Laser cooling of cesium atoms in gray optical molasses down to 1.1 μK

We have studied the behavior of cesium atoms cooled in six-beam "gray" optical molasses. Cooling occurs for a laser detuned to the blue side of the $6S_{\frac{1}{2}}$, $F=3\mathrm{}\to 6P_{\frac{3}{2}}$, $F^{\prime }=2\mathrm{}$ transition, and a Sisyphus-type effect accumulates the atoms in states not coupled to the light. We measure a minimum temperature of 1.1±0.1 μK at low atomic density. The typical cooling time is on the order of 1 ms. A linear dependence of the temperature versus atomic density is found with a slope of ∼0.6 μK/(${10}^{10}$ atoms/${\mathrm{cm}}^3$).