Abstract

We consider a d-dimensional quantum system that is prepared in a general initial state that satisfies the cluster decomposition principle and evolves under a noninteracting Hamiltonian, a setup that can be realised by a quantum quench. We show that, in the thermodynamic limit, the dominant large time behaviour of any multipoint correlation function can be expressed in terms of the (conserved) occupations of momentum modes of the system, for any spatial dimension d and independently of whether the system tends to a stationary state or not. This result is an extension of the GGE hypothesis, which is conjectured to describe the equilibrium properties of 1d integrable systems after a quantum quench. We further show that the same reasoning suggests a precise criterion for determining which conserved charges must be included in the GGE of a general 1d integrable model.