Superconducting single-junction interferometers with small critical currents

Abstract

A simple theory of the superconducting single‐junction interferometer (ac Squid) becomes possible if the critical current of the single junction is small relative to Φ₀/L_R, where Φ₀=h/2e is one flux quantum and L_R is the inductance of the interferometer loop. This theory predicts a magnetic flux sensitivity which has the same dependence on interferometer parameters as the existing theories for higher critical currents. In contrast to those theories, however, the present theory predicts that the maximum flux sensitivity will be achieved off resonance. Theoretical predictions for comparison with experiment are displayed as a function of the normalized difference between the operating frequency ω and the resonant frequency ω₀.