Generalized Gibbs ensemble in a nonintegrable system with an extensive number of local symmetries.

Abstract

We numerically study the unitary time evolution of a nonintegrable model of hard-core bosons with an extensive number of local Z(2) symmetries. We find that the expectation values of local observables in the stationary state are described better by the generalized Gibbs ensemble (GGE) than by the canonical ensemble. We also find that the eigenstate thermalization hypothesis fails for the entire spectrum but holds true within each symmetry sector, which justifies the GGE. In contrast, if the model has only one global Z(2) symmetry or a size-independent number of local Z(2) symmetries, we find that the stationary state is described by the canonical ensemble. Thus, the GGE is necessary to describe the stationary state even in a nonintegrable system if it has an extensive number of local symmetries.