Polyatomic molecules are projected to be powerful tools in the search for physics beyond the Standard Model (BSM), including new CP-violating (CPV) interactions and ultralight dark-matter (UDM) particles [I. Kozyryev et al., Phys. Rev. A 103, 043313 (2021); Phys. Rev. Lett. 119, 13302 (2017)]. Certain degrees of freedom present in polyatomic molecules enhance the sensitivity of these searches, as well as reject systematic errors, but necessitate extensive high-precision spectroscopy to identify pathways for optical cycling and quantum state readout. Here we show how a magneto-optical trap can be used to locate weak optical transitions and identify rovibronic states for optical cycling and quantum control. We demonstrate this spectroscopic approach with strontium monohydroxide (SrOH), which is a candidate for both CPV and UDM searches [Z. D. Lasner et al., Phys. Rev. Lett. 134, 083401 (2025); I. Kozyryev et al., Phys. Rev. A 103, 043313 (2021); Phys. Rev. Lett. 119, 13302 (2017)]. We identify two repumping transitions in SrOH and implement them in a deeper optical cycle to achieve 32400(4700) trapped molecules, which is a 4.5-fold increase over the previous, shallower cycle. In addition, we determine the energy spacing between the ${\tilde{X}}^2{\mathrm{\Sigma }}^{+}\left(200\right)$ and ${\tilde{X}}^2{\mathrm{\Sigma }}^{+}\left({03}^{1}0\right)$ vibrational manifolds of SrOH, confirming the existence of numerous low-frequency rovibrational transitions that are sensitive to temporal variations of the proton-to-electron mass ratio, a predicted effect of the existence of UDM.

Close

PrevNext

View figure in article

• Molecular spectra
• Molecule trapping & guiding
• Molecules
• Vibronic spectroscopy