Fluctuation theorem for transport in mesoscopic systems

The fluctuation theorem for currents is applied to several mesoscopic systems on the basis of Schnakenberg's network theory, which allows one to verify its conditions of validity. A graph is associated with the master equation ruling the random process and its cycles can be used to obtain the thermodynamic forces or affinities corresponding to the nonequilibrium constraints. This provides a method of defining the independent currents crossing the system in nonequilibrium steady states and to formulate the fluctuation theorem for the currents. This result is applied to out-of-equilibrium diffusion in a chain, to a biophysical model of ion channels in a membrane, and to electronic transport in mesoscopic circuits made of several tunnel junctions. In this latter, we show that the generalizations of Onsager's reciprocity relations to the nonlinear response coefficients also hold.