RADIATION LINEWIDTH OF A LONG JOSEPHSON-JUNCTION IN THE FLUX-FLOW REGIME

Theoretical model for the radiation linewidth in a multi-fluxon state of a long Josephson junction is presented. Starting from tile perturbe d sine-Gordon model with the temperature dependent noise term, we use a collective coordinate approach in order to calculate the finite radi ation linewidth due to the internal degrees of freedom in the moving f luxon chain. At low fluxon density, the radiation linewidth is expecte d to be substantially larger than that of a lumped Josephson oscillato r. With increasing the fluxon density, a crossover to a much smaller l inewidth approaching the lumped oscillator limit is predicted.