Collective Storage and Retrieval of Photons

We present results on the development of a triggerable single- photon source. Our hybrid experiment takes advantage of collective coupling between a cold ($T\sim10~\mu$K) atomic ensemble of $N=10^4$ Cs atoms and a low finesse optical cavity ($F=1000$.) The combined cavity-ensemble provides a large optical depth $N\eta\sim100$ potentially allowing near unity success rates ($R\sim99\%$) for converting a collective excitation into a photon in a single output mode. In the initial work presented here, we demonstrate excitation storage times of $\sim1~\mu$s, and peak conversion efficiencies of $R\sim30\%$ (and $R\sim70\%$ in more recent work) in the single photon limit. We currently believe that both quantities are limited by doppler decoherence that can be reduced by storing the atoms in a far detuned optical lattice. The quantum-collective nature of the storage and retrieval process is clearly established by observing several phase matching conditions. This work was supported in parts by the NSF, the ARO, and the Sloan Foundation.