Quantum coherence of Josephson vortices in high impedance long junctions

The physics of Josephson vortices in long junctions spans from nonlinear soliton dynamics with relativistic effects to the interesting applications of coherent microwave generation. In these experiments, however, the vortices were described as classical particles. This non-quantum behavior mainly stems from geometrical properties of the long junction, in particular the inductance of the electrodes.

With the advent of high kinetic inductance circuits, relaxed constrains for quantum Josephson vortices are at reach.

In our experiment we propose a coupled long Josephson junction-resonator system and determine the quantum states of various inherent vortex configurations with a dispersive readout scheme. The experimentally observed energy spectrum is compared with theoretical predictions of a single coherently tunneling vortex. We find signatures of a quantum two-level system and present measured coherence and relaxation times.