Storage of Single Photons in Atomic Vapor

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In this proposal we exploit the potential of long-living coherent spin-excitations in hot atomic vapor as a storage medium for photonic quantum states. This idea may lead to an interface between quantum information encoded in stationary (atomic) and flying (photonic) qubits. By use of electromagnetically induced transparency, 133Cs vapor looses its opaqueness for a particular electronic transition, accompanied by a steep slope in the index of refraction. Single photons, emitted on this transition, will be slowed down to group velocities of a few hundred meters per second. These photons can be generated either by a source for single photons based on quantum dot emission existing in our lab or by narrow-bandwidth parametric down-conversion.In the field of quantum information, the fundamental interest in single photon storage is stimulated by theoretical research on quantum repeaters that may help to increase the communication range of fiber-based quantum cryptographic systems limited to about 150 km today. Other applications of this storage device cover entanglement transfer from photons to collective atomic states, shape control of photon wave packets, and experiments in non-linear optics.