Design, fabrication and characterization of ultrathin superconducting Aluminum lumped element resonators for spin ensemble quantum memories application

The realization of a fault-tolerant quantum computer remains one of the most significant challenges in modern physics and computer science. The physical qubits used in the Quantum Processing Units (QPUs) should be at the same time strongly coupled to controls while being well isolated from environmental noise. Hybrid systems, combining different quantum technologies, represent a promising approach to overcome the limitations of individual platforms. By performing different tasks on the most suitable physical systems, hybrid architectures can enhance the overall performance of quantum devices, with applications ranging from quantum computing to communication. In this thesis, we explore the potential of superconducting circuits as a versatile platform to implement spin ensemble quantum memories. These devices show the potential to be used to store quantum information for long times, while being easily integrated with superconducting qubits and resonators. This work is mainly focused on superconducting lumped element resonators: their design with methodologies for a more efficient development process, the fabrication procedure performed in the PiQueT cleanroom, and characterization methodologies inside a dilution refrigerator. Moreover, the use of ultrathin Aluminum films is investigated as a high critical field superconductor, as an alternative to Niobium-based alloys. Results on simulation success, two-level systems (TLS) loss mechanisms and kinetic inductance impact are reported, and performance of the Aluminum devices are compared to their copies in Niobium. With further spin resonance experiments, device compatibility with Aluminum-based qubit platforms can be assessed and the development cycle of a fully operational quantum memory can be closed.