The interaction between light and mechanical motion has been harnessed for a variety of scientific and technological applications ranging from studies of decoherence to precision metrology and quantum information. Central to these goals of optomechanics, and more generally of quantum information science, is harnessing long-lived phonons while minimizing thermal noise. Often time, this means achieving coherent control of high-frequency mechanical modes. Acoustic modes having high Q-factors and high frequencies are less sensitive to thermal noise as they are more decoupled from their thermal environment.
In this context, macroscale systems based on bulk acoustic wave (BAW) resonators are intriguing resources for optomechanics. Since acoustic dissipation within pristine crystalline solids plummets at cryogenic temperatures, BAW formed by shaping surfaces of pristine crystals can support long-lived phonons within macroscopic device geometries. So far, electromechanical coupling has been used to access such high Q-factor (8 billion) phonon modes at relatively low frequencies (5-200 MHz). However, if we could access these phonons with light, we have an opportunity to achieve such impressive performance at much higher frequencies (10-100 GHz), opening new avenues for sensitive metrology, materials spectroscopy, high-performance lasers, and quantum information processing.
In this thesis, we demonstrate optical control of long-lived, high-frequency phonons within BAW resonators. Utilizing Brillouin interactions, we engineer tailorable coupling between laser light and high Q-factor phonon modes supported by a plano-convex bulk acoustic resonator. Analogous to the Gaussian beam resonator design for optics, we present analytical guidelines, numerical simulations, and novel microfabrication techniques to create stable acoustic cavities that support long-lived bulk acoustic phonons. By placing these high-performance bulk acoustic resonators inside an optical cavity, we present a novel device strategy to translate cryogenic Brillouin physics into high-frequency cavity optomechanical systems for applications ranging from high-power lasers and low-noise oscillators to quantum transducers and quantum memories.
Host: Jack Harris
jack.harris@yale.edu