Probing the limits of effective temperature consistency in actively driven systems

TL;DR

This study examines the validity of the effective temperature concept in an active, nonequilibrium system by comparing different measurement methods, revealing conditions of consistency and fundamental limits.

Contribution

It provides an experimental assessment of the robustness and limitations of effective temperature definitions in active matter systems.

Findings

Effective temperature measurements are consistent under certain conditions.

Discrepancies arise in specific regimes, indicating limits of thermodynamic analogy.

The work delineates the boundaries of applying equilibrium concepts to active systems.

Abstract

We investigate the thermodynamic properties of a single inertial probe driven into a nonequilibrium steady-state by random collisions with self-propelled active walkers. The probe and walkers are confined within a gravitational harmonic potential. We evaluate the robustness of the effective temperature concept in this active system by comparing values of distinct, independently motivated definitions: a generalized fluctuation-dissipation relation, a kinetic temperature, and a work fluctuation relation. Our experiments reveal that, under specific conditions, these independent measurements yield a remarkably consistent effective temperature over a wide range of system configurations. Furthermore, we also identify regimes where this consistency breaks down, which delineates the fundamental limits of extending equilibrium-like thermodynamic concepts to athermal, actively driven systems.