title: Stationary ensemble approximations of dynamic quantum states: Optimizing the generalized Gibbs ensemble.
abstract: In this work we investigate the nonequilibrium dynamics of closed quantum systems. In particular we focus on the stationary properties of integrable systems. Here we show how a generalized Gibbs ensemble (GGE) can be constructed as the best approximation to the time-dependent density matrix. Our procedure allows for a systematic construction of the GGE by a constrained minimization of the distance between the latter and the true state. Moreover, we show that the entropy of the GGE is a direct measure for the quality of the approximation. We apply our method to a quenched hard core Bose gas. Whereas a correlated GGE properly describes all stationary nonlocal correlations, a simple harmonic GGE is sufficient to completely describe reduced local states.
authors.affiliation: TQC, Universiteit Antwerpen, Antwerpen, B-2610, Belgium and Department of Physics, Boston University, Boston, Massachusetts 02215, USA.
authors.forename: Dries
authors.initials: D
authors.lastname: Sels
authors.affiliation: TQC, Universiteit Antwerpen, Antwerpen, B-2610, Belgium.
authors.forename: Michiel
authors.initials: M
authors.lastname: Wouters