Stochastic Thermodynamic Systems Subject to Anisotropic Fluctuations

Thermodynamics of systems under anisotropic fluctuations—that may represent temperature gradients, differences in concentrations, or non-equilibrium heat baths—are of central importance in our venture to understand certain biological processes. Indeed, life exists far from equilibrium, relying on low entropy states like those found in anisotropic environments. In this chapter, we introduce the basic framework and define quantities of interest such as energy, entropy, heat, or work. We focus on overdamped thermodynamic systems where each degree of freedom interacts with a different temperature bath. We explore the emergence of non-equilibrium steady-states and derive a fluctuation theorem for anisotropic systems. Additionally, we discuss the Brownian gyrator, a minimal thermally anisotropic system known for its torque-generating nonequilibrium steady-state and its several experimental realizations.