Regensburg 2025 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 29: Poster: Quantum Dynamics and Many-body Systems

DY 29.2: Poster

Wednesday, March 19, 2025, 15:00–18:00, P4

Quantum Fluctuations Approach to Many-Body Systems for Weak and Strong Coupling — •Erik Schroedter, Jan-Philip Joost, Tim Kalsberger, and Michael Bonitz — CAU, Kiel, Germany

The theoretical description of correlated quantum many-body systems out of equilibrium is a significant challenge across many areas, including condensed matter, ultracold atoms, and dense plasmas. Standard approaches used for their description include the formalisms of reduced density matrices (RDM) and nonequilibrium Green functions (NEGF). However, all approaches suited for the description of nonequilibrium systems are limited in their applicability due to their accuracy or numerical scaling. Here, we present an alternative approach based on fluctuations of field operator products and their correlation functions[1,2]. It is closely related to NEGF and RDM theory and offers an alternative approach to the GW and T-matrix approximations while exhibiting interesting complementary features, such as the capability to simulate many-body effects using stochastic methods[3]. This significantly reduces numerical complexity while preserving accuracy and allows for the description of both weakly and strongly coupled systems. Additionally, this improves numerical stability and allows for direct access to spectral two-particle quantities, such as the density response function or dynamic structure factor.

[1] E. Schroedter, et al., Cond. Matt. Phys. 25, 23401 (2022)

[2] E. Schroedter, and M. Bonitz, CTPP 202400015 (2024)

[3] E. Schroedter, et al., Phys. Rev. B 108, 205109 (2023)

Keywords: nonequilibrium Green functions; quantum fluctuations; stochastic methods