JOINT ICTP/SISSA STATISTICAL PHYSICS SEMINAR: "Effective thermal dynamics,following a quantum quench in a spin chain"

[statphys]

JOINT ICTP/SISSA STATISTICAL PHYSICS SEMINAR

Tuesday, 19 May 2009   -    12:30 hrs

Lecture Room D
SISSA Main Building

Davide ROSSINI
(S.I.S.S.A. - Trieste)

"Effective thermal dynamics
following a quantum quench in a spin chain"

Abstract
Recent experiments with ultracold atomic gases have triggered a great 
deal of interest in some fundamental aspects of the non-equilibrium 
dynamics of strongly correlated quantum systems. In particular, they 
raised an intense discussion on the general relation between system 
integrability and thermalization in the long-time dynamics of such systems.

Instead of focusing on the asymptotic values of significant observables, 
we take a rather different perspective and study the dependence of the 
intrinsic dynamical time-scale on the initial state. We do this by 
considering the quantum Ising chain: we drive it out-of-equilibrium by 
abruptly quenching the transverse field. We focus on the onsite 
autocorrelation function of the order parameter, extracting the phase 
coherence time from its asymptotic decay. This phase coherence time is 
shown to be determined only by the final Hamiltonian gap, and an 
effective temperature which depends on the energy of the initial state 
after the quench. Moreover, the dependence of the coherence time on the 
effective temperature fairly agrees with that obtained in thermal 
equilibrium as a function of the equilibrium temperature. These results 
pertain to the Ising universality class, while the integrability of the 
model seems not to be crucial.