Fluctuation Theorem for Quasi-Integrable Systems

A Fluctuation Theorem (FT), both Classical and Quantum, describes the large-deviations in the approach to equilibrium of an isolated quasi-integrable system. Two characteristics make it unusual: (i) it concerns the internal dynamics of an isolated system without external drive, and (ii) unlike the usual FT, the system size, or the time, need not be small for the relation to be relevant, provided the system is close to integrability. As an example, in the Fermi-Pasta-Ulam chain, the relation gives information on the ratio of probability of death to resurrection of solitons. For a coarse-grained system the FT describes how the system `skis' down the (minus) entropy landscape: always descending but generically not along a gradient line.