Serpico, Giuseppe (2024) Harnessing Superconducting Microwave Circuits for Material Studies and Advanced Qubit Architectures. [Tesi di dottorato]

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Abstract

This thesis investigates the design, fabrication, and application of superconducting resonators for material studies and the development of advanced qubit architectures in quantum computing. Superconducting resonators play a crucial role in probing quantum materials and serve as essential components in various quantum technologies, including qubits for quantum computing. The study of superconducting resonators is linked to the study of high-temperature superconductors, such as cuprates like BSCCO, and the Josephson effect, both of which are critical to the functionality of superconducting qubits and devices. A key focus of this work is the design and characterization of high-quality factor superconducting resonators, which are employed as read-out circuits to explore the fundamental properties of exotic materials, including high-temperature superconductors, and novel Josephson junctions. These ferromagnetic-based junctions hold great promise for advanced quantum computational circuits. In particular, ferromagnetic junctions exhibit tunable F-layer properties, making them potential candidates for memory devices and contributing to the development of the innovative Ferro-Transmon qubit. In this thesis, I simulated and optimized the design parameters for the Ferro-Transmon qubit, proposing novel solutions for applying the required in-plane magnetic field to tune the junction's properties. Another central aspect of this research focuses on high critical temperature BSCCO flakes, a superconducting van der Waals (vdW) material used to create Josephson junctions. By twisting two BSCCO flakes at a "magic angle," I created a heterostructure that behaves as a single superconducting Josephson junction, offering an unprecedented degree of tunability. This advancement opens new possibilities for qubit designs, including the "Flowermon" qubit, which is theorized to reduce quasiparticle noise through the unique properties of twisted BSCCO junctions. As part of this work, I coupled a BSCCO flake to a resonator, leading to a significant discovery regarding the behavior of vdW heterostructures under varying power and temperature conditions. Specifically, I identified non-resonant Two-Level Systems (TLS) in BSCCO, an important finding for understanding noise sources and material interactions, which are crucial for their application in quantum technologies. All samples measured in this thesis were fabricated in-house using advanced techniques, including magnetron sputtering, electron beam lithography, and reactive ion etching. Cryogenic fabrication methods for van der Waals heterostructures, such as the controlled exfoliation of 2D materials and the fabrication of twisted BSCCO Josephson junctions, are also thoroughly detailed. These experimental advances contribute to the ongoing development of scalable, noise-resistant qubit systems for future quantum technologies.

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