Abstract
Achieving cavity-optomechanical strong coupling with high-frequency phonons provides a rich avenue for quantum technology development including quantum state-transfer, memory, and transduction, as well as enabling several fundamental studies of macroscopic phononic degrees-of-freedom. Reaching such coupling with GHz mechanical modes however has proved challenging, with a prominent hindrance being material- and surface-induced-optical absorption in many materials. Here, we circumvent these challenges and report the observation of optomechanical strong coupling to a high frequency (11 GHz) mechanical mode of a fused-silica whispering-gallery microresonator via the electrostrictive Brillouin interaction. Using an optical heterodyne detection scheme, the anti-Stokes light backscattered from the resonator is measured and normal-mode splitting and an avoided crossing are observed in the recorded spectra, providing unambiguous signatures of strong coupling. The optomechanical coupling rate reaches values as high as $G/2\pi = 39 \ \text{MHz}$ through the use of an auxiliary pump resonance, where the coupling dominates both the optical ($\kappa/2\pi = 3 \ \text{MHz}$) and the mechanical ($\gamma_\text{m}/2\pi = 21 \ \text{MHz}$) amplitude decay rates. Our findings provide a promising new approach for optical quantum control using light and sound.
Highlights
Since the 1920s, photon–phonon Brillouin scattering [1,2,3] has been a subject of intense and diverse study
Using an optically doubly-resonant silica micro-rod resonator, we have experimentally demonstrated Brillouin optomechanical strong coupling for high-frequency phonons (11 GHz) in the back-scattering regime
We would like to highlight that our silica system does not suffer from two-photon absorption and strong surface-induced optical losses, which currently preclude many other micro-scale devices, primarily those fabricated from silicon, from entering the strong coupling regime
Summary
Since the 1920s, photon–phonon Brillouin scattering [1,2,3] has been a subject of intense and diverse study This nonlinear optical phenomenon has been observed in numerous physical systems, including bulk crystals [4], optical fibers [5,6], integrated devices such as silicon photonic waveguides [7], silica micro-sphere resonators [8], and bulk crystalline resonators [9]. The field of Brillouin scattering is merging with the rapidly growing field of cavity quantum optomechanics. This merger offers new opportunities to control phononic degrees of freedom at the quantum level to develop new applications, such of coherent quantum state transfer between light and mechanical motion
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