Observation of Brillouin optomechanical strong coupling with an 11 GHz mechanical mode

TL;DR

This paper reports the first observation of strong optomechanical coupling at 11 GHz in a fused-silica resonator, demonstrating high coupling rates and paving the way for quantum control using light and sound.

Contribution

It demonstrates strong Brillouin optomechanical coupling at GHz frequencies in fused silica, overcoming previous material limitations and enabling quantum optomechanics applications.

Findings

Observation of normal-mode splitting indicating strong coupling

Achieved coupling rate of 39 MHz surpassing decay rates

Utilized auxiliary pump resonance to enhance coupling

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.