Vibrational Branching Ratios for Laser-Cooling of Nonlinear Strontium-Containing Molecules

TL;DR

This paper measures vibrational branching ratios in specific strontium-containing molecules to evaluate their suitability for laser cooling, combining experimental data with ab initio calculations and symmetry analysis.

Contribution

It provides the first precise measurements of vibrational branching ratios for these molecules and supports laser cooling prospects through combined experimental and theoretical analysis.

Findings

Favorable vibrational branching ratios for SrNH2

Support for laser cooling of SrOCH3 and SrSH

Potential for beyond Standard Model physics searches

Abstract

The vibrational branching ratios from the lowest excited electronic state for $\textrm{SrOCH}_3$, $\textrm{SrNH}_2$, and $\textrm{SrSH}$ are measured at the $< 0.1\%$ level. Spectra are obtained by driving the $\tilde{X} - \tilde{A}$ transitions and dispersing the fluorescence on a grating spectrometer. We also perform $\textit{ab initio}$ calculations for the energies of vibrational levels relevant for laser cooling, as well as branching ratios to support the interpretations of all molecular spectra. Symmetry group analysis is applied in conjunction with our data to study rotational closure in these molecules. These analyses indicate favorable prospects for laser cooling $\textrm{SrNH}_2$ and other similar alkaline-earth(-like) amides for future beyond the Standard Model physics searches using polyatomic molecules with long-lived parity doublets.