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.