Stochastic resonance: noise enhanced order

Stochastic resonance (SR) is one of the bright examples of noise-induced transitions in nonlinear systems driven by an information signal and noise simultaneously. In the regime of SR some characteristics of the information signal (amplification, signal-to-noise ratio, coherence and ordering degree etc.) at the output of the system are substantially improved at a certain optimal noise level. SR is realized only in nonlinear systems for which it is possible to control one of the characteristic time scales by varying the noise intensity. In the present review a physical mechanism and methods of the theoretical description of SR are discussed. The features of SR determined by the information signal structure, noise statistics and the properties of the concrete systems exhibiting the SR effect are studied. A nontrivial phenomenon of stochastic synchronization defined as the locking of the instantaneous phase and switching frequency of a bistable system by an external periodic force is analyzed in detail. Stochastic synchronization is explored in single and coupled bistable oscillators including ensembles. The effects of SR and stochastic synchronization of the ensembles of stochastic resonators are investigated both without coupling between the elements and in the case of their interaction. SR is considered in dynamical and nondynamical (threshold) systems. The SR effect is analyzed from the viewpoint of information and entropy signal characteristics that determine the order and self-organization degree of the system. The application of the SR concept in order to explain the results of a series of biological experiments is discussed.