Many-body eigenstate thermalization from one-body quantum chaos: emergent arrow of time

TL;DR

This paper demonstrates that one-body quantum chaos alone can induce thermalization and an arrow of time in isolated many-body quantum systems, without the need for interactions or randomness.

Contribution

It reveals a new quantum thermalization mechanism driven by one-body chaos, challenging the belief that interactions or disorder are necessary for thermalization.

Findings

Quantum chaos leads to thermal distributions in eigenstates.

Thermalization occurs without interactions or randomness.

Emergence of the arrow of time in pure quantum states.

Abstract

A profound quest of statistical mechanics is the origin of irreversibility - the arrow of time. New stimulants have been provided, thanks to unprecedented degree of control reached in experiments with isolated quantum systems and rapid theoretical developments of manybody localization in disordered interacting systems. The proposal of (many-body) eigenstate thermalization (ET) for these systems reinforces the common belief that either interaction or extrinsic randomness is required for thermalization. Here, we unveil a quantum thermalization mechanism challenging this belief. We find that, provided one-body quantum chaos is present, as a pure many-body state evolves the arrow of time can emerge, even without interaction or randomness. In times much larger than the Ehrenfest time that signals the breakdown of quantum-classical correspondence, quantum chaotic motion leads to thermal [Fermi-Dirac (FD) or Bose-Einstein (BE)] distributions and thermodynamics in individual eigenstates. Our findings lay dynamical foundation of statistical mechanics and thermodynamics of isolated quantum systems.