Annular Long Josephson Junctions in a Magnetic Field: Engineering and Probing the Fluxon Interaction Potential

The interaction of a Josephson fluxon with an external magnetic field-induced potential in a long Josephson junction is investigated experimentally. The thermal activation of the fluxon from a potential well is observed and experiments probing its predicted quantum properties are discussed. A method for engineering a magnetic double-well potential for a fluxon is proposed and the use of the coupled fluxon states for quantum computation is suggested.