Towards Novel Tunability Schemes for Hybrid Ferromagnetic Transmon Qubits

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.