Increasing the atomic density in a near resonant dark optical lattice

Andreas Hemmerich, Vladimir Elman

Wen-Xiang Guo, Wu-Ming Liu

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.

Christopher R. Monroe

G. Grynberg, J.-Y. Courtois

We present a new type of lattice for trapping cold atoms in nearly-dark states where they weakly interact with light. The periodic potential is obtained with fields in a lin ⊥ lin configuration tuned on the blue side of a J → J transition and in the presence of a uniform static magnetic field. A numerical analysis performed for J = 4 demonstrates the occurrence of very small absorption widths and large populations in the lowest vibrational states. These lattices should be interesting for increasing the atomic density and for observing delocalized atomic wave functions.

Andrew A. Geraci, John E. Kitching