Pulsed energy-time enangled 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 distingui shed 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 optica l fibers, opening the door to few-photon applications of quantum communicat ion over long distances. [S0031-9007(99)08777-3].