Quantum and classical resonant escapes of a strongly driven Josephson junction

Abstract

The properties of phase escape in a dc superconducting quantum interference device ͑SQUID͒ at 25 mK, which is well below quantum-to-classical crossover temperature T cr , in the presence of strong resonant ac driving have been investigated. The SQUID contains two Nb/ Al-AlO x / Nb tunnel junctions with Josephson inductance much larger than the loop inductance so it can be viewed as a single junction having adjustable critical current. We find that with increasing microwave power W and at certain frequencies and / 2, the single primary peak in the switching current distribution, which is the result of macroscopic quantum tunneling of the phase across the junction, first shifts toward lower bias current I and then a resonant peak develops. These results are explained by quantum resonant phase escape involving single and two photons with microwave-suppressed potential barrier. As W further increases, the primary peak gradually disappears and the resonant peak grows into a single one while shifting further to lower I. At certain W, a second resonant peak appears, which can locate at very low I depending on the value of . Analysis based on the classical equation of motion shows that such resonant peak can arise from the resonant escape of the phase particle with extremely large oscillation amplitude resulting from bifurcation of the nonlinear system. Our experimental result and theoretical analysis demonstrate that at T Ӷ T cr , escape of the phase particle could be dominated by classical process, such as dynamical bifurcation of nonlinear systems under strong ac driving.

Resonant phase escape in Bi2Sr2CaCu2O8+δsurface intrinsic Josephson junctions

“…The above results demonstrate that the quantum picture of the resonant phase escape with barrier suppression well interprets the experimental observations in figures 3, 4, 6 and 8 for the Bi2212 SIJJ. These results are similar to those observed previously in both the conventional Josephson junctions [27,29,38] and the IJJs [14,17], and differ from the reports in [7][8][9] in that they are accompanied by certain barrier suppression and equation (4) is not satisfied.…”

“…We measured P(I ) using the time-of-flight technique, as described in our previous work [15,16,29,30]. The sample was enclosed in a copper box that was anchored to the mixing chamber (MXC) of the dilution refrigerator.…”

Investigation of low temperature quantum crossover in Josephson junctions

“…What this shows is that for an MQT process, there is a crossover temperature T cr , whereas for an enhanced MQT process there is a corresponding enhanced crossover temperature eT cr . As the figure illustrates, this enhancement of the [9]. Circles (green): simulation results for SCD peak positions versus temperature with TA and MQT operating concurrently (as in the lower panel of Figure 1 ).…”

“…We now analyze the experiments presented in [9]. Figure 2 in [9] (also repeated in [18]) includes a plot of SCD peak positions as a function of junction temperature.…”

“…Previously, we employed data from the experiment of Yu et al [9] as a basis of assessing the predictions of a non-quantum device model from SCD peaks. Here we again use that same set of data, as well as results in the seminal work of Voss and Webb [6], but now exclusively from the perspective of macroscopic quantum device models.…”