Theory of controlling stochastic resonance

The concept of controlling stochastic resonance has been recently introduce d [L. Gammaitoni et al., Phys. Rev. Lett. 82, 4574 (1999)] to enhance or su ppress the spectral response to threshold-crossing events triggered by a ti me-periodic signal in background noise. Here, we develop a general theoreti cal framework, based on a rate equation approach. This generic two-state th eory captures the essential features observed in our experiments and numeri cal simulations.