Pushing the Boundaries of Impedance and Nonlinearity in Superconducting Quantum Circuits Based on Granular Aluminum

Superconducting circuits based on high kinetic inductance materials are promising candidates for future quantum technologies, owing to their magnetic field resilience, low microwave losses, and lithographic scalability. In this thesis, we explore the properties of granular aluminum (grAl) resonators in two distinct geometries, using the nonlinear kinetic inductance of grAl for applications in superconducting quantum circuits. In the first part, we present compact meandered ring resonators fabricated using a single-step electron-beam lithography and lift-off process. By optimizing film resistivity and geometry, we achieve superinductors with characteristic impedances exceeding \(100~\mathrm{k}\Omega\), corresponding to total inductances of several microhenries, while maintaining internal quality factors on the order of \(10^{5}\) in the single-photon regime. In the second part, we investigate DC-tunable resonators based on a \(3\lambda/4\) fractal geometry that allows direct current injection for in-situ tuning of the resonance frequency. We achieve frequency tunability up to \(4.5\%\) and analyze the nonlinear kinetic inductance using models based on Ginzburg-Landau, Mattis-Bardeen-BCS, and an effective Josephson-junction-array model. ... mehrThis work establishes granular aluminum as a material for realizing high-impedance and frequency-tunable superconducting circuits, offering new opportunities for advanced applications in protected qubits, hybrid quantum systems, broadband phase shifters, and three-wave mixing parametric amplifiers.