Technical Improvements Towards Realizing a Quantum Degenerate Gas of SrF Molecules

Tremendous progress has been made in direct laser cooling and trapping of molecules. We recently demonstrated trapping of SrF molecules at sufficient densities to observe loss from inelastic molecule-molecule collisions. Our next goal is to implement microwave shielding, which promises to suppress these losses while enhancing the elastic collision rate; this is ideal for evaporative cooling to quantum degeneracy. Microwave shielding has been achieved in bialkali assembled molecules (where quantum degeneracy was achieved) and in optical tweezers of single CaF molecules, but has yet to be successfully realized in a bulk sample of laser-cooled SrF molecules. The substantial spin-rotation splitting in SrF (75 MHz) requires comparably high microwave Rabi frequencies for effective shielding. We intend to accomplish this using a high-gain horn antenna and ellipsoidal focusing mirror to deliver a focused, free-space microwave beam at the molecules. Using this system, we aim to achieve Rabi frequencies up to 50 MHz, shielding state lifetime in excess of 1 second, and polarization purity of greater than 90% circular. In addition, we have constructed a second-generation apparatus for our experiment, which features a number of upgrades designed to help increase the particle number in and phase-space density of our bulk gas. This includes reduced source slowing length and a fully integrated rubidium MOT for sympathetic cooling.