Dissertation/Thesis Abstract

Utilizing Brillouin Interactions for Optical Control of Bulk Acoustic Waves
by Kharel, Prashanta, Ph.D., Yale University, 2019, 248; 13885352
Abstract (Summary)

Acoustic-wave devices have become indispensable components of modern technologies with applications ranging from time-keeping to signal processing. Since acoustic waves can store information for extended periods of time in compact mode volumes and mediate interactions between different types of excitations (photons, microwaves, and defect centers), phonons are intriguing resources for emerging quantum technologies.

In order to efficiently utilize mechanical degrees of freedom for both scientific and technological applications ranging from studies of decoherence to precision metrology and quantum information, we seek long-lived phonons that are less sensitive to thermal noise. Often times, this means achieving coherent control of high-frequency mechanical modes that are more decoupled from their thermal environment or operations at cryogenic temperatures.

In this context, bulk acoustic wave (BAW) resonators are crucial resources for both classical and quantum technologies. Since acoustic dissipation within crystalline solids plummets at cryogenic temperatures, BAW resonators, which are formed by shaping the surfaces of pristine crystals, can support long-lived phonon modes. To date, electromechanical coupling has been used to access such long-lived phonons within piezoelectric crystals, enabling various scientific and technological applications ranging from tests of Lorentz symmetry to low-noise oscillators. However, if we could access such bulk acoustic phonons with light, we have an opportunity to access high-frequency phonons in practically any transparent crystal, opening new avenues for sensitive metrology, materials spectroscopy, high-performance lasers, and quantum information processing.

In this thesis, we demonstrate the optical control of long-lived, high-frequency phonons within BAW resonators. We utilize Brillouin interactions to engineer tailorable coupling between free-space laser beams and high Q-factor phonon modes supported by a plano-convex BAW 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.

For efficient optical control of bulk acoustic phonons, we utilize resonant multimode interactions by placing the bulk crystal inside an optical cavity. Resonant interactions permit us to dramatically enhance the optomechanical coupling strength. Utilizing enhanced optomechanical interactions in a system where we can select between Stokes and the anti-Stokes process, we demonstrate cooling and parametric amplification of bulk acoustic modes as a basis for ultra-low-noise oscillators and high-power lasers.

Finally, we enhance the optomechanical coupling strength to be larger than the optical and mechanical decoherence rates, creating hybridized modes that are part light and part sound. Deterministic control of long-lived bulk acoustic phonons with light in this so-called strong coupling regime opens the door to applications ranging from quantum transduction to quantum memories.

Indexing (document details)
Advisor: Rakich, Peter T
Commitee: Harris, Jack GE, Schoelkopf, Robert J, Girvin, Steven M, Zadok, Avinoam
School: Yale University
Department: Physics
School Location: United States -- Connecticut
Source: DAI-B 81/9(E), Dissertation Abstracts International
Subjects: Physics, Optics, Acoustics
Keywords: Acoustics, Brillouin scattering, Nonlinear optics, Optomechanics, Quantum information
Publication Number: 13885352
ISBN: 9781658491969
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