Towards novel tunability schemes for hybrid ferromagnetic transmon qubits

TL;DR

This paper proposes a new type of superconducting qubit called the ferrotransmon, which uses ferromagnetic Josephson junctions for flux tuning, aiming to reduce heat dissipation and decoherence in quantum processors.

Contribution

It introduces the concept of a hybrid ferromagnetic transmon using SIsFS Josephson junctions for tunability, combining low dissipation with magnetic control.

Findings

Design and simulation of superconducting lines for magnetic control

Preliminary experimental characterization of the superconducting lines

Feasibility of on-chip magnetic tuning for ferrotransmon

Abstract

Flux tuning of qubit frequencies in superconducting quantum processors is fundamental for implementing single and multi-qubit gates in quantum algorithms. Typical architectures involve the use of DC or fast RF lines. However, these lines introduce significant heat dissipation and undesirable decoherence mechanisms, leading to a severe bottleneck for scalability. Among different solutions to overcome this issue, we propose integrating tunnel Superconductor-Insulating-thin superconducting interlayer-Ferromagnet-Superconductor Josephson junctions (SIsFS JJs) into a novel transmon qubit design, the so-called ferrotransmon. SIsFS JJs provide memory properties due to the presence of ferromagnetic barriers and preserve at the same time the low-dissipative behavior of tunnel-insulating JJs, thus promoting an alternative tuning of the qubit frequency. In this work, we discuss the fundamental steps towards the implementation of this hybrid ferromagnetic transmon. We will give a special focus on the design, simulations, and preliminary experimental characterization of superconducting lines to provide in-plane magnetic fields, fundamental for an on-chip control of the qubit frequencies in the ferrotransmon.