Thermalization without eigenstate thermalization hypothesis after a quantum quench

TL;DR

This paper demonstrates that certain nonintegrable quantum systems can thermalize after a quench without satisfying the eigenstate thermalization hypothesis, especially in the thermodynamic limit, and explores conditions affecting thermalization.

Contribution

It reveals that nonintegrable systems can thermalize without eigenstate thermalization hypothesis and characterizes the role of system size and temperature in this process.

Findings

System thermalizes after a quantum quench in the thermodynamic limit.

Finite systems at low temperature may not thermalize.

Prethermalization occurs with nonthermal energy eigenstates.

Abstract

Nonequilibrium dynamics of a nonintegrable system without the eigenstate thermalization hypothesis is studied. It is shown that, in the thermodynamic limit, this model thermalizes after an arbitrary quantum quench at finite temperature, although it does not satisfy the eigenstate thermalization hypothesis. In contrast, when the system size is finite and the temperature is low enough, the system may not thermalize. In this case, the steady state is well described by the generalized Gibbs ensemble constructed by using highly nonlocal conserved quantities. We also show that this model exhibits prethermalization, in which the prethermalized state is characterized by nonthermal energy eigenstates.