Mihir Khanna Dissertation Defense

Thesis Title: Cavity Electo-Optics for Quantum Transduction and Sensing Abstract: I present all-dielectric cavity electro-optic systems for efficient conversion between microwave and telecom-wavelength photons for quantum networks and for optical sensing and control of microwave fields. By spatially overlapping microwave and optical cavity modes within lithium niobate, a nonlinear optical crystal, I harness the Pockels effect to parametrically couple these disparate frequency domains. This dissertation explores how bulk dielectric resonators can provide the field confinement, low loss, and optical power handling required to perform as an electro-optic transducer with state-of-the-art efficiency at room-temperature, and comparable to cryogenic superconducting platforms. The work follows an iterative progression in which the microwave resonator geometry evolves to strengthen the electro-optic interaction without sacrificing the advantages of a bulk optical cavity. The first generation uses a centimeter-scale lithium-niobate slab that serves simultaneously as a dielectric microwave resonator and as the nonlinear medium within a Fabry--Pérot optical cavity. Its geometry is engineered to provide spatial and polarization overlap between the microwave and optical fields, while the partially dielectric-filled optical cavity enables phase matching and single-sideband operation. At room temperature, this device demonstrates coherent percent-level microwave--optical transduction under triply resonant operation, in which the microwave, optical pump, and output fields are simultaneously resonant with modes of the system. I next develop a composite resonator in which a smaller lithium niobate crystal is sandwiched between higher-permittivity titanium dioxide crystals. This architecture reduces the microwave mode volume by two orders of magnitude, substantially strengthening the electro-optic interaction while preserving the power handling and low-noise operation of the all