Characterizing the Feshbach association of ²³Na⁴⁰K molecules

The conversion of a mixture of Bose-Fermi atomic gases into fermionic Feshbach molecules, by sweeping the magnetic field across a Feshbach resonance, is limited by inelastic collisional loss. To characterize the loss during the association, we systematically measure the dimer-dimer, atom-dimer, and three-body loss in the ²³Na-⁴⁰K system and compare the loss with the zero-range scattering theory. We identify that the collisional loss between the sodium atoms and the Feshbach molecules is the bottleneck of the association. We observe surprisingly long-lived Feshbach molecules and a universal a^3 dependence of the fermionic dimer-dimer loss coefficient. Moreover, we observe a suppression of the three-body loss at unitary regime by Fermi degeneracy. These studies make it possible to prepare degenerate NaK Feshbach molecules.