Opto-acoustic Coupling in a Pristine Crystal via Brillouin Scattering

In this thesis, coupling between optics and acoustics in an optomechanical cavity is reported. The coupling is established via Brillouin scattering of light at telecom wavelengths (1550 nm) scattered from high frequency bulk acoustic waves (∼ 12 GHz) in crystalline quartz. Two optomechanical cavities are presented; one for operation at room temperature, the other for operation at milli-Kelvin temperatures. Further, simulations of the advantageous asymmetric mode spacing of the cavities and the physical criteria for the constructions are carried out. At room temperature, Brillouin lasing is obtained with a lasing threshold of 15 mW. Furthermore, strong coupling between the hybridised optical and acoustic modes is demonstrated at different input powers, allowing for the estimation of a single photon coupling rate of g0/2π ≃ (1.2 ± 0.2) Hz. The strong coupling demonstrated at room temperature in this work is an important milestone building towards achieving strong coupling at milli-Kelvin temperatures. The latter is of huge interest as it will allow for quantum coherent state transfer which in turn will open the door to interrogating alternative theories of physics e.g., quantum phenomena in macroscopic objects, and hybrid quantum technologies, such as quantum memories and quantum transducers. Therefore working towards this direction, finally, the design of a state-of-the-art cavity for ground state operation as well as its characterisation is presented.