Power spectra of noise-induced hopping between two overlapping Josephson steps

Abstract

We have studied the power spectra measured from an electronic analog of a driven Josephson junction. The frequency of the ac drive is 1.1 times the plasma frequency of the Josephson analog. At this frequency, the I-V curve of a noise-free simulation shows a region of overlap between the zeroth and the (2/3 Josephson steps. Adding noise to the simulation causes the system to switch between the two steps which forms a noisy ramp similar to that seen from a Josephson junction driven at 419 GHz. The power spectra of the switching voltage measured from the analog are essentially Lorentzian, indicating that the hopping time is much shorter than the lifetimes of the two states. By measuring the noise power density at zero frequency and the 3-dB roll-off frequency of the Lorentzian spectrum, we can deduce the lifetimes of the two states. The exponential dependence of the lifetimes on the noise level indicates that this hopping is similar to a thermally activated hopping over an energy barrier, which characterizes the global stability of the attractors under finite perturbations.

Source-reported materials — not catalogue approval

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