Regensburg 2010 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 27: CE: Poster Session

TT 27.59: Poster

Wednesday, March 24, 2010, 14:00–18:00, Poster D1

Quantum Dynamics of a spin-boson system close to a classical phase transition — •Lutz Bakemeier, Andreas Alvermann, and Holger Fehske — Institut für Physik, Universität Greifswald, Deutschland

The Rabi model of a spin 1/2 coupled to a harmonic oscillator features a classical phase transition in the limit of zero oscillator frequency. While no phase transition exists in the full quantum model, the existence of the classical transition leads to interesting dynamics in the 'adiabatic limit' of small oscillator frequency. We begin with the characterization of the groundstate. From a simple variational ansatz, which is in good quantitative agreement with exact data, we deduce the relevant effects at different ratios of spin and oscillator frequency. Only at large oscillator frequency the model properties are explained through simple renormalization of the spin dynamics. Based on the groundstate characterization we discuss the Rabi quantum dynamics, with particular emphasis on the signatures of the classical phase transition, e.g. a lock-in of spin and oscillator dynamics. Our contribution shows that the Rabi model is a kind of generic model for the physics of different time-scales. The relevance for general spin-boson models and the connection to a general concept of 'polaron' physics are discussed.