Feshbach molecule formation in a Bose-Fermi mixture

TL;DR

This study demonstrates efficient formation of Feshbach molecules in a Bose-Fermi mixture, revealing how conversion efficiency depends on density overlap and phase-space density, with deviations at quantum degeneracy.

Contribution

It provides experimental insights into molecule formation efficiency and phase-space effects in Bose-Fermi mixtures, supported by a parameter-free model and phenomenological analysis.

Findings

Achieved up to 7×10^4 molecules with 45% efficiency

Conversion efficiency depends linearly on density overlap in the perturbative regime

Fewer molecules are formed than predicted in quantum degenerate regimes

Abstract

We investigate magnetoassociation of ultracold fermionic Feshbach molecules in a mixture of $^{40}$K and $^{87}$Rb atoms, where we can create as many as $7\times 10^4$ $^{40}$K$^{87}$Rb molecules with a conversion efficiency as high as 45%. In the perturbative regime, we find that the conversion efficiency depends linearly on the density overlap of the two gases, with a slope that matches a parameter-free model that uses only the atom masses and the known Feshbach resonance parameters. In the saturated regime, we find that the maximum number of Feshbach molecules depends on the atoms' phase-space density. At higher temperatures, our measurements agree with a phenomenological model that successfully describes the formation of bosonic molecules from either Bose or Fermi gases. However, for quantum degenerate atom gas mixtures, we measure significantly fewer molecules than this model predicts.