Fluctuation-dissipation of an active Brownian particle under confinement

This study aims to address the question of fluctuation-dissipation relationship in a non-equilibrium system comprising active Brownian particles. Specifically, the fluctuation power spectral densities (PSD) of an Induced-ChargeElectrophoresis-driven metallic Janus particle in an optical trap was measured and compared the PSDs to that of nondriven particles. Unlike the PSDs of Brownian particles where there exists only one characteristic frequency, the PSDs of active Brownian particles have two with the second frequency characterized by the particles’ rotation diffusion. Energy dissipation of such particles, defined as the integrated PSDs were examined. Finally, Effective temperatures defined by various means, including the probability distribution of the particle's positions in the trap, and the zero-frequency limit of the fluctuation power spectral densities, are examined for the active Brownian particles.