Spectroscopy of fractional Josephson vortex molecules

Using tiny current injectors we create κ discontinuities of the Josephson phase in a long Josephson junction. The junction reacts at the discontinuities by creating fractional Josephson vortices of size λJ pinned at them. Such vortices carry the flux Φ, which is a fraction of the magnetic flux quantum Φ0∼2.07 x 10-15 Wb. Being pinned, a fractional vortex has an eigenfrequency (localized mode), which depends on κ and applied bias current, and which lays within the plasma gap. If one considers a molecule consisting of several coupled fractional vortices, the eigenfrequency will split into several modes. We report on spectroscopy of a fractional vortex molecule performed in the thermal regime.