A perturbation theory for multi-time correlation functions in open quantum systems

• URL: http://arxiv.org/abs/2502.19137v2
• Date: Tue, 11 Mar 2025 13:44:11 GMT
• Title: A perturbation theory for multi-time correlation functions in open quantum systems
• Authors: Piotr Szańkowski,
• Abstract summary: We extend the scope of open quantum system theory by developing a systematic theory for computing multi-time correlation functions.<n>For closed systems, such correlations are well-defined, even though knowledge of the system's state alone is insufficient to determine them fully.
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• 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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