|Title||Dynamics of Quenched Ultracold Quantum Gases|
|Year of Publication||2016|
|Number of Pages||132|
|University||University of Colorado|
Recent advances in the tunability of ultracold atomic gases have created opportunities for studying interesting quantum many-body systems. Fano-Feshbach resonances, in particular, allow experimenters to freely adjust the scattering of atoms by controlling an external magnetic field. By rapidly changing this field near a resonance, it is possible to drive systems out of equilibrium towards novel quantum states where correlations between atoms change dynamically. In this thesis, we take a wave-function-based approach to theoretically examine the response of several interesting systems to suddenly-switched, or “quenched,” interactions.
We first calculate the time evolution of a Bose-Einstein condensate that is quenched to the unitarity regime, where the scattering length α diverges. Working within the time-dependent variational formalism, we find that the condensate does not deplete as quickly as the usual Bogoliubov theory would suggest. We also make a quantitative prediction for the dynamics of short-range pair correlations, encoded in Tan’s contact. We then consider the dynamics of these correlations for quenches to small α, and we find that bound states can cause high contrast oscillations of the contact. These dynamics can be modelled quantitatively at short times by using a properly chosen two-body model. Finally, we characterize the nonlocal correlation waves that are generated by an interaction quench in arbitrary dimensionality. Our analysis demonstrates that the large momentum limit of the post-quench momentum distribution can sometimes include contributions from both the short range and the long range, depending on the quench protocol.