Ultracoherent Gigahertz Diamond Spin-Mechanical Lamb Wave Resonators

Phonons can mediate coupling between distant electron spins and enable a mechanical quantum network, providing an experimental platform for spin-based quantum computers. For spin mechanical systems based on defect centers in diamond, further experimental advances require ultracoherent nanomechanical resonators at a gigahertz (GHz) frequency. We report the development of an all-optical approach that excites the fundamental compression mode in a diamond Lamb wave resonator with an optical gradient force and detects the induced vibrations via strain coupling to a silicon vacancy center, specifically, via phonon sidebands in the optical excitation spectrum of the silicon vacancy. Sideband optical interferometry has also been used for the detection of in-plane mechanical vibrations, for which conventional optical interferometry is not effective. These experiments demonstrate a gigahertz fundamental compression mode with a Q factor of >10^7 at temperatures near 7 K, providing a promising platform for reaching the quantum regime of spin mechanics, especially phononic cavity quantum electrodynamics of electron spins.