CAREER: Non-equilibrium quantum dynamics, topology, and criticality

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NONTECHNICAL SUMMARYThis CAREER award supports theoretical research and education towards understanding and controlling the dynamics of complex quantum systems. The peculiar properties of quantum mechanics enable fundamentally new computing, cryptographic, and communication methods that far outpace their classical counterparts. Harnessing these properties for technology requires the ability to control and manipulate complex physical systems while preserving their delicate quantum structure. To date, quantum technologies have only been successfully implemented in very small systems for which every detail can be completely characterized and controlled, presenting a barrier to large scale implementation. In contrast, macroscopic quantum materials exhibit remarkable universal phenomena, e.g. superconductivity and magnetism, that are insensitive to the underlying minutiae. However, these complex quantum systems often have too many moving parts to precisely control, typically leading to rapid scrambling of encoded information before it can be utilized.This project aims to bridge the gap between these two regimes by identifying robust, error-resistant ways to control quantum motion in macroscopic systems, without separately controlling each individual piece. This will be done by exploring new realms of matter in isolated quantum systems that are cut off from the outside world, but are driven far from conventional equilibrium settings using, for example, irradiation by modulated light. The research will build new theoretical and computational tools for simulating the dynamics of complex quantum systems, and develop universal organizing principles to understand their properties. Graduate and undergraduate students will play an integral role in the research efforts, while building towards their degrees. In conjunction, the PI will create new and enhance existing K-12 outreach programs for students, building opportunities for women, persons with disabilities, and for underrepresented minority groups to learn about and participate in scientific research. The PI will also develop a new interdisciplinary university curriculum to build interdisciplinary connections among increasingly symbiotic but traditionally separated subfields of theoretical physics.TECHNICAL SUMMARYThis CAREER award supports theoretical research and education to identify, understand, and control universal regimes of coherent nonequilibrium dynamics in complex quantum many-body systems. Universality is typically elusive in complicated many-body systems, as their chaotic internal dynamics rapidly lead towards thermal equilibrium producing incoherent classical dynamics. This project seeks to find intrinsically quantum coherent dynamical steady states that defy the "laws" of thermal equilibrium, and consists of three thrusts:1) Isolating a system from its environment, and adding strong disorder can indefinitely prevent thermalization and lead to the phenomena of many-body localization. The PI will investigate how equilibrium thermodynamics breaks down sharply at the onset of localization by developing new numerical renormalization group techniques and analytic methods based on tensor-network methods to describe this new class of critical phenomena.2) Driving a quantum system in a time-dependent fashion can achieve nonequilibrium steady states. The PI will explore how new dynamical topological phases with no equilibrium analog can be engineered by driving.3) The PI will investigate how non-thermal states and quantum dynamics can be used to build entangled light sources, to access new nonequilibrium phases in dissipative systems, and to devise new ways to dynamically probe the properties of equilibrium quantum materials.These directions are inspired by rapid experimental progress in atomic, molecular, and optical systems that can be well isolated from their environment and can be dynamically manipulated with great precision and flexibility. The proposed research can enable novel dynamical macroscopic quantum phenomena in these systems without the need for stringent cooling, offering strong advantages for their experimental exploration. Applications of these ideas to solid-state systems and new computational methods will also be developed.Graduate and undergraduate students will play an integral role in the research efforts, while building towards their degrees. In conjunction, the PI will create new and enhance existing K-12 outreach programs for students, building opportunities for women, persons with disabilities, and for underrepresented minority groups to learn about and participate in scientific research. The PI will also develop a new interdisciplinary university curriculum to build interdisciplinary connections among increasingly symbiotic but traditionally separated subfields of theoretical physics.