Generation of narrow-bandwidth single photons using electromagnetically induced transparency in atomic ensembles

We review recent experiments [M. D. Eisaman et al., Nature 438 (2005) 837] demonstrating the generation of narrow-bandwidth single photons using a room-temperature ensemble of Rb-87 atoms. Our method involves creation of an atomic coherence via Raman scattering and projective measurement, followed by the coherent transfer of this atomic coherence onto a single photon using electromagnetically induced transparency (EIT). The single photons generated using this method are shown to have many properties necessary for quantum information protocols, such as narrow bandwidths, directional emission, and controllable pulse shapes. The narrow bandwidths of these single photons (similar to MHz), resulting from their matching to the EIT resonance(similar to MHz), allow them to be stored in narrow-bandwidth quantum memories. We demonstrate this by using dynamic EIT to store and retrieve the single photons in a second ensemble for storage times up to a few microseconds. We also describe recent improvements to the single-photon fedelity compared to the work by M. D. Eisaman in Nature 438 (2005) 837. These techniques may prove useful in quantum information applications such as quantum repeaters, linear-optics quantum computation, and daytime free-space quantum communication.