Towards quantum degeneracy in a ⁸⁸Sr¹⁹F molecular gas

Despite the recent progress in direct cooling and trapping of molecules, the phase-space density of these systems is still low compared to atomic systems. This is due in large part to inefficient slowing, low magneto-optical trap (MOT) capture velocity, and sub-Doppler heating in the traditional red-detuned MOT. Such heating is a result of molecules’ type-II transition, where the excited state total angular momentum is less than or equal to the ground state angular momentum. Here, we present new methods to mitigate these issues.

We present an improved slowing scheme that uses a push beam and transverse cooling to increase the flux of capturable molecules. We also report on our experimental realization of a blue-detuned MOT that uses sub-Doppler cooling and trapping to significantly reduce the temperature and size of the molecular cloud relative to the red-detuned "capture" MOT; this should boost the efficiency of loading an optical dipole trap (ODT). We also discuss a novel two-color MOT that uses two excited states to increase the MOT capture velocity, and a scheme of implementing microwave shielding in order to suppress the two-body molecular inelastic collision rate. Finally, we detail a new vacuum chamber design with better vacuum lifetime, more optical access and integration with a Rb 2D MOT. These improvements should lead to the realization of a high phase-space density molecular gas and studies of collisions in it, paving the way towards molecular Bose-Einstein condensation.