Work Extraction from a Single Energy Eigenstate

TL;DR

This paper investigates whether work can be extracted from a single energy eigenstate, finding that in non-integrable systems, quantum chaos enforces a stronger second law, preventing work extraction.

Contribution

It demonstrates that in non-integrable systems, work cannot be extracted from individual energy eigenstates, linking ETH and quantum chaos to thermodynamic irreversibility at the eigenstate level.

Findings

Work extraction from a single eigenstate is impossible in non-integrable systems.

Quantum chaos enforces a stronger second law at the eigenstate level.

Numerical evidence shows zero work-extractable eigenstates in finite non-integrable systems.

Abstract

Work extraction from the Gibbs ensemble by a cyclic operation is impossible, as represented by the second law of thermodynamics. On the other hand, the eigenstate thermalization hypothesis (ETH) states that just a single energy eigenstate can describe a thermal equilibrium state. Here we attempt to unify these two perspectives and investigate the second law at the level of individual energy eigenstates, by examining the possibility of extracting work from a single energy eigenstate. Specifically, we performed numerical exact diagonalization of a quench protocol of local Hamiltonians and evaluated the number of work-extractable energy eigenstates. We found that it becomes exactly zero in a finite system size, implying that a positive amount of work cannot be extracted from any energy eigenstate, if one or both of the pre- and the post-quench Hamiltonians are non-integrable. We argue that the mechanism behind this numerical observation is based on the ETH for a non-local observable. Our result implies that quantum chaos, characterized by non-integrability, leads to a stronger version of the second law than the conventional formulation based on the statistical ensembles.