Josephson vortex coupled to a flux qubit

TL;DR

This paper demonstrates a novel method for superconducting qubit readout using ballistic Josephson vortices, showing how fluxon dynamics can be influenced by a coupled flux qubit, with experimental and theoretical analysis.

Contribution

It introduces a new approach to qubit readout utilizing fluxon scattering in Josephson junctions, combining experimental measurements with theoretical modeling.

Findings

Fluxon oscillation frequency varies periodically with magnetic flux.

Fluxon scattering can accelerate fluxons regardless of dipole polarity.

Experimental results align with perturbation theory and numerical simulations.

Abstract

Experiments towards realizing a readout of superconducting qubits by using ballistic Josephson vortices are reported. We measured the microwave radiation induced by a fluxon moving in an annular Josephson junction. By coupling a flux qubit as a current dipole to the annular junction, we detect periodic variations of the fluxon's oscillation frequency versus magnetic flux through the qubit. We found that the scattering of a fluxon on a current dipole can lead to the acceleration of a fluxon regardless of a dipole polarity. We use the perturbation theory and numerical simulations of the perturbed sine-Gordon equation to analyze our results.