Doctor of Philosophy (PhD)
In 1916, Albert Einstein predicted the existence of gravitational waves based on his new theory of general relativity. He predicted an accelerating mass with a non-zero quadrupole moment would emit energy in the form of gravitational waves. Often referred to as ripples in space-time, gravitational waves are extremely small by the time reach Earth, potentially having traveled hundreds of megaparsecs. It is common for these ripples in space-time to stretch and squeeze matter 1000 times smaller than the width of a proton.
Laser interferometer observatories were first built in the 1990s in the US and Europe, and as sensitivity improvements were made, the chance of making the first direct observation with a ground-based interferometer improved. Eventually, the Advanced Laser Interferometer Gravitational Wave Observatory (aLIGO) became sensitive to gravitational waves and the first detection was made on September 14th, 2015 (GW150914). This date marks the beginning of the gravitational wave astronomy era. Since this discovery, LIGO and Virgo have completed three observing runs and over 90 detections not just from binary black holes (BBH), but binary neutron stars (BNS) and black hole neutron star mergers (BHNS). The rate at which detections are made in the ground based gravitational wave detector network has increased as sensitivity improvements are made in the detectors. One limiting noise source in these detectors is quantum noise. Quantum noise is made up of radiation pressure noise and shot noise. This dissertation focuses on several experiments centered around improving the quantum noise in the next generation of gravitational wave detectors. Chapter one provides general background knowledge of gravitational waves. It reviews the minor derivations required to produce gravitational waves according to general relativity, as well as astrophysical sources that produce these waves. Additionally, noise sources, primarily quantum, and the standard quantum limit (SQL) are examined. Chapter two details the workings of an optical spring. The ensuing chapters review experiments conducted in the quantum optics lab. Chapter three discusses the room temperature optomechanical squeezed light experiment and the corresponding subtraction technique analysis. Chapter four examines concepts for a double optical spring. Chapter five outlines the process of achieving power stabilization of a laser, passively, without the use of any feedback. Chapter six discusses the main work of this thesis, a displacement measurement of a Fabry-Perot cavity that beats the SQL. And finally, Chapter seven outlines future experiments that could be implemented, given our current experimental set up.
Cullen, Torrey, "Surpassing the Standard Quantum Limit using an Optical Spring" (2022). LSU Doctoral Dissertations. 5925.