  Experiments towards realizing a readout of superconducting qubits by using
ballistic Josephson vortices are reported. We measured the microwave radiation
induced by a fluxon moving in an annular Josephson junction. By coupling a flux
qubit as a current dipole to the annular junction, we detect periodic
variations of the fluxon's oscillation frequency versus magnetic flux through
the qubit. We found that the scattering of a fluxon on a current dipole can
lead to the acceleration of a fluxon regardless of a dipole polarity. We use
the perturbation theory and numerical simulations of the perturbed sine-Gordon
equation to analyze our results.
