## Yale Graduate School of Arts and Sciences Dissertations

Spring 2021

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

#### Department

Physics

Polar molecules can interact via the anisotropic and long-range electric dipole-dipole interaction owing to their large permanent electric dipole moments. Being able to study them in the ultracold temperature regime and at high density would allow us to study strongly correlated physics, and expand the toolbox for quantum computation. In order to reduce the temperature of SrF beyond the sub-Doppler temperature ($\sim10$ $\mu$K) achieved with laser cooling by polarization gradients, we hope to implement sympathetic cooling of SrF and Rb. Pursuing this direction requires advancements in experimental capabilities. This thesis describes the experimental efforts towards co-trapping SrF and Rb, which is the starting point of studies of atom-molecule collisions in the ultracold temperature regime. The thesis reports on some technical aspects of conservative trapping: a high-power circuit was developed to facilitate current switching in the context of magnetic quadrupole traps, and depths of optical dipole traps were estimated in anticipation of complexities due to a strongly state-dependent trapping potential. The thesis also details the construction and performance of an apparatus for laser cooling and trapping Rb. The apparatus consists of a 2D MOT that functions as a high-flux beam source of Rb, and an RF MOT. The 2D MOT produces a flux on the order of 10$^{9}$ atoms/s. With 500-ms loading, the RF MOT is able to collect $\sim$10$^9$ atoms at temperatures $\sim$1 mK. Compared to the molecule number typical in an SrF MOT, the atom number in the Rb RF MOT is 10$^4$ higher, suggesting good prospects of observing atom-molecule collisions in a subsequent conservative trap. In addition, we established a comparison between the dc and RF MOT of Rb in the same apparatus. We found that in an RF MOT, the number is significantly lower and the temperature significantly higher, while the loading time constant and lifetime are similar to those of a dc MOT.