Noise-enhanced phase locking in a stochastic bistable system driven by a chaotic signal

We study the dynamics of an overdamped bistable system driven simultaneously by noise and a chaotic input signal. The effect of synchronization of switchings in a stochastic bistable system by a subthreshold chaotic signal is found and described in terms of the theory of phase synchronization. Using the two different definitions of the instantaneous phase of stochastic and chaotic oscillations, we show explicitly the effect of noise-enhanced phase locking both for coherent and for broadband chaotic input signals. The quantitative analysis of this effect has shown that the degree of phase coherence estimated by means of the effective diffusion constant is maximal in some range of noise intensities. Moreover, there is a synchronization region on the parameter plane "amplitude of chaotic signal-noise intensity" in which the phases and mean frequencies of an input signal and of response are locked. [S1063-651X(99)09301-0].