Quantum degeneracy and interactions in the rubidium-87-potassium-40 Bose-Fermi mixture

An apparatus for producing dilute-gas quantum degenerate Bose-Fermi mixtures is presented. The experiment uses forced evaporative cooling to obtain a nearly pure 87Rb Bose-Einstein condensate immersed in a gas of sympathetically cooled 40K atoms at 0.2 times the Fermi temperature. The design, construction, and operation of the apparatus are described in detail. The onset of quantum degeneracy is characterized and contrasted between species, revealing the effects of quantum statistics on the bulk properties of the gases.; The apparatus is then used to study the interactions between species in ultracold non-degenerate mixtures. Measurements of rethermalization rates are used to determine the elastic scattering cross-section between species. From these measurements the magnitude of the inter-species s-wave scattering length is determined. The scattering length is central to characterizing a variety of static and dynamic properties of the mixture. The apparatus is additionally used to study for the first time Feshbach resonances in the collisions between 87Rb and 40K atoms. These resonances present a means for experimentally tuning the scattering length between species to any desired value. Prospects for future experiments exploiting this real-time control over the interactions are discussed.