Towards implementation of quantum noise reduction schemes in 3rd generation gravitational wave detectors

Jones, Philip ORCID: 0000-0001-7923-1415 (2022). Towards implementation of quantum noise reduction schemes in 3rd generation gravitational wave detectors. University of Birmingham. Ph.D.

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Abstract

Since the initial detection of gravitational waves in 2015, a slow and steady stream of events has been recorded. The next step is to detect more and weaker sources, probing deeper into the universe. In order to do so, our interferometers must be pushed to even greater extremes, to suppress the noise that would otherwise obscure such faint signals.

Quantum noise is perhaps the most fundamental source of noise in a laser interferometer. Arising from the inherent uncertainty in the amplitude and phase of any light source, it limits the sensitivity of all current and proposed future interferometers, especially at higher signal frequencies. The second generation detectors currently in use, such as Advanced LIGO and Virgo, are operating around the standard quantum limit---the maximum sensitivity that can be reached by employing classical techniques. For future upgrades and new detectors, advanced quantum techniques must be employed to further increase sensitivity. Advanced LIGO has already demonstrated its ability to surpass the standard quantum limit over a small range of frequencies by making use of squeezed states of light, and future improvements will increase the magnitude and frequency range of this sensitivity enhancement.

In this thesis, I will detail my work on these quantum techniques, aimed particularly at the upcoming third generation of gravitational wave detectors. This covers a wide variety of topics: different arrangements of filter cavities for improved squeezing, an alternate detection scheme that reduces both quantum and more technical noises, a mechanism that operates via complex optomechanical interactions, and more. In each of these subjects, my role has largely been to perform validation of new ideas and techniques, and to investigate the effects of varying detector parameters on the proposed scheme. To this end, I have made extensive use of a numerical frequency domain interferometer simulation tool known as finesse.

Widely used throughout the interferometer community, finesse allows the fast and accurate modelling of optical layouts. Certain advanced techniques, however, were beyond finesse's capabilities when I started my work. This thesis therefore also describes my contributions towards a full rewrite of this tool, called finesse 3. I performed a complete reimplementation of the quantum noise calculations in finesse 3, and added features necessary to model new and exciting ideas. I will explain the mathematics that finesse 3 uses to simulate interferometers, before finally giving a broader overview of its design, usage, and the great potential it has to allow investigation of ever more complex techniques for the foreseeable future.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):