Dissertation Defense: Prashanta Kharel, Yale University, “Utilizing Brillouin Interactions for Optical Control of Bulk Acoustic Waves”

Event time: 
Monday, April 15, 2019 - 9:00am to 10:00am
17 Hillhouse Avenue (HLH17), Yale Quantum Institute - Seminar Room See map
17 Hillhouse Avenue
New Haven, CT 06511
Event description: 

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; mechanical 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 resource 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 such phonons with light, we have an opportunity to push such world-record performance to 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 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 application ranging from high-power lasers and low-noise oscillators to quantum transducers and quantum memories.

Thesis Advisor: Peter Rakich