Stochastic and parametric amplification of narrow-band signals in a single-junction SQUID interferometer

The features of the response of a single-junction superconducting quantum interferometer to a low-frequency harmonic signal in the presence of noise and a high-frequency electromagnetic field are investigated through numerical solution of the equations of motion. It is shown that in this situation a system described by a double-well potential will display stochastic-parametric amplification of weak harmonic signals owing to the cooperative effects of noise and the high-frequency field. The gain is a nonmonotonic function of the amplitude of the high-frequency field and the variance of the noise flux and passes through a maximum. A detailed numerical analysis of the dependence of the gain on the noise intensity and on the frequency and amplitude of the high-frequency field is carried out in the stochastic, parametric, and stochastic-parametric amplification regimes. It is shown that at optimal amplitude of the high-frequency field the gain for a weak harmonic signal reaches rather high values (10-30). The specific properties of stochastic-parametric amplification are discussed, and the possible applications of this effect for constructing input circuits of detectors based on SQUIDs with registration of weak narrow-band information signals are considered