Exact Thermal Stabilizer Eigenstates at Infinite Temperature

TL;DR

This paper constructs exact infinite-temperature eigenstates of nonintegrable quantum Hamiltonians using stabilizer states, demonstrating their ability to reproduce thermal expectations for local observables and exploring the limitations imposed by stabilizer structure.

Contribution

It introduces a method to construct exact thermal eigenstates using stabilizer states for nonintegrable Hamiltonians and proves a no-go theorem regarding their thermalization capabilities.

Findings

Stabilizer eigenstates can reproduce thermal expectations for all local observables.

A no-go theorem shows stabilizer eigenstates cannot satisfy all four-body thermal correlations.

Explicit construction of a Hamiltonian with stabilizer eigenstates thermal for two- and three-body observables.

Abstract

Understanding how microscopic few-body interactions give rise to thermal behavior in isolated quantum many-body systems remains a central challenge in nonequilibrium statistical mechanics. While individual energy eigenstates are expected to reproduce thermal equilibrium values, analytic access to highly entangled thermal eigenstates of nonintegrable Hamiltonians remains scarce. In this Letter, we construct exact infinite-temperature eigenstates of generically nonintegrable two-body Hamiltonians using stabilizer states. These states can fully reproduce thermal expectation values for all spatially local observables, extending previously known Bell-pair-based constructions to a broader class. At the same time, we prove a sharp no-go theorem: stabilizer eigenstates of two-body Hamiltonians cannot satisfy microscopic thermal equilibrium for all four-body observables. This bound is tight, as we explicitly construct a translationally invariant Hamiltonian whose stabilizer eigenstate is thermal for all two-body and three-body observables as well as all spatially local observables. Our results suggest that reproducing higher-order thermal correlations requires nonstabilizer degrees of freedom, providing analytic insight into the interplay between interaction locality, microscopic thermal equilibrium, and quantum computational complexity.