We show that a conservative system of a pair of coupled incoherent nonlinear waves exhibits huge oscillations of coherence, which are characterized by a recurrent transfer of noise fluctuations between the coupled waves. This sustained oscillatory behavior is in contradiction with the expected irreversible evolution towards equilibrium. As a consequence, the process of coherence transfer is characterized by a reduction of nonequilibrium entropy, which violates the $H$ theorem of entropy growth inherent to the kinetic theory.

• Received 28 July 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.013905