Tyler Cumby

Tests of Universal Three-Body Physics in an Ultracold Bose-Fermi Mixture

Recent measurements of Efimov resonances for a number of ultracold atom species have revealed an unexpected universality, in which three-body scattering properties are determined by the van der Waals length of the two-body interaction potential. To investigate whether this universality extends to heteronuclear mixtures, we measure loss rate coefficients in an ultracold trapped gas of 40K and 87Rb atoms. We find an Efimov-like resonance in the rate of inelastic collisions between 40K87Rb Feshbach molecules and 87Rb atoms. However, we do not observe any Efimov-related resonances in the rates of inelastic collisions between three atoms. These observations are compared to previous measurements by the LENS group of Efimov resonances in a 41K and 87Rb mixture as well as to recent predictions.

Coherent atom-molecule oscillations in a Bose-Fermi mixture

We create atom-molecule superpositions in a Bose-Fermi mixture of

Feshbach-molecule formation in a Bose-Fermi mixture

^{87}\text{R}\text{b}

Efimov physics in an ultracold Bose-Fermi gas of ~

and

{ }^{40}K

^{40}\text{K}

and

atoms. The superpositions are generated by ramping an applied magnetic field near an interspecies Fano-Feshbach resonance to coherently couple atom and molecule states. Rabi- and Ramsey-type experiments show oscillations in the molecule population that persist as long as

{ }^{87}Rb

150\text{ }\ensuremath{\mu}\text{s}

atoms

and have up to 50% contrast. The frequencies of these oscillations are magnetic-field dependent and consistent with the predicted molecule binding energy. This quantum superposition involves a molecule and a pair of free particles with different statistics (i.e., bosons and fermions) and furthers exploration of atom-molecule coherence in systems without a Bose-Einstein condensate.