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

The interaction of a Josephson fluxon with an externalmagnetic field-induced potential in a long Josephson junctionis investigated experimentally. The thermal activation of thefluxon from a potential well is observed and experimentsprobing its predicted quantum properties are discussed. Amethod for engineering a magnetic double-well potential for afluxon is proposed and the use of the coupled fluxon statesfor quantum computation is suggested.