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A perturbation theory for multi-time correlation functions in open quantum systems
by Piotr Szańkowski
Submission summary
Authors (as registered SciPost users): | Piotr Szankowski |
Submission information | |
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Preprint Link: | https://arxiv.org/abs/2502.19137v2 (pdf) |
Date submitted: | 2025-03-12 09:40 |
Submitted by: | Szankowski, Piotr |
Submitted to: | SciPost Physics |
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Academic field: | Physics |
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Approach: | Theoretical |
Abstract
Dynamical maps are the principal subject of the open system theory. Formally, the dynamical map of a given open quantum system is a density matrix transformation that takes any initial state and sends it to the state at a later time. Physically, it encapsulates the system's evolution due to coupling with its environment. Hence, the theory provides a flexible and accurate framework for computing expectation values of open system observables. However, expectation values -- or more generally, single-time correlation functions -- capture only the simplest aspects of a quantum system's dynamics. A complete characterization requires access to multi-time correlation functions as well. For closed systems, such correlations are well-defined, even though knowledge of the system's state alone is insufficient to determine them fully. In contrast, the standard dynamical map formalism for open systems does not account for multi-time correlations, as it is fundamentally limited to describing state evolution. Here, we extend the scope of open quantum system theory by developing a systematic perturbation theory for computing multi-time correlation functions.
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