ZERO-DISPERSION STOCHASTIC RESONANCE IN A MODEL FOR A SUPERCONDUCTINGQUANTUM INTERFERENCE DEVICE

It is demonstrated that the signal-to-noise ratio for a weak periodic signal in a superconductive loop with a Josephson junction (a supercon ducting quantum interference device, or SQUID) can be substantially en hanced, over a wide range of frequencies, by the addition of noise. Th is manifestation of zero-dispersion stochastic resonance (ZDSR) is sho wn to occur for a wide variety of loop parameters and signal frequenci es. Unlike most earlier examples of stochastic resonance, ZDSR does no t depend on fluctuational transitions between coexisting stable states . Rather, it exploits the noise-enhanced susceptibility that arises in underdamped nonlinear oscillators for which the oscillation eigenfreq uency possesses one or more extrema as a function of energy. The pheno menon is investigated theoretically, and by means of analog and digita l simulations. It is suggested that ZDSR could be used to enhance the sensitivity of radio-frequency SQUIDs and other SQUID-based devices. I n the course of the work, two additional useful results were obtained: (a) an asymptotic expression describing ZDSR for the general case in the Limit of weak dissipation; (b) a method for the numerical calculat ion of fluctuation spectra in bistable or multistable underdamped syst ems.