Power production from anisotropic fluctuations

Power production from anisotropic fluctuations: The Brownian gyrator represents the most basic thermodynamic system from which one can extract work by tapping simul- taneously into two heat baths with different temperatures. Specifically, it consists of an overdamped system with two coupled degrees of freedom in an anisotropic temperature field. Whereas the hallmark of the gyrator is a nonequilibrium steady-state curl-carrying probability current, we explore the coupling of this natural gyrating motion with a periodic actuation potential for the purpose of producing power. We show that path-lengths traversed in the manifold of thermodynamic states, measured in a suitable Riemannian metric, represent dissipative losses, while area integrals of a work-density quantify work being extracted. Thus, the maximal amount of work that can be extracted relates to an isoperimetric problem, trading off area against length of an encircling path. We derive an isoperimetric inequality that provides a universal bound on the efficiency of all cyclic operating protocols, and a bound on how fast a closed path can be traversed before it becomes impossible to extract positive work. The analysis presented provides guiding principles for building autonomous engines that extract work from anistropic fluctuations.