Thermalization of isolated quantum many-body system and entanglement

Abstract

Thermalization of an isolated quantum system has been a non-trivial problem since the early days of quantum mechanics. In generic isolated systems, non-equilibrium dynamics is expected to result in thermalization, indicating the emergence of statistical mechanics from quantum dynamics. However, what feature of many-body quantum system facilitates quantum thermalization is still not well understood. Here we revisit this problem and show that introduction of entanglement in the system gives rise to thermalization, and it takes place at the level of individual eigenstate. We also show that the expectation value in the energy eigenstate of each subsystem is close to the canonical average.