Toward Ultracold Polyatomic Molecules for Measuring the Electron's Electric Dipole Moment

Trapped, ultracold molecules are a potentially powerful platform for probing physics beyond the Standard Model. YbOH, which has recently been laser cooled in one dimension to <600 μK, is predicted to have high sensitivity to the electron electric dipole moment. Here, we report on work aiming to laser cool and trap large numbers of YbOH molecules in three dimensions. We have constructed a He-3-based cryogenic beam source, achieving forward velocities of Yb and YbOH below 30 m/s, and a superconducting Zeeman-Sisyphus decelerator, designed to slow molecules to trappable velocities using three photon scatters. To increase the number of molecules that could be trapped, we use a laser-assisted chemical reaction between Yb and H₂O to enhance molecular beam flux by more than an order of magnitude. We also present ultra-high-sensitivity measurements of vibrational branching ratios in YbOH, identifying vibrational states relevant for laser cooling using up to scattered 10⁵ photons. From these measurements, we determine a feasible laser cooling scheme to achieve trapped samples of YbOH.