Energy level spectroscopy of a bound vortex-antivortex pair

Abstract

We report microwave spectroscopy of energy levels of a bound Josephson Vortex-Antivortex (VAV) state in an annular Josephson junction. The bound VAV pair is formed in the narrow long junction by applying an in-plane magnetic field. The dissociation of the bound state, which is associated with a switching of the junction from the superconducting to the resistive state, is induced by ramping up a bias current applied to the junction. This process can be mapped to the escape of a particle from a potential well. Above the crossover temperature, the pair dissociation is thermally activated, below it is induced by quantum tunnelling, which is inferred from switching current measurements. In the quantum regime, the dependence of the energy level spectrum on field and bias current is probed using microwave spectroscopy. © 2006 Springer Science+Business Media, Inc.