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Dynamical Behavior of the Dissipative Two-State System

Klaus Voelker
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Abstract

We investigate the dynamical correlation function of a quantum-mechanical two-state system which is coupled to a bosonic heat bath, utilizing the equivalence between the spin-boson Hamiltonian and the 1/r^2 Ising model. The imaginary-time correlation function is calculated by Monte-Carlo simulations on the Ising system and then continued to real time by a Pade approximation. In the unbiased system, the transition from oscillatory to strongly damped behavior is found to occur at a coupling strength close to alpha = 1/2. The biased system favors coherent relaxation and displays a significantly larger crossover value alpha_c. We introduce the quasiparticle picture to describe the relevant behavior at intermediate time scales. Within this approximation, we map out phase diagrams for the unbiased and biased systems.

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Klaus Voelker. 1998-07-19. Dynamical Behavior of the Dissipative Two-State System. https://doi.org/10.1103/physrevb.58.1862

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