Cavity optomechanics with ultra-high Q crystalline micro-resonators

TL;DR

This paper reports the first observation of optomechanical coupling in ultra-high Q crystalline whispering-gallery-mode resonators, demonstrating their potential for advanced quantum and optomechanical applications.

Contribution

It introduces ultra-high Q crystalline micro-resonators with record optical and mechanical qualities, enabling new regimes of optomechanical phenomena and measurements.

Findings

Optical quality factors >10^{10} achieved

Mechanical Q factors >10^{5} observed

Mechanical modes up to 20 MHz with high sideband factors

Abstract

We present the first observation of optomechanical coupling in ultra-high Q crystalline whispering-gallery-mode (WGM) resonators. The high purity of the crystalline material enables optical quality factors in excess of 10^{10} and finesse exceeding 10^{6}. Simultaneously, mechanical quality factors greater than 10^{5} are obtained, still limited by clamping losses. Compared to previously demonstrated cylindrical resonators, the effective mass of the mechanical modes can be dramatically reduced by the fabrication of CaF2 microdisc resonators. Optical displacement monitoring at the 10^{-18} m/sqrt{Hz}-level reveals mechanical radial modes at frequencies up to 20 MHz, corresponding to unprecedented sideband factors (>100). Together with the weak intrinsic mechanical damping in crystalline materials, such high sindeband factors render crystalline WGM micro-resonators promising for backaction evading measurements, resolved sideband cooling or optomechanical normal mode splitting. Moreover, these resonators can operate in a regime where optomechanical Brillouin lasing can become accessible.