Issue 36, 2022

Passive probe particle in an active bath: can we tell it is out of equilibrium?

Abstract

We study a passive probe immersed in a fluid of active particles. Despite the system's non-equilibrium nature, the trajectory of the probe does not exhibit non-equilibrium signatures: its velocity distribution remains Gaussian, the second fluctuation dissipation theorem is not fundamentally violated, and the motion does not indicate breaking of time reversal symmetry. To tell that the probe is out of equilibrium requires examination of its behavior in tandem with that of the active fluid: the kinetic temperature of the probe does not equilibrate to that of the surrounding active particles. As a strategy to diagnose non-equilibrium from probe trajectories alone, we propose to examine their response to a small perturbation which reveals a non-equilibrium signature through a violation of the first fluctuation dissipation theorem.

Graphical abstract: Passive probe particle in an active bath: can we tell it is out of equilibrium?

Article information

Article type
Paper
Submitted
04 Jul 2022
Accepted
26 Aug 2022
First published
29 Aug 2022

Soft Matter, 2022,18, 6965-6973

Passive probe particle in an active bath: can we tell it is out of equilibrium?

J. Shea, G. Jung and F. Schmid, Soft Matter, 2022, 18, 6965 DOI: 10.1039/D2SM00905F

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