Expansion Dynamics and Prethermalization in Ultracold Quantum Gases

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Progress in science in general, and physics in particular, comes in many flavors. Often experimental observations of an unexpected phenomenon, such as high-temperature superconductivity, trigger the development of new theories. It also happens sometimes that "thought experiments" result in new theories, such as general relativity, that are later tested in actual experiments. In the field of ultracold quantum gases, gases at temperatures that are in the nano-Kelvin regime trapped by means of magnetic fields in ultrahigh vacuum (the ultracold counterpart of plasmas), experimental and theoretical developments often go hand in hand. Experiments with ultracold quantum gases have motivated many recent developments in statistical physics. They have also tested theoretical predictions with an exceptional accuracy. This project involves a close collaboration between the theoretical group of the PI and experimental groups in the US and Europe. The goal is to develop and test increasingly sophisticated theoretical descriptions of nonequilibrium quantum systems while contributing to the development and testing of progressively more accurate and controllable experimental platforms. Under this award, graduate students will be trained in quantum physics and computational physics (e.g., they will write and run codes for supercomputers). The PI will deliver lectures about the experimental and theoretical developments at the local high school to motivate students to pursue careers in STEM. The PI will study the quantum dynamics of ultracold one-dimensional (1D) gases locally far from equilibrium, as well as their expansion dynamics in 1D. After long expansion times in 1D, the latter dynamics enables the experimental measurement of rapidity distributions, long-thought "theoretical constructs" that were recently measured in a collaboration between the PI and groups at Penn State. A central goal of the new studies will be to test the recently developed theory of generalized hydrodynamics (GHD), and to identify corrections beyond GHD that need to be accounted for theoretically. A second topic to be explored is the dynamics of systems with weakly broken integrability (and, more generally, weakly broken conservation laws) to experimentally test a recently developed theory of prethermalization, and to search for its limits of applicability. A central goal here will be to develop theoretical/experimental tools to predict/measure thermalization rates in a broad range of systems. In addition, the PI's group will develop generalizations of a recently introduced theoretical approach to study equilibrium and far-from-equilibrium dynamics of impenetrable SU(N) fermions, and will study the off-diagonal matrix elements of observables in the eigenstates of integrable interacting Hamiltonians to understand what they can teach us about quantum dynamics and transport close to integrability.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.