Near-resonant dark optical lattice with increased occupation
Vladimir Elman, Andreas Hemmerich
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 $2\ifmmode\times\else\texttimes\fi{}{10}^{9}$ rubidium atoms with a temperature of $70\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$ and a density of $5\ifmmode\times\else\texttimes\fi{}{10}^{10}\phantom{\rule{0.3em}{0ex}}\text{atoms}∕{\mathrm{cm}}^{3}$ are prepared in a magneto-optic trap (MOT) and a fraction of $5\ifmmode\times\else\texttimes\fi{}{10}^{7}$ 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 $10\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$ with a typical density of $3\ifmmode\times\else\texttimes\fi{}{10}^{11}\phantom{\rule{0.3em}{0ex}}\text{atoms}∕{\mathrm{cm}}^{3}$. We then apply alternating cycles of free evolution in the FOL and cooling and trapping in the DOL, obtaining a fourfold density increase to $1.2\ifmmode\times\else\texttimes\fi{}{10}^{12}\phantom{\rule{0.3em}{0ex}}\text{atoms}∕{\mathrm{cm}}^{3}$---i.e., 7.5% occupation---while maintaining a temperature of $10\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$. 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 $2.8\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{K}$ and a phase-space density of $1.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$. Despite the increased density, no excess heating or collisional losses are observed.
Physical Review A•Oct 31, 2005•5 citations