Spectroscopy of Vibrational Branching in Low-Symmetry Molecules

Symmetric and asymmetric top molecules are of generic interest to precision measurement and quantum information experiments due to long-lived (>10 s) parity doublets in the electronic ground state [1, 2]. To access these states, such species need to be cooled to ~mK temperatures. Laser deceleration and cooling are conceptually simple methods of doing so, but require ~10^4 scattered photons to remove sufficient momentum. To scatter this many photons in a molecule, it is necessary to identify statistical vibrational leakage out of the main vibronic transition and close these channels to maintain an optical cycle. This leakage is generically difficult to calculate numerically at high precision, and, as such, must be measured experimentally [3]. We present here measurements of vibrational branching ratios of several strontium- and calcium-containing M-R (where R is a halogenic molecular ligand) low-symmetry molecules to assess this aspect of the challenge in extending full laser cooling to such species. In the process, we seek to identify trends along both the metal mass and ligand complexity axes of the molecular parameter space. Though some additional spectroscopy would be necessary to fully cool these species, our measurements provide enough information to attempt 1D and 2D cooling of several target species. Future directions of study to enable full laser cooling of low-symmetry species are also discussed.

[1] Kozyryev, Hutzler, Phys. Rev. Lett. 119 2017

[2] Albert et al, Phys. Rev. X 10 2020

[3] Augenbraun et al, Phys. Rev. X 10 2020