Research on chaos dynamic characteristics of multiple interactive Josephson junction application

Three shunted Nb/Al–AlOx/Nb Josephson junctions (JJs) were fabricated, and the current–voltage (I–V) curve of JJs was measured at 4.2 K. The complex dynamical behaviors of the Josephson junctions (JJs) with parallel and series connection were investigated based on the resistive–capacitive–inductive shunted junction (RCLSJ) model with normalized characteristics parameters βC = 1.4 and βL1 = 2.5393. Numerical simulations revealed that specific features in the experimental I–V characteristic of these devices are a DC phenomenon of complex AC dynamic behavior. The influence of varied critical currents on the I–V characteristics of JJs and the details of intrinsic junction resonances were simulated based on the RCLSJ model. For the parallel-connected JJs with βC = 1.7 and βL1 = 1.9, the grouped critical currents iC1 = iC3 = 1 and iC2 = 1.1 would excite the controllable resonant state position of the paralleled JJs. For the JJs in series with βC = 1.7 and βL1 = 1.9, the unified Shapiro step can be constructed when the normalized critical current difference is within 3%, which reveals intrinsic junctions generally hard to generate unified Shapiro step. The normalized critical boundaries of the chaos state and the periodic dynamic state are proposed, with the chaos state occurring at normalized inductance values above three. The model of five JJs in series with and without irradiation was also simulated. The JJs have two groups of critical currents; therefore, two voltage jumps could be observed in the I–V curves with fixed inductance and capacitance. Under irradiation, two first-order Shapiro steps appeared in the I–V curves at voltages of 2 and 3. In addition, as critical current of each JJ increases, the current steps also increased in an ordered manner.