Engineering Double-Well Potentials with Variable-Width Annular Josephson Tunnel Junctions

TL;DR

This paper presents a method to engineer double-well potentials in elliptic annular Josephson tunnel junctions, enabling control of fluxon states for potential quantum computing applications.

Contribution

It introduces a simple technique to create and manipulate double-well potentials for fluxons in non-uniform Josephson junctions using magnetic fields and current ramps.

Findings

Controlled double-well potentials for fluxons are achievable.

The potential properties depend on junction eccentricity and electrical parameters.

Quantum effects like energy level discretization and tunneling are addressed.

Abstract

Long Josephson tunnel junction are non-linear transmission lines that allow propagation of current vortices (fluxons) and electromagnetic waves and are used in various applications within superconductive electronics. Recently, the Josephson vortex has been proposed as a new superconducting qubit. We describe a simple method to create a double-well potential for an individual fluxon trapped in a long elliptic annular Josephson tunnel junction characterized by an intrinsic non-uniform width. The distance between the potential wells and the height of the inter-well potential barrier are controlled by the strength of an in-plane magnetic field. The manipulation of the vortex states can be achieved by applying a proper current ramp across the junction. The read-out of the state is accomplished by measuring the vortex depinning current in a small magnetic field. An accurate one-dimensional sine-Gordon model for this strongly non-linear system is presented, from which we calculate the position-dependent fluxon rest-mass, its Hamiltonian density and the corresponding trajectories in the phase space. We examine the dependence of the potential properties on the annulus eccentricity and its electrical parameters and address the requirements for observing quantum-mechanical effects, as discrete energy levels and tunneling, in this two-state system.