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Physics of Particles and Nuclei

Quantum transport: Self-consistent approximations

Dmitry N. Voskresensky

Published Nov 22, 2008• 0 citations
Publisher

Abstract

Functional methods: Generating Φ {ϕ, G } functional of Baym on Schwinger-Keldysh contour; symmetries and conservation laws; thermodynamic consistency. (See [1]. Renormalization scheme can be found in [2].) Generalized kinetic approach: gradient approximation. (See [3]. Gradient expansion diagram technique see in [4].) Some helpful examples. (See [5].)

DOI
10.1134/s1063779608070393

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The work fluctuation theorem (FT) is a symmetry connecting the moment generating functions (MGFs) of the work extracted in a given process and in its time-reversed counterpart. We show that, equivalently, the FT for work in isolated quantum systems can be expressed as an invariance property of a modified Keldysh contour. Modified contours can be used as starting points of perturbative and path integral approaches to quantum thermodynamics, as recently pointed out in the literature. After reviewing the derivation of the contour-based perturbation theory, we use the symmetry of the modified contour to show that the theory satisfies the FT at every order. Furthermore, we extend textbook diagrammatic techniques to the computation of work MGFs, showing that the contributions of the different Feynman diagrams can be added to obtain a general expression of the work statistics in terms of a sum of independent rescaled Poisson processes. In this context, the FT takes the form of a detailed balance condition linking every Feynman diagram with its time-reversed variant. In the second part, we study path integral approaches to the calculation of the MGF, and discuss how the arbitrariness in the choice of the contour impacts the final form of the path integral action. In particular, we show how using a symmetrized contour makes it possible to easily generalize the Keldysh rotation in the context of work statistics, a procedure paving the way to a semiclassical expansion of the work MGF. Furthermore, we use our results to discuss a generalization of the detailed balance conditions at the level of the quantum trajectories.