Rotational cooling of trapped polyatomic molecules

TL;DR

This paper demonstrates a method to cool the rotational states of trapped methyl fluoride molecules, significantly increasing the population in a specific state, which advances control over molecular internal degrees of freedom for cold molecule applications.

Contribution

The authors develop a rotational-state cooling technique for trapped polyatomic molecules, enabling high population transfer to a single rotational level, which was not previously achieved at this scale.

Findings

Over 70% of molecules in the target rotational state

Achieved translational cooling to ~30mK

Ensembles of about 10^6 molecules in a nearly pure state

Abstract

Controlling the internal degrees of freedom is a key challenge for applications of cold and ultracold molecules. Here, we demonstrate rotational-state cooling of trapped methyl fluoride molecules (CH3F) by optically pumping the population of 16 M-sublevels in the rotational states J=3,4,5, and 6 into a single level. By combining rotational-state cooling with motional cooling, we increase the relative number of molecules in the state J=4, K=3, M=4 from a few percent to over 70%, thereby generating a translationally cold (~30mK) and nearly pure state ensemble of about 10^6 molecules. Our scheme is extendable to larger sets of initial states, other final states and a variety of molecule species, thus paving the way for internal-state control of ever larger molecules.