Non-equilibrium stochastic thermodynamics of Brownian particle in an active bath

Abstract

Particles kicked by external forces to produce mobility distinct from thermal diffusion are an iconic feature of the active matter problem. One example is the passive particles in the bath of active particles, such as swimming bacteria. In this case, the fluctuation of the particle position is influenced by the thermal and the active fluctuations simultaneously. Here, we map this onto a minimal model for experiment and theory covering the wide time and length scales of usual active matter systems. A particle`s diffusion perturbed by a programmable harmonic potential (optical trap) is captured. It gives a time correlated active kicks with a random interval following the Poisson process. The model’s generic simplicity allows us to find conditions for which displacements are Gaussian (or not), how diffusion is perturbed (or not) by kicks, and quantifying heat dissipation to maintain the non-equilibrium steady state in an active bath. The model proposed in the work successful reproduces the experimental results, as shown on example of the tracer mobility in an active bath of swimming algal cells. It can be used as a stochastic dynamic simulator for Brownian objects in various active baths without mechanistic understanding, owing to the generic framework of the protocol.