3D Raman Sideband Cooling of Cesium Atoms at High Density

We laser cool $5\times {10}^7$ Cs atoms to a spin-polarized phase space density of 1/30, the highest ever obtained by laser cooling. It is achieved by compression and polarization gradient cooling in a 3D far-off-resonant optical lattice, followed by 3D Raman sideband cooling optimized at a density of $1.5\times {10}^{12}\mathrm{atoms}/{\mathrm{cm}}^3$, and adiabatic release. In the lattice, $23\%$ of the sites are occupied, $95\%$ of the atoms are in the lowest energy magnetic sublevel, and $37\%$ are in the lowest 3D vibrational state.