Many-body physics is concerned with the emergent properties - those that characterize the collectivity but not the individual constituents - of macroscopic systems with large numbers of strongly interacting particles. Ensembles of many interacting particles can support qualitatively new phenomena, with the same system able to exist in different universal phases of matter with sharply distinct properties. Due to a variety of conceptual and experimentally motivated reasons, the modern theory of quantum many body systems is largely built around the study of low-temperature and near-equilibrium properties of time independent Hamiltonians. However, such systems represent a small subset of the possible quantum mechanical descriptions of a physical system - which allow for more general unitary evolutions interrupted by non-unitary measurements. I will describe some highlights of an active research program to advance many-body theory beyond the regime of near-equilibrium time-independent Hamiltonians, with a view towards uncovering novel complex emergent phenomena in new non-equilibrium regimes. A notable recent example is the discovery of the Floquet time-crystal, a phase of matter that is provably disallowed in thermal equilibrium. These theoretical efforts are synergistic with recent advances in building controllable quantum devices that naturally implement more general time evolutions generated by circuits of unitary gates, starting from initial states that are not low energy in any useful sense.
About the Speaker
Vedika Khemani started as an Assistant Professor of Physics at Stanford in 2019. After graduating from Princeton in 2016, she spent her postdoctoral years as a Junior Fellow at the Harvard Society of Fellows. In 2020, she was awarded a Sloan Research Fellowship, a DOE Early Career Award, the McMillan Award for Condensed Matter Physics, and the American Physical Society’s George E Valley Jr. Prize, "For seminal theoretical work on novel phases of many-body localized and Floquet systems, including demonstrating the absolute stability of a time crystal in such systems."