Breakdown of thermalization in quantum systems: analytical and numerical approaches

Recent experimental advances have enabled realization of synthetic quantum systems with many particles. Examples include ultracold atoms in laser traps and superconducting qubits. These systems have provided ideal platforms to investigate non-equilibrium quantum dynamics, which previously has been out of reach.

In recent years, theoretical investigations have focused on describing universality classes of quantum dynamics. Remarkably, classes of systems which do not reach thermal equilibrium, were discovered. Such systems go beyond conventional statistical mechanics, and new analytical and numerical tools are necessary. The interest in non-thermalizing systems stems from their fundamental and technological importance. In particular, as shown by the Geneva team, absence of thermalization allows one to protect quantum coherence and realize new non-equilibrium states of matter.

In parallel, thermodynamics of black holes, quantum chaos, and universality of quantum dynamics have been actively studied in the context of quantum gravity. It has become evident that the two communities (condensed matter and quantum gravity) are largely interested in the same set of questions, but approach them using very different sets of tools. There is clearly strong potential for collaboration between the two communities, which will reveal new connections between synthetic quantum systems studied in the lab and quantum effects of gravity exemplified by the black holes.

The goal of this project is to establish a collaboration on quantum dynamics between two teams, at UniGe and SkolTech, led by D. Abanin and A. Dymarsky. The two teams have made key contributions to the recent developments in the field, in particular, developing theories of thermalization and its breaking. The teams have condensed matter and quantum gravity backgrounds respectively, which provides foundation for synergetic activities. The expertise of the Geneva team includes condensed matter techniques and numerical methods for non-equiliubirum lattice systems, while the Moscow team focuses on holographic correspondence and field-theoretic approaches. In this project, these very different tools will be combined to make progress in describing universality classes of quantum dynamics.

We plan to investigate two classes of phenomena: quantum many-body scars and prethermalization, and to link them to quantum chaos.

Quantum many-body scars is a novel mechanism to avoid thermalization, introduced recently by the Geneva team. In particular, several constrained lattice models exhibiting quantum scars have been constructed. As a part of this project, we aim to develop field-theoretic description for such systems and reveal classes of theories that exhibit non-thermalization dynamics via the “scar” mechanism. Furthermore, connections between the models exhibiting quantum scars and integrable models will be clarified, and new exactly solvable models will be constructed.

Prethermalization – the ability of a system to thermalize parametrically slowly – is the second direction in which both teams have significant complementary expertise. The Geneva team have rigorously established general conditions for prethermalization in Floquet systems. The Moscow team has discovered promising analytic connections between prethermalization, operator growth, and quantum chaos. This will form the basis for a long-term collaboration.

This project will establish a collaboration on quantum dynamics, involving PIs, postdocs, and students, preparing the teams for joint funding opportunities.

Participants:

University of Geneva:

  • Prof. Dimitry Abanin
  • Dr. Alessio Lerose
  • Mr. Michael Sonner

Skoltech: