A hybrid ferromagnetic transmon qubit: circuit design, feasibility and detection protocols for magnetic fluctuations

TL;DR

This paper proposes a hybrid superconducting qubit using ferromagnetic Josephson junctions, enabling digital frequency tuning via magnetic fields, and explores its potential for magnetic fluctuation detection and studying magnetism-superconductivity interactions.

Contribution

It introduces a novel hybrid ferromagnetic transmon qubit design utilizing hysteretic ferromagnetic barriers for digital frequency control and discusses its application in magnetic noise detection.

Findings

Hysteretic ferromagnetic barriers enable digital qubit tuning.

The qubit can detect magnetic fluctuations.

Potential to study magnetism and superconductivity interplay.

Abstract

We propose to exploit currently available tunnel ferromagnetic Josephson junctions to realize a hybrid superconducting qubit. We show that the characteristic hysteretic behavior of the ferromagnetic barrier provides an alternative and intrinsically digital tuning of the qubit frequency by means of magnetic field pulses. To illustrate functionalities and limitation of the device, we discuss the coupling to a read-out resonator and the effect of magnetic fluctuations. The possibility to use the qubit as a noise detector and its relevance to investigate the subtle interplay of magnetism and superconductivity is envisaged.