Observation of breathers in Josephson ladders

TL;DR

This paper reports the experimental observation of localized breather states in Josephson ladder circuits, supported by high-accuracy numerical modeling and stability analysis, advancing understanding of nonlinear localized excitations in superconducting systems.

Contribution

First direct visualization and measurement of breather states in Josephson ladders, combined with detailed numerical modeling and stability analysis.

Findings

Localized breather states observed via laser microscopy

Breather solutions match experimental I-V characteristics

Stability analysis explains persistence of excitations

Abstract

We report on the observation of spatially-localized excitations in a ladder of small Josephson junctions. The excitations are whirling states which persist under a spatially-homogeneous force due to the bias current. These states of the ladder are visualized using a low temperature scanning laser microscopy. We also compute breather solutions with high accuracy in corresponding model equations. The stability analysis of these solutions is used to interpret the measured patterns in the I-V characteristics.