Modern concepts of quantum equilibration do not rule out strange relaxation dynamics

Abstract

Numerous pivotal concepts have been introduced to clarify the puzzle of relaxation and/or equilibration in closed quantum systems. All of these concepts rely in some way on specific conditions on Hamiltonians H, observables A, and initial states rho or combinations thereof. We numerically demonstrate and analytically argue that there is a multitude of pairs H, A that meet said conditions for equilibration and generate some typical expectation-value dynamics, which means (A(t)) alpha f (t) approximately holds for the vast majority of all initial states. Remarkably we find that, while restrictions on the f (t) exist, they do not at all exclude f (t) that are rather adverse or strange regarding thermal relaxation.