distribution over 67 km with a plug&play system

We present a fibre-optical quantum key distribution system. It works at 1550nm and is based on the plug & play setup. We tested the stability under field conditions using aerial and terrestrial cables and performed a key exchange over 67 km between Geneva and Lausanne.

PULSED ENERGY-TIME ENTANGLED TWIN-PHOTON SOURCE FOR QUANTUM COMMUNICATION

A pulsed source of energy-time entangled photon pairs pumped by a standard laser diode is proposed and demonstrated. The basic states can be distinguished by their time of arrival. This greatly simplifies the realization of 2-photon quantum cryptography, Bell state analyzers, quantum teleportation, dense coding, entanglement swapping, GHZ-states sources, etc. Moreover, the entanglement is well protected during photon propagation in telecom optical fibers, opening the door to few-photon applications of quantum communication over long distances.

Spin Flips and Quantum Information for Antiparallel Spins

We consider two different ways to encode quantum information, by parallel or antiparallel pairs of spins. We find that there is more information in the antiparallel ones. This purely quantum mechanical effect is due to entanglement, not of the states but occurring in the course of the measuring process. We also introduce a range of quantum information processing machines, such as spin flip and anticloning.

Quantum Cryptography and Long Distance Bell Experiments: How to Control Decoherence

Several mechanisms that affect one and two photon coherence in optical fibers and their remedies are discussed. The results axe illustrated on quantum cryptography experiments and on long distance Bell inequality tests.