Of great interest to the University of Chicago MRSEC are studies of systems far from equilibrium. In this context, IRG 4 is addressing the dynamics associated with a rapid quench of a superconductor or superfluid. In such a quench one makes an abrupt change in the strength of the interaction and observes the subsequent effects associated with the behavior of the time dependent density-density correlation functions. In solid state materials there is very little access to this dynamics because one has no knob to effect changes in the interaction strength.
Left Experiment: Oscillation of the density structure factor in the time domain. (a) quenches from high to low coupling constant. (b) quenches from low to high coupling constant.
Right Theory: Damped oscillations (arising from the equilibration bath) are seen when comparing the red and blue curves.
Chin and collaborators have studied quench dynamics in a two dimensional Bose gas using a Feshbach resonance to change the interaction strength. They have identified the resulting short time oscillatory behavior with acoustic Sakharov oscillations. Sakharov oscillations refer to interfering acoustic waves that are synchronously generated throughout a fluid. Experimentally, these appear to be a generic feature, observed in the weak and strong interaction regime. Levin’s groupis addressing Chin’s data by building an extension of time dependent Bogoliubov theory. Unlike previous theoretical studies their work includes the presence of a thermal bath. This bath is essential for ultimate equilibration. Of great interest in future will be a comparison between the quench dynamics of bosonic and fermionicsuperfluids. This body of work suggests new perspectives to formulate nonequilibrium dynamics of quantum many-body systems and to explore its analogues in cosmology and astrophysics.