Radiation linewidth of a long Josephson junction in the flux-flow regime

TL;DR

This paper presents a theoretical model for the radiation linewidth in long Josephson junctions in the flux-flow regime, highlighting how fluxon density affects linewidth and internal fluxon dynamics.

Contribution

It introduces a collective coordinate approach based on the perturbed sine-Gordon model to calculate radiation linewidth considering internal fluxon degrees of freedom.

Findings

Linewidth is larger at low fluxon density.

Linewidth decreases as fluxon density increases.

A crossover from broad to narrow linewidth is predicted with increasing fluxon density.

Abstract

Theoretical model for the radiation linewidth in a multi-fluxon state of a long Josephson junction is presented. Starting from the perturbed sine-Gordon model with the temperature dependent noise term, we develop a collective coordinate approach which allows to calculate the finite radiation linewidth due to excitation of the internal degrees of freedom in the moving fluxon chain. At low fluxon density, the radiation linewidth is expected to be substantially larger than that of a lumped Josephson oscillator. With increasing the fluxon density, a crossover to a much smaller linewidth corresponding to the lumped oscillator limit is predicted.