Regensburg 2016 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 23: Quantum Dynamics, Decoherence and Quanten Information

DY 23.2: Talk

Tuesday, March 8, 2016, 14:15–14:30, H48

Diagrammatic description of a quantum system coupled to strong noise — •Michael Marthaler and Juha Leppäkangas — Karlsruhe Institute of Technology

We study a system-bath description in the strong coupling regime, where it is not possible to derive a master equation for the reduced density matrix by a direct expansion in the system-bath coupling. A particular example is a bath with significant spectral weight at low frequencies. Through a unitary transformation it can be possible to find a more suitable small expansion parameter. Within this approach we construct a formally exact expansion of the master equation on the Keldysh contour. The lowest-order expansion is similar to the so-called P(E)-theory or non-interacting blip approximation (NIBA). The analysis of the higher-order contributions shows that there are two different classes of higher-order diagrams. We study how the form of the spectral function affects their convergence.