Degree

Doctor of Philosophy (PhD)

Department

Department of Physics & Astronomy

Document Type

Dissertation

Abstract

Gravitational waves were first predicted by Albert Einstein in 1916. Calculations in the 1970s by Rainer Weiss showed an interferometer of sufficient size could realistically detect gravitational waves, which led to a grant by the National Science Foundation (NSF). With steady progress and over decades of funding by the NSF, the construction of two full scale 4km interferometers was approved and began construction in 1994. This project, coined LIGO the Laser Interferometer Gravitational-wave Observatory, came to be a worldwide collaboration of scientists dedicated to the discovery and study of gravitational waves. In 2015, both LIGO detectors detected a coincident inspiral waveform of two black holes originating 1.3 billion light years away, ushering in the era of gravitational wave astronomy. To maximize the number of gravitational wave detections, we desire the lowest noise in the frequency band which we would expect gravitational waves to appear. Two quantum effects increase the noise for LIGO, shot noise at high frequency and radiation pressure at low frequencies. The experiments throughout this dissertation seek to understand and mitigate this quantum noise within ground-based gravitational wave observatories such as LIGO.

As ground based detectors approach the standard quantum limit, it has become important to investigate techniques to reduce the total noise beyond this limit. Through the optical spring effect, these results demonstrate an interferometric configuration which has been shown to reduce noise below the standard quantum limit by 2.8 dB. This configuration when dynamically tracking a gravitational wave chirp, has also been shown to increase the SNR by up to a factor of 40. This work is presented alongside a passive power stabilization technique, demonstrating a maximum power suppression by a factor of 125. This technique provides a proof of principle how the laser power can be stabilized without the need for a pick-off and active feedback suppression, which may be useful for next generation detectors with higher input powers. Finally, evidence our system should be able to push the upper mass limit of measured macroscopic quantum effects is presented. This is shown though a phonon occupation measurement of 5.2 ± 0.3 in a nano-gram micro-resonator.

Date

3-31-2025

Committee Chair

Corbitt, Thomas

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