Switching Current Measurements in Josephson Rings

TL;DR

This paper investigates the switching current behavior in underdamped Josephson rings, revealing fluxon dynamics and thermal activation effects that influence the switching process.

Contribution

It provides experimental evidence of fluxon diffusion and analyzes switching currents using thermal activation models in Josephson rings.

Findings

Fluxon diffusion observed prior to switching

Switching current affected by temperature and fluxons

Qualitative agreement with thermal activation theory

Abstract

We present switching current measurements in niobium-aluminum oxide-niobium underdamped Josephson rings. Underdamped Josephson rings display hysteretic current-voltage curves which can be characterized by their switching current, the value of applied current at which the junctions switch to the energy-gap voltage. The value of the switching current is strongly affected by temperature and by the presence of fluxons in the system. We observe a very small voltage (0.2 nV) across the ring prior to switching, indicating a low-velocity fluxon diffusion state before the jump to a full running state. In analogy with previous work on single junctions, we analyze the switching current data with the process of thermal activation over a dissipation barrier, where the system switches from a low velocity state to a high velocity state. We find that our data agrees qualitatively with this description, further supporting the observation of fluxon diffusion.