Passive particle in an active bath: How 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.

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Cited by in corpus (11)

• Inclusions, Boundaries and Disorder in Scalar Active Matter
• How to define temperature in active systems?
• Dynamical fluctuations of a tracer coupled to active and passive particles
• The fluctuation-dissipation relation holds for a macroscopic tracer in an active bath
• Force renormalization for probes immersed in an active bath
• Effective dynamics and fluctuations of a trapped probe moving in a fluid of active hard discs
• Sorting of binary active-passive mixtures in designed microchannels
• Tracer dynamics in an interacting active bath: fluctuations and energy partition
• Active Ornstein-Uhlenbeck Model for Bacterial Heat Engines
• Probing the limits of effective temperature consistency in actively driven systems
• Minimal dissipation with viscoelastic baths in weakly driven processes