  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.
