Quenched Magneto-association of Ultracold Feshbach Molecules

Abstract

We study enhanced magneto-association of atoms into weakly-bound molecules near a Feshbach resonance using a quench preparatory stage. In anticipation of experiments with NASA's Cold Atom Laboratory aboard the International Space Station, we assume as a baseline a dual-species ($^{87}$Rb and $^{41}$K) gas in a parameter regime enabled by a microgravity environment. This includes subnanokelvin temperatures and dual-species gases at densities as low as 10$^8$/cm$^3$. Our studies indicate that, in such a regime, traditional magneto-association schemes are inefficient due to the weak coupling between atomic and molecular states at low-densities, thus requiring extremely long magnetic field sweeps. To address this issue we propose a modified scheme where atoms are quenched to unitarity before proceeding with magneto-association. This substantially improves molecular formation, allowing for up to $80\%$ efficiency, and within time-scales much shorter than those associated to atomic and molecular losses. We show that this scheme also applies at higher densities, therefore proving to be of interest to ground-based experiments as well.