Signatures of rare states and thermalization in a theory with confinement

摘要: There is a dichotomy in the nonequilibrium dynamics of quantum many-body systems. In presence integrability, expectation values local operators equilibrate to described by generalized Gibbs ensemble, which retains extensive memory about initial state system. On other hand, generic systems such relax stationary thermal fixed solely energy state. At heart understanding, this eigenstate thermalization hypothesis (ETH): individual eigenstates nonintegrable are thermal, sense that agree with prediction at temperature set eigenstate. where ETH violated, can be avoided. Thus, establishing range validity crucial understanding whether given system thermalizes. Here, we study simple model confinement, Ising chain longitudinal field, violated. Despite an absence there exist rare (nonthermal) states persist far into spectrum. These arise as direct consequence confinement: pairs particles confined, forming new “meson” excitations whose size. We show nonthermal both continuum and low-energy spectrum corresponding lattice model. highlight within has important consequences, certain quenches leading observables evolving anomalously.