Dynamics of quantum many-body systems

University Of Maryland, College Park, College Park MD

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports fundamental theoretical condensed matter research and education aiming to extend our understanding of nonequilibrium quantum matter. A typical material or electronic device contains an immense number of electrons, which constitute a quantum many-body system - the subject of condensed matter research. The corresponding configuration space, the set of possible states the system can find itself in, is unimaginably large. In thermodynamic equilibrium, the situation is somewhat simplified in that the system occupies states that are close to the lowest-energy state in a rigorously prescribed manner, exploring only a tiny corner of the entire configuration space. This leads to a material with well-defined properties that are dictated by nature and are "non-negotiable." In contrast, a nonequilibrium system can explore the totality of the huge configuration space and may potentially find itself in a state with drastically modified electronic properties compared to those at equilibrium. Therefore, the ability to control dynamical properties of driven electronic states could open opportunities to design nonequilibrium electronic materials with desired properties, instead of relying on serendipity in equilibrium material physics. This project is focused on exploring fundamental aspects of the underlying physics that would make such nonequilibrium quantum control of electronic materials possible. Of particular interest in this project are many-body quantum systems under the influence of perturbations that are periodic in time, which in practice is often achieved by irradiating electronic materials by light. The project achieves broader impacts by bringing together ideas from different fields of physics and mathematics, integrating them into teaching, and communicating them to a wide audience, building on the PI's prior efforts. Mentoring of students will continue and will include a continuing collaboration with the Science Magnet Program at Montgomery Blair High School in Silver Spring, MD, and the historically black Howard University in Washington, DC. The outreach component will also include further development and refinement of PI's massive open online course "Exploring Quantum Physics." TECHNICAL SUMMARY This award supports fundamental theoretical condensed matter research and education aiming to extend our understanding of nonequilibrium quantum matter. The emphasis is on relating exciting theoretical results and ideas to experiment, and communicating them to a broad audience. The research effort is focused on studies of dynamics of quantum many-body systems. Below is a list of three key research foci: 1. A periodically-driven rotor is a prototypical model that exhibits a transition to chaos in the classical regime and dynamical localization in the quantum regime. The Principal Investigator will explore interacting many-body generalizations of such nonlinear, periodically driven systems, which are expected to exhibit transitions from many-body quantum chaos to dynamical localization. 2. Recent experiments have observed interesting light-induced states in topological materials, such as Floquet reconstruction of electronic bands by light and a photovoltage and gigantic surface life-time in topological insulators. Motivated by this experimental progress, this project aims to develop a theory of Floquet systems coupled to a heat bath. An ambitious goal here is to identify general principles of Floquet thermodynamics. 3. Solitons are fascinating nonlinear phenomena that occur in a diverse array of classical and quantum systems. Relying on a series of exact results, obtained recently by the PI, it is proposed to consider dissipative dynamics of quantum solitons in superfluids. The study of nonequilibrium many-body systems would provide new insights into several classes of physically interesting and technologically important materials and has the potential to deliver results of fundamental and practical importance. For example, an understanding of the long-lived photoexcited states in topological insulators may provide a roadmap for creating novel devices, such as an optical p-n junction and a solar cell, based on light-induced topological surface states. The project achieves broader impacts by bringing together ideas from different fields of physics and mathematics, integrating them into teaching, and communicating them to a wide audience, building on the PI's prior efforts. Mentoring of students will continue and will include a continuing collaboration with the Science Magnet Program at Montgomery Blair High School in Silver Spring, MD, and the historically black Howard University in Washington, DC. The outreach component will also include further development and refinement of PI's massive open online course "Exploring Quantum Physics."