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Title: Towards surpassing the standard quantum limit using optical springs
Author: Macarthur, John
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2014
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The existence of Gravitational waves is a prediction that arose from Einstein's theory of general relativity. So far their direct detection has eluded scientists with Einstein himself believing they would never be detected. However, recent developments in advanced interferometric detectors should allow the first detections to be made when they are commissioned later this decade. This will open up an entire new field of astronomy giving deeper understanding to the physics of and proving Einstein's general theory of relativity. Astronomers always want bigger telescopes whether it is to see further or to see more detail and this will no doubt occur with gravitational wave telescopes. Hence, further improvements in sensitivity will be required. This thesis examines techniques for improving sensitivity beyond the standard quantum limit, a future limit to sensitivity, using optical rigidity. By coupling two suspended cavity mirrors together using only the light circulating between them the response of the system changes such that a linear restoring force is created on both cavity optics, the "optical spring". The first experiment carried out in the scope of this thesis shows how an intentionally applied signal that changes the position of the input mirror in a rigidly coupled cavity is transferred via the optical spring to a position change of the output cavity mirror. A small independent interferometer, a so-called local readout, is used to monitor the displacement of the output cavity mirror allowing the position of the input mirror to be inferred. This experiment verifies that it is possible to gather information on the position of the input mirror via the local readout interferometer the photons of which have never interacted with the input mirror. The local readout device was able to measure a coupled motion between the cavity mirrors, via the optical spring, of 10⁻¹³m at 922 Hz. Hence this experiment can be considered as the first demonstration of an optical bar configuration which has been previously shown to be a type of quantum non-demolition measurement. In the second experiment an optical spring, present in a 10m cavity used as a frequency reference, provides a peak in the optical gain of this cavity. The peak in gain, due to the resonance of the optical spring, is then shown to enhance the frequency stability of the 10m cavity around the optical spring frequency. An increase in sensitivity of 3 dB across a 50 Hz window centred around 200 Hz was measured showing that this is a good example of how the optical spring can also be used to improve high-precision classical measurements. Overall this thesis provides examples of how optical springs can be used as a building block for improvements of high precision interferometry and quantum measurement. These technologies are likely to play a key role in future gravitational wave detectors such as the Einstein Telescope.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics