Berlin 2005 – scientific programme
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TT: Tiefe Temperaturen
TT 8: Posters Transport
TT 8.46: Poster
Friday, March 4, 2005, 14:00–18:00, Poster TU C
Quantum phase transitions in a 2-qubit system — •Henryk Gutmann1, Frank Wilhelm1, and Gergely Zaránd2 — 1Department für Physik and CeNS, LMU, 80333 München — 2Department of Theoretical Physics, Budapest University of Technology and Economics, H-1521 Budapest, Hungary
For describing local as well as common decoherence effects we investigate
a setup of two coupled spins influenced by two local bosonic baths as well
as a common one.
Here we are interested to go beyond the usual weak coupling regime,
as we want to focus on the transition from quantum mechanical behaviour to
classical localization of the spins, as well as the emergence and
disappearance of entanglement.
We start with a quite generic two-spin generalization of the spin-boson
model, i.e. where the environmentral influences, the spin interactions
and the spin Hamiltonian do not commute with each other.
In order to eliminate the environmental Hamiltonian terms we unitarily
transfer the spin-boson Hamiltonian onto the anisotropic Kondo model,
using a technique given in Ref.[1].
Therefrom we derive scaling equations in first order perturbation theory.
Considering the corresponding fixed point Hamiltonian we receive first
qualitative insights in the different dissipative phase regimes.
To get more reliable results we present higher order scaling equations
by applying operator product expansions on the generated
products of the renormalized spin couplings.
[1]: T.A. Costi and G. Zaránd, Phys. Rev. B 59, 12398 (1999).