Sisyphus cooling of electrically trapped polyatomic molecules

A general method of cooling polyatomic molecules to ultracold temperatures is reported; the optoelectrical cooling technique removes kinetic energy via a Sisyphus effect, effectively causing the molecules to continually ‘climb’ a hill of potential energy. Optoelectrical cooling of polar molecules Ultracold polar molecules are of interest for various fundamental studies, including quantum-information science, ultracold chemistry and physics beyond the standard model. However, a general method for cooling polyatomic molecules to ultracold temperatures has been lacking. This paper demonstrates an optoelectrical cooling technique that can reduce the temperature of about a million methyl fluoride (CH 3 F) molecules by a factor of more than ten. The scheme removes kinetic energy by means of a 'Sisyphus effect' that causes the molecules to continually 'climb' a hill of potential energy. In contrast to other cooling mechanisms, it proceeds in a trap, cools in all three dimensions and should work for a large variety of polar molecules. The chip-like trap and guide architecture used in this work are well suited to use in quantum-information processing with cold and ultracold molecules. Polar molecules have a rich internal structure and long-range dipole–dipole interactions, making them useful for quantum-controlled applications and fundamental investigations. Their potential fully unfolds at ultracold temperatures, where various effects are predicted in many-body physics 1 , 2 , quantum information science 3 , 4 , ultracold chemistry 5 , 6 and physics beyond the standard model 7 , 8 . Whereas a wide range of methods to produce cold molecular ensembles have been developed 9 , 10 , 11 , 12 , 13 , the cooling of polyatomic molecules (that is, with three or more atoms) to ultracold temperatures has seemed intractable. Here we report the experimental realization of optoelectrical cooling 14 , a recently proposed cooling and accumulation method for polar molecules. Its key attribute is the removal of a large fraction of a molecule’s kinetic energy in each cycle of the cooling sequence via a Sisyphus effect, allowing cooling with only a few repetitions of the dissipative decay process. We demonstrate the potential of optoelectrical cooling by reducing the temperature of about one million CH 3 F molecules by a factor of 13.5, with the phase-space density increased by a factor of 29 (or a factor of 70 discounting trap losses). In contrast to other cooling mechanisms, our sch