Rare earth doped crystals for quantum information devices

Recently, rare earth doped materials have been considered as promising systems in quantum information processing and communication. The most important property used in this field is the ability for a quantum system to be in a superposition state. Such states can be observed for reasonably long times if the microscopic systems are well isolated from their environment and therefore are characterized by a long dephasing time T 2 . Several applications can be considered like quantum cryptography for example. Another application is quantum storage which aims at storing the quantum state of a photon. This is the key to quantum cryptography over long distances.