Optoelectrical cooling of polar molecules to sub-millikelvin temperatures

TL;DR

This paper reports the successful implementation of optoelectrical Sisyphus cooling to bring gaseous formaldehyde molecules into the microkelvin temperature regime, significantly increasing phase-space density and purity of the molecular ensemble.

Contribution

It introduces a simple, dissipative cooling method for electrically trapped dipolar molecules, achieving microkelvin temperatures and high state purity.

Findings

Temperature reduced by three orders of magnitude

Phase-space density increased by a factor of ~$10^4$

Generated ensemble of 3×10^5 molecules at 420 μK

Abstract

We demonstrate direct cooling of gaseous formaldehyde (H2CO) to the microkelvin regime. Our approach, optoelectrical Sisyphus cooling, provides a simple dissipative cooling method applicable to electrically trapped dipolar molecules. By reducing the temperature by three orders of magnitude and increasing the phase-space density by a factor of ~$10^4$ we generate an ensemble of $3\cdot10^5$ molecules with a temperature of about 420\mu K, populating a single rotational state with more than 80% purity.