Resonances in symmetric Josephson interferometers

A simple analytical theory is presented which calculates the current due to self-induced resonances in symmetric two-junction Josephson interferometers as a function of voltage, control current, and damping. Experimental measurements of interferometer I-V curves near a resonance and of peak resonance amplitudes as a function of control current were carried out and found to agree with the theory. The existence of a negative-resistance region in the I-V curves of lightly damped, current-biased interferometers is predicted and experimentally verified. The theory allows accurate determination of the resonant voltage and the interferometer damping from experimental I-V curves.