Sisyphus Laser Cooling of a Polyatomic Molecule

TL;DR

This paper demonstrates magnetically-assisted Sisyphus laser cooling of a polyatomic molecule, SrOH, achieving a significant temperature reduction and paving the way for ultracold polyatomic molecules via direct laser cooling.

Contribution

It introduces a novel laser cooling technique for polyatomic molecules, specifically SrOH, with effective vibrational repumping and substantial temperature reduction.

Findings

Transverse temperature reduced to ~700 μK

Achieved two orders of magnitude cooling in one dimension

Demonstrated vibrational repumping for polyatomic molecules

Abstract

We perform magnetically-assisted Sisyphus laser cooling of the triatomic free radical strontium monohydroxide (SrOH). This is achieved with principal optical cycling in the rotationally closed $P\left(N"=1\right)$ branch of either the $\tilde{X}^{2}\Sigma^{+}\left(000\right)\leftrightarrow\tilde{A}^{2}\Pi_{1/2}\left(000\right)$ or the $\tilde{X}^{2}\Sigma^{+}\left(000\right)\leftrightarrow\tilde{B}^{2}\Sigma^{+}\left(000\right)$ vibronic transitions. Molecules lost into the excited vibrational states during the cooling process are repumped back through the $\tilde{B}\left(000\right)$ state for both the $\left(100\right)$ level of the Sr-O stretching mode and the $\left(02^{0}0\right)$ level of the bending mode. The transverse temperature of a SrOH molecular beam is reduced in one dimension by two orders of magnitude to $\sim700\ {\rm \mu K}$. This approach opens a path towards creating a variety of ultracold polyatomic molecules, including much larger ones, by means of direct laser cooling.