Optomechanical enhancements for applications in metrology

Abstract

The reciprocal interaction between light and matter has been attracting increasing interest in recent years thanks to the developments in the field of optomechanics. A typical optomechanical system can be exposed to the radiation pressure force thanks to the amplifying action of an optical cavity, which can increase the level of the interaction by several orders of magnitude. The extraordinary interplay between the light and the mechanical components of the cavity grants access to remarkably delicate applications, which include the cooling of an oscillator to its motional ground state, the generation of non-classical optical states, and refined quantum optical measurements.

A particular indicator of the capabilities of an optomechanical system is its mechanical quality factor, which gives a measure of the coherence time of the oscillator. High-quality oscillators are less susceptible to the interaction with the environment, thanks to the lower dissipation and reduced coupling of external noise. Thus, an optomechanical system with a very high quality factor enables more advanced operations. Levitated objects are particularly suitable for this, since their motional degrees of freedom are completely decoupled from any external reservoir. The levitation scheme introduced in this thesis takes the concept to extremes by considering fully coherent optical levitation of a cavity mirror. Such system would allow exceptionally pure tracking of the oscillator's position, which can be converted for example into accurate measurements of relative changes in the gravitational field.

Other approaches focusing on the improvement of the sensitivity in existing systems are also considered. Taking advantage of the incredible diversity of optomechanical structures, we show how enhanced signals can be extracted in systems as small as a nanowire or as big as an interferometer stretching over several kilometres. Each strategy is presented in relation to a specific application, while keeping the opportunity of generalizing to systems operating under very different conditions open.

Overall, the experimental and theoretical investigations presented in this thesis show that optomechanics is a valuable resource for the attainment of high-precision measurements of displacements, forces, accelerations, and other relevant physical quantities. Show more