Regensburg 2016 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 64: Correlated Electrons: Nonequilibrium Quantum Many-Body Systems 1
TT 64.12: Vortrag
Donnerstag, 10. März 2016, 12:30–12:45, H22
How to guarantee complete positivity in approximations to open-system dynamics: Kraus theorem on the Keldysh contour — •Viktor Reimer1,2 and Maarten Rolf Wegewijs1,2,3 — 1Peter Grünberg Institut, Forschungszentrum Jülich, 52425 Jülich, Germany — 2JARA-Fundamentals of Future Information Technology — 3Institute for Theory of Statistical Physics, RWTH Aachen, 52056 Aachen, Germany
A fundamental problem in the theory of open quantum systems is how to guarantee that the time-evolution within a nontrivial approximation scheme results in a valid physical mixed state.
Spurred by a crucial work of van Wonderen and Suttorp [1], we present a general framework based on the Kraus representation of the exact reduced system dynamics, in which positivity-, hermicity- and trace-preserving approximations can be systematically formulated. We relate the Kraus operators to the standard real-time Keldysh diagrammatic expansion and identify precisely which partial resummations of such diagrams strictly enforce complete positivity of the density operator. This allows the derivation of time-nonlocal quantum master equations with approximate kernels that strictly preserve complete positivity.
[1] A. J. van Wonderen and L. G. Suttorp, EPL 102, 60001 (2013)