Chaos and bifurcation in Josephson voltage-controlled oscillators

We report the performance of a Josephson Voltage-controlled oscillator consisting of a tunnel junction shunted by a small inductor in series with a small bias resistor (a resistive SQUID circuit). The circuit displayed regions of stability, bifurcation, and chaos as a function of bias conditions and circuit parameters. We measured narrow band coupled power levels of 25 pW in the fundamental mode and 50 pW in the first subharmonic mode over a 10% frequency band at approximately 9 GHz. Linewidths were dominated by the thermal noise of the bias resistor. These results are in qualitative agreement with numerical simulations, which also show progressive bifurcations from fundamental to chaotic trajectories.