Regensburg 2013 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 58: Poster Session Transport & Matter at Low Temperature
TT 58.35: Poster
Donnerstag, 14. März 2013, 15:00–19:00, Poster D
Non-perturbative stochastic method for driven quantum impurity systems — •Peter Orth1 and Karyn Le Hur2 — 1Institute for Theory of Condensed Matter, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe — 2Center for Theoretical Physics, Ecole Polytechnique, CNRS, 91128 Palaiseau Cedex, France
We discuss a numerically exact method for investigating the real-time dissipative dynamics of quantum impurities embedded in a macroscopic environment beyond the weak-coupling limit. We focus on the spin-boson Hamiltonian that describes a two-level system interacting with a bosonic bath of harmonic oscillators. Starting from the real-time Feynman-Vernon path integral, we derive an exact stochastic Schrödinger equation that allows to compute the full spin density matrix and spin-spin correlation functions beyond weak coupling. We present an analogy between the dissipative dynamics of a quantum spin and that of a classical spin in a random magnetic field. This analogy is used to recover the well-known Non- Interacting-Blip-Approximation (NIBA) in the weak-coupling limit. As interesting applications of our method, we explore the non-Markovian effects of the initial spin-bath preparation on the dynamics of the coherence σx(t) and of σz(t) under a Landau-Zener sweep of the bias field. We also compute to a high precision the asymptotic long-time dynamics of σz(t) without bias and demonstrate the wide applicability of our approach by calculating the spin dynamics at non-zero bias and different temperatures.