Asymmetric Top Molecules for Quantum Science: From Bent Triatomics to Functionalized Aromatic Species

The diversity of electronic structures, geometries, and atomic constituents present in polyatomic molecules potentially makes them powerful building blocks for next-generation experiments in quantum science and precision measurement. Using complex molecules for these applications requires us to confront one of their most defining characteristics: molecular asymmetry. Until recently, the lack of strict selection rules was thought to make infeasible the laser-based control of asymmetric top molecules (ATMs; molecules with three distinct moments of inertia). We have shown that this is likely not the case and have put forward an experimental toolbox for optical cycling and laser cooling of ATMs. In addition, we have proposed theoretical design principles that allow pushing beyond the M-O-R motif that is characteristic of the polyatomic molecules that have so far been laser cooled—opening up a wider world of unusual geometries and ro-vibrational modes for scientific use. Experimental studies of the molecules CaSH, CaNH$_2$, and CaOC₆H₅ validate key findings of our theoretical results and demonstrate initial progress toward optical cycling and laser cooling of ATMs.