Sisyphus Cooling of Polyatomic Molecules

The long-range dipole-dipole interactions between polar molecules and their rich internal structure offer a multitude of experimentally unexplored possibilities for fundamental investigations at ultracold temperatures, ranging from many body physics to quantum information processing. Towards this end, a general approach to cool molecular ensembles akin to laser cooling for alkali atoms has been a much sought-after goal. In this talk, we present the experimental realization of opto-electrical cooling,\footnote{M. Zeppenfeld {\it et al.}, Phys. Rev. A {\bf 80}, 041401 (2009)} a general Sisyphus-type cooling scheme for polar molecules. As a first result, an ensemble of $10^6$ methyl-fluoride molecules has been cooled by more than a factor of 4 to 77mK, resulting in an increase in phase-space density by a factor of 7. The scheme proceeds in an electric trap, and requires only a single infrared laser with additional RF and microwave fields. The cooling cycle depends on generic properties of polar molecules and can thus be extended to a wide range of molecule species. Ongoing improvements in our trap design will allow cooling to sub-mK temperatures and beyond, opening wide-ranging opportunities for fundamental studies with polyatomic molecules at ultracold temperatures.