Characterization of Quality Factors of Superconducting Resonators

Abstract

Superconducting lumped element resonators play a pivotal role in circuit quantum electrodynamics (cQED) architectures, serving both as protective filters that isolate qubits from environmental noise and as sensitive probes for qubit state readout. The performance of these resonators is fundamentally limited by various loss mechanisms that arise during device fabrication and operation. Among these, dielectric loss due to parasitic two-level systems (TLSs) residing in native oxides or dielectric layers on metal and substrate surfaces is a major source of decoherence at low powers. These losses are highly dependent on device geometry, fabrication techniques, material quality, and substrate-metal interfaces. In this project, I designed and fabricated lumped element resonators with a focus on achieving high internal quality factors (Qi). A total of four devices were fabricated using superconducting thin films and standard lithographic techniques. Each device underwent systematic optimisation of its fabrication recipe to reduce sources of loss and improve performance. Through careful design, materials selection, and fabrication process refinement, the project demonstrates pathways to enhance resonator quality and coherence, contributing to the development of more robust superconducting quantum circuits.