Granular aluminium for fluxonium qubits

Fluxonium qubits offer a promising alternative for large-scale quantum computing by achieving lower error rates compared to conventional transmon qubits. The fluxonium qubit differs from the transmon by just one additional component: a linear inductor. To reach the fluxonium regime, it is required that the inductance provide a large inductance without adding additional capacitance or loss to the circuit. A common solution is therefore to construct the inductor using a series of hundreds of Josephson junctions. However, a large junction array adds complexity to the design and fabrication of fluxonium qubits. In this study, we circumvent the challenge of designing the optimal junction array by replacing it with a high kinetic inductance nanowire made of granular aluminium. We characterize the quality of the material by experimentally extracting the quality factors of lumped element resonators incorporating the nanowires. Subsequently, we integrate the nanowires into our fluxonium qubit design and study the impact on the fluxonium in terms of noise.