Fabrication of Fluxonium Qubit on Al and Al2O3/Ta based Superconducting Microwave Circuit

Fluxonium superconducting qubits have demonstrated high coherence times and exceptional gate fidelity, making them promising candidates for quantum information applications. To develop multi-fluxonium qubit systems on quantum chips, it is crucial to integrate high-quality superconducting microwave circuits with fluxonium qubits. In this study, we fabricate and compare two distinct types of Al/AlOx/Al-based fluxonium qubits, utilizing either Al2O3-capped tantalum (Ta) or aluminum (Al) superconducting microwave circuits. Our fabrication process begins with a UHV-sputtered Ta film, complemented by an in situ Al2O3 capping layer, or an e-beam evaporated Al film, all deposited on a-plane sapphire substrates. We utilize photolithography and dry etching techniques to pattern microwave transmission lines, readout resonators, and antenna pads for the fluxonium qubits. Subsequently, we fabricate Al/AlOx/Al Josephson junctions and junction arrays using e-beam lithography. The resulting coplanar waveguide (CPW) resonators demonstrate a quality factor above Qi=3×10^5 in the low photon limit, highlighting the high quality of the materials and the fabrication process.