Abstract
Recent significant achievements in fabricating low-loss optical and mechanical elements have aroused intensive interest in optomechanical devices which couple optical fields to mechanical oscillators, e.g., in laser interferometer gravitationalwave (GW) detectors. Not only can such devices be used as sensitive probes for weak forces and tiny displacements, but they also lead to the possibilities of investigating quantum behaviors of macroscopic mechanical oscillators, both of which are the main topics of this thesis. They can shed light on improving the sensitivity of quantum-limited measurement, and on understanding the quantumto- classical transition. This thesis is a collection of publications that I worked on together with the UWA group and the LIGO Macroscopic Quantum Mechanics (MQM) discussion group. In the first part of this thesis, we will discuss different approaches for surpassing the standard quantum limit for the displacement sensitivity of optomechanical devices, mostly in the context of GW detectors. They include: (i) Modifying the input optics. We consider filtering two frequency-independent squeezed light beams through a tuned resonant cavity to obtain an appropriate frequency dependence, which can be used to reduce the measurement noise of the GW detector over the entire detection band; (ii) Modifying the output optics. We study a time-domain variational readout scheme which measures the conserved dynamical quantity of a mechanical oscillator: the mechanical quadrature. This evades the measurement-induced back action and achieves a sensitivity limited only by the shot noise. This scheme is useful for improving the sensitivity of signal-recycled GW detectors, provided the signal-recycling cavity is detuned, and the optical spring effect is strong enough to shift the test-mass pendulum frequency from 1 Hz up to the detection band around 100 Hz; (iii) Modifying the dynamics. We explore frequency dependence in double optical springs in order to
| Original language | English |
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| Qualification | Doctor of Philosophy |
| Publication status | Unpublished - 2010 |