Measuring and Modeling Radiation Loss in Superconducting Microwave Re-entrant Cavities

This thesis describes the potential use of re-entrant microwave resonant three-dimensional cavities as low-loss electrical component in strongly coupled electromechanical systems. In particular , I have investigated radiative processes as a loss mechanism of a re-entrant cavity in a geometry similar to those used in electromechanical experiments undertaken by the Lehnert lab. First, I present the verification of a lumped-element model describing the cavity resonance, a key electrical characteristic of a microwave re-entrant cavity, and its dependence on dimensions critical to strong electromechanical coupling. Next, I focus on modeling and measuring the total power radiating from a re-entrant cavity. To this end, I evaluated the effectiveness of surrounding the re-entrant cavity with a waveguide " choke " flange as a method of reducing total radiated power. The experimental results show the energy dissipation rate from radiation can be reduced by at least ∼ 5 × 10 4 after incorporating a radiation choke flange. This experiment aimed to inform whether a cavity with a quality factor that is limited by radiation losses is satisfactory to achieve single-photon coupling g 0 greater than κ, the electromagnetic energy dissipation rate, in an electromechanical device. The pursuit of strong single-photon electromechanical coupling is the motivation of my investigations of radiation loss in superconducting microwave re-entrant cavities. the JILA instrument shop personnel for aiding my growth as a scientist. I could not have been more fortunate to be surrounded by such a supportive, intelligent research team.