Experimental evidence of the failure of Jarzynski equality in active baths

Abstract

Most natural and engineered processes, such as biomolecular reactions, protein folding, and population dynamics, occur far from equilibrium and, therefore, cannot be treated within the framework of classical equilibrium thermodynamics. The Jarzynski equality holds the promise to calculate the free-energy difference between two states from the Boltzmann-weighted statistics of the irreversible work done along trajectories arbitrarily out of equilibrium. This equality is the subject of intense activity. However, the applicability of the Jarzynski equality to systems far from equilibrium such as living matter has not been investigated yet. We present an experimental test of the Jarzynski equality predictions on a paradigmatic physical model, i.e. a Brownian particle held in an optical potential, coupled either to a thermal bath or to an active bath. While in the thermal bath we find that the Jarzynski equality correctly retrieves the free-energy difference from nonequilibrium measurements, in the active bath the Jarzynski equality fails because of the presence of non-Boltzmann statistics. We corroborate our experimental findings with theoretical arguments and numerical simulations.