%0 Conference Paper
%A Novotny, Mark
%A Jin, Fengping
%A Yuan, Shengjun
%A Miyashita, Seiji
%A De Raedt, Hans
%A Michielsen, Kristel
%T Decoherence and Thermalization at Finite Temperatures for Quantum Systems
%M FZJ-2016-04023
%D 2016
%X We consider a quantum system $S$ with Hamiltonian ${\cal H}_S$ coupled via a Hamiltonian ${\cal H}_{SE}$ to a quantum environment $E$ with Hamiltonian ${\cal H}_E$.  We assume the entirety $S+E$ is in a canonical-thermal state at an inverse temperature $\beta$.   The entirety is a closed quantum system which evolves via the time-dependent Schr{\”o}dinger equation with Hamiltonian ${\cal H}={\cal H}_S+{\cal H}_E+\lambda{\cal H}_{SE}$ where $\lambda$ is the overall strength of the system-environment coupling.  Using both large-scale simulations and perturbation theory calculations in $\lambda$, we have studied a measure $\sigma(t)$ for decoherence and $\delta(t)$ for thermalization of $S$.  We performed large-scale parallel calculations on spin systems with up to $N=40$ spins in the entirety, with both real-time and imaginary-time quantum calculations.  We performed perturbation theory calculations about $\lambda=0$ and fluctuations about the average for the canonical-thermal ensemble, for both $\sigma$ and $\delta$.  We obtained closed form expressions for both $\sigma$ and $\delta$, in terms of the free energies of $S$ and $E$.  Our perturbation theory calculations agree very well with our numerical calculations, at least as long as $\beta\lambda$ is small.
%B 26th IUPAP International conference on Statistical Physics
%C 18 Jul 2016 - 22 Jul 2016, Lyon (France)
Y2 18 Jul 2016 - 22 Jul 2016
M2 Lyon, France
%F PUB:(DE-HGF)24
%9 Poster
%U https://juser.fz-juelich.de/record/811604