Brillouin optomechanics in whispering-gallery-mode resonators: towards cryogenic operation and non-Gaussian state manipulation using phonon addition and subtraction

Abstract

The objective of this thesis is to explore the potential of Brillouin scattering in whispering-gallery- mode micro-resonators for quantum optomechanics applications. The mechanical state of a sound-wave around the circumference of the resonator is transduced into an optical field. With heterodyne detection, the phase-space distribution of the acoustic mode is measured, and an s-parametrized Wigner function with s = −219 is obtained, which advances the state-of-the-art for optics based measurements. Using photon detectors in tandem with this state read-out allows for heralded measurements at the time of a single-phonon addition or subtraction operation. The transduced optical state showed a strong perturbation, doubling or tripling the quadrature variance upon single or double phonon subtraction, respectively. The Gaussian phase- space profile redistributes into a ring shape, which was resolved using the precision of the phase- space measurement, able to resolve features down to σ = 9.4 in units of the zero-point fluctuation. Moreover, a pump-probe measurement technique was developed, and first results show signs of mechanical substructures on an optical resonance (optomechanically induced transparency), when the optomechanical interaction strength is enhanced sufficiently by the pump laser intensity. This work provides a useful foundation for further studies in both applied and fundamental physics using Brillouin scattering. To experimentally achieve these results, a technique to attain a continuous spectrum with a thermally tuned laser was developed, vastly simplifying the identification of a set of one mechanical and two optical modes that have significant optomechanical interaction. Advances were made in the thermometry for this type of resonator, with a method to use temperature-dependent spectral shifts to understand the thermal bath right in the volume of material that is optomechanically active. Furthermore, achievements around the experimental platform are presented, ranging from the pulling of tapered, vacuum-compatible fibers, to the fabrication and handling of resonators for stable and reliable optics experiments.