Storage of Single Photons in Atomic Vapor

在这个提议中，我们利用热原子蒸汽中的长寿命相干自旋激发作为光子量子态的存储介质的潜力。这个想法可能会导致在静止（原子）和飞行（光子）量子比特中编码的量子信息之间的接口。通过使用电磁感应透明，133c蒸汽在特定的电子跃迁中失去了不透明性，并伴随着折射率的陡坡。在这种转变中发射的单个光子，将被减慢到每秒几百米的群速度。这些光子既可以通过实验室现有的基于量子点发射的单光子源产生，也可以通过窄带参数下转换产生。在量子信息领域，对单光子存储的基本兴趣是由量子中继器的理论研究激发的，量子中继器可能有助于增加基于光纤的量子密码系统的通信范围，目前限制在150公里左右。该存储装置的其他应用包括光子到集体原子态的纠缠转移，光子波包的形状控制以及非线性光学实验。

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.