Interferometric Precision Measurement with Macroscopic Silicon Optomechanics

Citation

Markowitz, Aaron Gregory (2024) Interferometric Precision Measurement with Macroscopic Silicon Optomechanics. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/wnm8-nb48. https://resolver.caltech.edu/CaltechTHESIS:06022024-152003367

Abstract

Optomechanical sensors provide our most sensitive measurements of spacetime, including observations of gravitational waves by laser interferometric detectors. However, even state of the art detectors like the Advanced Laser Interferometric Gravitational-Wave Observatory (LIGO) are still tens of orders of magnitude away from the measurement limits imposed by Heisenberg uncertainty. This thesis maps out the contours of mechanical and optical losses limiting next generation gravitational wave interferometers, and describes several experiments and analyses to improve those limitations. We review the theory of optomechanical force sensing to understand the influence of optical radiation pressure on the dynamics of mechanical oscillators. We analyze several modified Mach-Zehnder interferometers and show how radiation pressure can be a resource for quantum measurement, including by establishing a surprising optical spring effect in a cavity held on-resonance. The most developed proposal is for a phase-sensitive optomechanical amplifier to avoid the photodetection losses that may limit next-generation gravitational wave interferometers utilizing cryogenic silicon mirrors and ≈2000 nm infrared lasers. The amplifier calls for high quality mechanical oscillators made of single crystal silicon, which we fabricate. We describe our efforts to develop a testbed for cryogenic mechanical loss measurements of silicon oscillators and thin film coatings. And, we show how Bayesian inference can be used to improve our understanding of the physical mechanisms limiting a system’s mechanical loss. Finally, we describe the optical, mechanical, and electronic design of a prototype phase sensitive optomechanical amplifier. The prototype is useful for testing the control system required to implement the full amplifier, and we characterize the current control scheme and the scheme for near-term upgrades. Our latest measurements show a clear path to steadily improving the amplifier’s noise figure with well understood technology.

Thesis Files