Środowiskowe Seminarium z Informacji i Technologii Kwantowych
sala 0.06, ul. Pasteura 5
2025-03-06 (11:15) 
Piotr Szańkowski (IFPAN)
A perturbation theory for multi-time correlations in open systems
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, with its dynamical map methods, the theory provides a flexible and accurate framework for computing expectation values of 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.
[1] arXiv:2502.19137
Hence, with its dynamical map methods, the theory provides a flexible and accurate framework for computing expectation values of 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.
[1] arXiv:2502.19137