Dynamics of an annular Josephson junction in a rotating magnetic field

We study analytically and numerically the dynamics of a solitary fluxon in a long annular damped Josephson junction placed into a rotating magnetic field, which is produced by superposition of two mutually perpendicular ac fields with a phase difference of π/2. We demonstrate that the rotating magnetic field drives the fluxon as a traveling wave. The step in the I-V characteristic, corresponding to the velocity of the fluxon coinciding with the phase velocity of the driving wave, is predicted and its size is calculated. It is also demonstrated that the I-V curve has a parabolic profile near the edges of the step. For the case where the fluxon is slowly dragged by a fast traveling wave, the drift velocity is found. The analytical results are in very good agreement with numerical experiments performed on the perturbed sine-Gordon system. Finally the system is analyzed analytically for moderate or small lengths of junctions.