title: Diverging equilibration times in long-range quantum spin models.
abstract: The approach to equilibrium is studied for long-range quantum Ising models where the interaction strength decays like r(-α) at large distances r with an exponent α not exceeding the lattice dimension. For a large class of observables and initial states, the time evolution of expectation values can be calculated. We prove analytically that, at a given instant of time t and for sufficiently large system size N, the expectation value of some observable <A>(t) will practically be unchanged from its initial value <A>(0). This finding implies that, for large enough N, equilibration effectively occurs on a time scale beyond the experimentally accessible one and will not be observed in practice.
authors.affiliation: National Institute for Theoretical Physics (NITheP), Stellenbosch 7600, South Africa. kastner@sun.ac.za
authors.forename: Michael
authors.initials: M
authors.lastname: Kastner