# Driven Brownian particle as a paradigm for a nonequilibrium heat bath: Effective temperature and cyclic work extraction

## TL;DR

This paper demonstrates how a driven Brownian particle in a nonequilibrium steady state can serve as a heat bath with a frequency-dependent effective temperature, enabling work extraction from a single reservoir.

## Contribution

It introduces the use of a driven Brownian particle as a nonequilibrium heat bath and shows how it can be used to extract cyclic work, highlighting novel thermodynamic behavior.

## Key findings

- The oscillator thermalizes at the effective temperature across frequencies.
- Work can be cyclically extracted from a single nonequilibrium reservoir.
- The effective temperature concept applies across the entire frequency spectrum.

## Abstract

We apply the concept of a frequency-dependent effective temperature based on the fluctuation-dissipation ratio to a driven Brownian particle in a nonequilibrium steady state. Using this system as a thermostat for a weakly coupled harmonic oscillator, the oscillator thermalizes according to a canonical distribution at the respective effective temperature across the entire frequency spectrum. By turning the oscillator from a passive "thermometer" into a heat engine, we realize the cyclic extraction of work from a single thermal reservoir, which is feasible only due to its nonequilibrium nature.