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Title: Ultra-High-Q Membrane Optomechanics with a Twist
Abstract
Recently there has been a surge of interest in the field of cavity optomechanics due to its utility in both applied and fundamental quantum optics studies. The canonical cavity optomechanical system is a Fabry-Perot (FP) cavity with a compliant end-mirror coupled to the cavity field via radiation pressure. To achieve strong optomechanical coupling—a prerequisite for achieving high sensitivity displacement measurement and efficient radiation pressure actuation—the compliant mirror must have a high-quality factor (Q), high reflectivity, and low mass. Recent innovations have led to the fabrication of mechanical resonators made from strained silicon nitride (Si3N4) thin films that demonstrate Q factors higher than 1 billion and reflectivities over 99%, utilizing the phenomenon of dissipation dilution and photonic crystal patterning. Despite rapid advancements, a single platform that meets all these unique requirements of a high-sensitivity integrated cavity optomechanical system is still an active area of research.
In this thesis defense, I will discuss how a dielectric thin film can be realized as both a high-Q nanomechanical resonator and a high-reflectivity curved mirror by combining phononic and gradient photonic crystal patterning. I will explore its application in creating a vertically integrated on-chip FP cavity. Moreover, I will address our unexpected discovery of high-Q torsional modes in strained nanoribbons and how this finding enabled us to develop a state-of-the-art chip-scale gravimeter.