Pulse and hold strategy for switching current measurements

TL;DR

This paper introduces a pulse-and-hold switching method for Josephson junction detectors, combining theoretical analysis and experiments to optimize switching dynamics in frequency-dependent damping environments.

Contribution

It presents a novel pulse-and-hold technique with experimental validation on superconducting circuits, enhancing understanding of switching behavior under frequency-dependent damping.

Findings

Switching can be modeled by thermal escape with 20 μs pulses.

High-frequency overdamped environment improves switching topology.

Rapid 25 ns pulses reveal non-thermal switching mechanisms.

Abstract

We investigate by theory and experiment, the Josephson junction switching current detector in an environment with frequency dependent damping. Analysis of the circuit's phase space show that a favorable topology for switching can be obtained with overdamped dynamics at high frequencies. A pulse-and-hold method is described, where a fast switch pulse brings the circuit close to an unstable point in the phase space when biased at the hold level. Experiments are performed on Cooper pair transistors and Quantronium circuits, which are overdamped at high frequencies with an on-chip RC shunt. For 20 us switch pulses the switching process is well described by thermal equilibrium escape, based on a generalization of Kramers formula to the case of frequency dependent damping. A capacitor bias method is used to create very rapid, 25 ns switch pulses, where it is observed that the switching process is not governed by thermal equilibrium noise.