Confocal Annular Josephson Tunnel Junctions with Large Eccentricity

TL;DR

This paper investigates how the eccentricity of confocal annular Josephson tunnel junctions affects vortex potential profiles, depinning mechanisms, and noise influences, with implications for vortex qubit applications.

Contribution

It provides a detailed analysis of the impact of increased eccentricity on vortex dynamics and potential profiles in CAJTJs, extending previous moderate aspect ratio studies.

Findings

Eccentricity significantly alters the vortex potential landscape.

Higher eccentricity leads to more complex depinning behavior.

Temperature and noise effects influence vortex stability and control.

Abstract

Confocal Annular Josephson Tunnel Junctions (CAJTJs) which are the natural generalization of the circular annular Josephson tunnel junctions, have a rich nonlinear phenomenology due to the intrinsic non-uniformity of their planar tunnel barrier delimited by two closely spaced confocal ellipses. In the presence of a uniform magnetic field in the barrier plane, the periodically changing width of the elliptical annulus generates a asymmetric double-well for a Josephson vortex trapped in a long and narrow CAJTJ. The preparation and readout of the vortex pinned in one of the two potential minima, which are important for the possible realization of a vortex qubit, have been numerically and experimentally investigated for CAJTJs with the moderate aspect ratio 2:1. In this work we focus on the impact of the annulus eccentricity on the properties of the vortex potential profile and study the depinning mechanism of a fluxon in more eccentric samples with aspect ratio 4:1. We also discuss the effects of the temperature-dependent losses as well as the influence of the current and magnetic noise.