Pinch resonances in a radio-frequency-driven superconducting-quantum-interference-device ring-resonator system.

In this paper we present experimental data on the frequency domain response of a superconducting-quantum-interference-device ring (a Josephson weak link enclosed by a thick superconducting ring) coupled to a radio frequency tank circuit resonator. We show that with the ring weakly hysteretic the resonance line shape of this coupled system can display opposed fold bifurcations that appear to touch (pinch off). We demonstrate that for appropriate circuit parameters these pinch off line shapes exist as solutions of the nonlinear equations of motion for the system.