Abstract

We explore how active matter in a non-equilibrium steady state can autonomously deliver mechanical work against a constant mechanical force or torque. For this purpose, we consider systems that contain one or several active components and a single passive component that is asymmetric in its geometrical shape or its interactions. Generally, one expects that such an asymmetry leads to a persistent, directed current in the passive component, which can be used for the autonomous extraction of work. We validate this expectation for a minimal model featuring an active and a passive particle on a one-dimensional lattice and identify thermodynamically consistent measures for the efficiency of the conversion of isotropic activity to directed work. For systems with continuous degrees of freedom, work cannot be extracted using a one-dimensional geometry under quite general conditions. We show which two-dimensional shapes of the passive particle are best suited for the extraction of work. Approximating their effect on the dynamics of the particles leads to analytical results for the power and efficiency. A mean field approach reveals that the interaction with the passive particle can mediate cooperativity between otherwise non-interacting active particles, leading to an enhanced efficiency.