Near-resonant dark optical lattice with increased occupation

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2005

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A bichromatic near-resonant dark optical lattice (DOL) with rubidium atoms is demonstrated, which provides confinement in the Lamb-Dicke regime in all spatial dimensions. We apply spatially phase-matched optical potentials for each hyperfine ground state in order to enable improved Sisyphus cooling, undisturbed by optical hyperfine pumping processes. We also explore a method to increase the occupation of the DOL. Initially 2×109 rubidium atoms with a temperature of 70μK and a density of 5×1010atoms cm3 are prepared in a magneto-optic trap (MOT) and a fraction of 5×107 atoms is loaded into a far detuned one-dimensional optical lattice (FOL). Subsequently, the MOT is replaced by the DOL, and the atoms become well localized within the microscopic light-shift potentials at a temperature of 10μK with a typical density of 3×1011atoms cm3. We then apply alternating cycles of free evolution in the FOL and cooling and trapping in the DOL, obtaining a fourfold density increase to 1.2×1012atoms cm3-i.e., 7.5% occupation-while maintaining a temperature of 10μK. In a final adiabatic cooling step we reduce the well depth to 75 times the single-photon recoil energy, which leads to a temperature of 2.8μK and a phase-space density of 1.7×10-3. Despite the increased density, no excess heating or collisional losses are observed. © 2005 The American Physical Society.

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