Spectroscopy of superconducting charge qubits coupled by a Josephson inductance

TL;DR

This paper reports the design and experimental demonstration of inductively-coupled superconducting charge qubits using a Josephson junction as an inductance, with tunable coupling controlled by magnetic flux, confirmed by spectroscopy.

Contribution

It introduces a novel circuit design for superconducting charge qubits with flux-controlled coupling, validated through spectroscopic measurements and theoretical agreement.

Findings

Observation of anticrossings indicating qubit coupling

Coupling strength tunable via external magnetic flux

Spectroscopic results match theoretical predictions

Abstract

We have designed and experimentally implemented a circuit of inductively-coupled superconducting charge qubits, where a Josephson junction is used as an inductance, and the coupling between the qubits is controlled by an applied magnetic flux. Spectroscopic measurements on the circuit are in good agreement with theoretical calculations. We observed anticrossings which originate from the coupling between the qubit and the plasma mode of the Josephson junction. Moreover, the size of the anticrossing depends on the external magnetic flux, which demonstrates the controllability of the coupling.