Storage and Recall of Weak Coherent Optical Pulses with an Efficiency of 25%

We demonstrate experimentally an efficient coherent rephasing scheme for the storage and recall of weak coherent light pulses in an inhomogeneously broadened optical transition in a Pr3+: YSO crystal at 2.1 K. Precise optical pumping using a frequency stable (approximate to 1 kHz linewidth) laser is employed to create a highly controllable atomic frequency comb structure. We report single photon level storage and retrieval efficiencies of 25%, based on coherent photon-echo-type reemission in the forward direction. The high efficiency is mainly a product of our highly controllable and precise ensemble-shaping technique. The coherence property of the quantum memory is proved through interference between a super-Gaussian pulse and the emitted echo.