Flux amplification using stochastic superconducting quantum interference devices

Abstract

The flux change δ Φ through a bistable superconducting quantum interference device has been measured in the presence of thermally induced switching (with rate Γ) versus δ Φ x , the change in the applied flux. For small δ Φ x , δ Φ is proportional to δ Φ x with a measured flux gain g, depending on the temperature, barrier height, and frequency Ω, with a maximum of about 16. In agreement with theories of periodically driven stochastic bistable systems,g(Ω) is nearly frequency independent up to Γ and is proportional to Ω−1 for Ω≫Γ. For larger amplitude signals, harmonic generation has been measured in the adiabatic limit (Ω≪Γ) and found to be in good agreement with theory. Possible applications of this system for flux measurement are discussed.