Efimov Resonances in an Ultracold Mixture with Extreme Mass Imbalance

Abstract

This thesis reports on the investigation of few-body physics in an ultracold mass-imbalanced mixture at large scattering lengths. For this purpose, a new apparatus for the creation of quantum degenerate 6Li and 133Cs gases has been built. We measure 19 interspecies Feshbach resonances in the two energetically lowest hyperfine channels of each species of an ultracold mixture with temperatures on the uK scale. We apply and compare a coupled-channels calculation, the asymptotic bound-state model, and the multichannel quantum defect theory for the calculation of the Feshbach resonance positions. All models provide a consistent and accurate description of the two-body scattering resonances in the mixture. Three-body loss rate measurements on the negative scattering length side of a broad Feshbach resonance in the energetically lowest hyperfine channel at 450 nK reveal two consecutive Efimov resonances. The scattering lengths assigned to the two Efimov resonances yield a scaling ratio that is consistent with a universal prediction in the zero temperature and resonant limit. The presented measurements provide the first test for universal few-body theories of mixed-species systems with large mass-imbalance.