Quantum Optics Laboratory

A high-storage efficiency and long-lived quantum memory for photons is an essential component in long-distance quantum communication and optical quantum computation. Here, we report a 78% storage efficiency of light pulses in a cold atomic medium based on the effect of electromagnetically induced transparency. At 50% storage efficiency, we obtain a fractional delay of 74, which is the best up-to-date record. The classical fidelity of the recalled pulse is better than 90% and nearly independent of the storage time, as confirmed by the direct measurement of phase evolution of the output light pulse with a beat-note interferometer. Such excellent phase coherence between the stored and recalled light pulses suggests that the current result may be readily applied to single photon wave packets. Our work significantly advances the technology of electromagnetically induced transparency-based optical memory and may find practical applications in long-distance quantum communication and optical quantum computation. DOI: 10.1103/PhysRevLett.110.083601

We demonstrate a simple method to increase the optical density (OD) of cold atom clouds produced by a magneto-optical trap (MOT). A pair of rectangular anti-Helmholtz coils is used in the MOT to generate the magnetic field that produces the cigar-shaped atom cloud. With 7.2 x 10(8) Rb-87 atoms in the cigar-type MOT, we achieve an OD of 32 as determined by the slow light measurement and this OD is large enough such that the atom cloud can almost contain the entire Gaussian light pulse. Compared to the conventional MOT under the same trapping conditions, the OD is increased by about 2.7 folds by this simple method. In another MOT setup of the cigar-shaped Cs atom cloud, we achieve an OD of 105 as determined by the absorption spectrum of the |6S(1/2), F = 4 > ->| 6P(3/2), F ' = 5 > transition. (C) 2008 Optical Society of America