Cavity optomechanical feedback cooling and magnetic eld sensing

This work is focused on the theoretical and experimental study of the interaction between electromagnetic radiation and mechanical micro-resonators. Through the radiation pressure interaction, it is possible to steer micromechanical oscillators into exotic, non-classical motional states - e.g. a Schrödinger cat state.

The main requirement to observe a non-classical behaviour of massive mechanical oscillators is the ability to cool such oscillators into their motional quantum ground state. In the first part of this work, we investigate the feedback cooling of a tethered membrane vibration mode by radiation pressure.

The presented experiment paves the way towards quantum control of macroscopic mechanical systems. Due to the resonant enhancement of both optical and mechanical response, the cavity optomechanical devices allow ultra-sensitive measurements of displacement, forces or masses. The measurement precision is ultimately limited by the classical noise sources coupled to the system, e.g. thermal noise from the environment, or probe beam shot noise.

In the second part if this work, we demonstrate that by interfacing the optomechanical sensor with a squeezed light, we can improve both its sensitivity and bandwidth. Specifically, we are using an on-chip SiO2=Si whispering-gallery-mode resonator as a room temperature magnetic eld sensor. In a proof-of-concept experiment, we show that at the frequencies, where the probe laser shot noise is the dominating noise source, injection of squeezed state lowers the detection noise oor thereby improving the peak sensitivity.

Furthermore, the squeezed light broadens the frequency range at which thermal noise dominates, which increase the overall bandwidth of the sensor.