BRIEF RESEARCH REPORT article
Front. Phys.
Sec. Statistical and Computational Physics
Volume 13 - 2025 | doi: 10.3389/fphy.2025.1667224
Equilibrium trajectories quantify second order violation of fluctuation dissipation theorem without need of a model
Provisionally accepted
- 1Georg-August-Universität Göttingen, Institut für Theoretische Physik, Göttingen, Germany
- 2Universität Konstanz Fachbereich Physik, Konstanz, Germany
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Quantifying and characterizing fluctuations far away from equilibrium is a challenging task. We discuss and experimentally confirm a series expansion for a driven classical system, relating the different non-equilibrium cumulants of the observable conjugate to the driving protocol. This series is valid from micro-to macroscopic length scales, and it encompasses the fluctuation dissipation theorem. We apply it in experiments of a Brownian probe particle confined and driven by an optical potential and suspended in a nonlinear and non-Markovian fluid. The expansion states that the form of FDT remains valid away from equilibrium for Gaussian observables, up to the order presented. We show that this expansion agrees with the expansion of a known fluctuation theorem up to an unresolved difference regarding moments versus cumulants.
Keywords: fluctuation dissipation theorem, non-equilibrium cumulants, Brownian probe particle, Optical potential, nonlinear fluid, non-Markovian fluid, Worm-like micelles, micellar fluid
Received: 16 Jul 2025; Accepted: 18 Sep 2025.
Copyright: © 2025 Caspers, Krishna Kumar, Bechinger and Krüger. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Juliana Caspers, j.caspers@theorie.physik.uni-goettingen.de
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