Fabrication methods for high-coherence and scalable fluxonium qubits

A practical superconducting quantum computer requires a large number of physical qubits with high operation fidelity. The fluxonium qubit, where a Josephson junction is shunted by a super-inductor made of a junction array, can achieve both long coherence time and high gate speed, which ultimately leads to high-fidelity operations. However, wafer-scale fabrication is challenging as the current Josephson junction fabrication techniques rely heavily on the precise control of resist thicknesses and evaporation angles. Here, we report a junction fabrication method to achieve wafer-scale junction array fabrication with a Manhattan-style design. Such a junction design has a limited dependence on process variations and precise parameter control at wafer-scale. At the same time, through integrating high-quality materials like TiN and Tantalum, increased coherence times are observed, which paves the way for high-fidelity multiple-qubit processors based on fluxonium.