DEPHASING LENGTH AND COHERENCE OF A QUANTUM SOLITON IN AN IDEAL LONG JOSEPHSON-JUNCTION

We study the internal dephasing of a quantum soliton (fluxon) via its interaction with thermal plasmons. We show that dephasing occurs even when the excitations of the system are completely decoupled and there is no dissipation. The dephasing length of the fluxon (below which quantum coherence is maintained) is evaluated. It is found to be much longer than the width of the fluxon when the temperature is kept below the plasmons' energy gap. Thus there is a quantum regime for the ideal Josephson junction fluxon. We comment about the experimental test of our predictions. © 1995 The American Physical Society.