STOCHASTIC RESONANCE

Stochastic Resonance (SR) is a term given to an effect which is manifest in multi stable nonlinear systems driven simultaneously by noise and a weak periodic function, whereby the information flow through the system, in the form of the frequency of the periodic function, is assisted by the noise. For every frequency of the modulation, the information flow is optimum for a specific noise intensity, that is for a specific Kramers transition rate, hence the term resonance. Two physical quantities which characterize the response of such a system have been the objects of a flurry of recent experimental and theoretical activity: the Fourier transform, or auto correlation function of the appropriate state variable, and the probability density of the residence or escape times. The former have been used to obtain the power spectra and hence the signal-to-noise ratios of the response, while the latter directly reflect the rates and symmetry properties of the system. Calculation of these quantities pose specific problems for theorists characteristic of non stationary Fokker-Planck systems. In this paper, I will briefly review the recent activity and include some remarks on the historical foundations of SR.