Josephson Vortex Qubit based on a Confocal Annular Josephson Junction

TL;DR

This paper presents the development and experimental validation of a Josephson vortex qubit using a confocal annular Josephson junction, demonstrating a tunable double-well potential for quantum information processing.

Contribution

It introduces a novel vortex qubit design based on a confocal annular junction with a tunable double-well potential, combining theoretical modeling and experimental validation.

Findings

Successful creation of a robust, tunable double-well vortex potential.

Experimental demonstration of vortex state manipulation via magnetic fields.

Reliable vortex state readout through depinning current measurement.

Abstract

We report theoretical and experimental work on the development of a Josephson vortex qubit based on a confocal annular Josephson tunnel junction (CAJTJ). The key ingredient of this geometrical configuration is a periodically variable width that generates a spatial vortex potential with bistable states. This intrinsic vortex potential can be tuned by an externally applied magnetic field and tilted by a bias current. The two-state system is accurately modeled by a one-dimensional sine-Gordon like equation by means of which one can numerically calculate both the magnetic field needed to set the vortex in a given state as well as the vortex depinning currents. Experimental data taken at 4.2K on high-quality Nb/Al-AlOx/Nb CAJTJs with an individual trapped fluxon advocate the presence of a robust and finely tunable double-well potential for which reliable manipulation of the vortex state has been classically demonstrated. The vortex is prepared in a given potential by means of an externally applied magnetic field, while the state readout is accomplished by measuring the vortex-depinning current in a small magnetic field. Our proof of principle experiment convincingly demonstrates that the proposed vortex qubit based on CAJTJs is robust and workable.