Dissipation in mechanical resonators has a wide ranging impact in both advanced technological applications and fundamental scientific efforts. We aim to tackle mechanical dissipation on two fronts: from the optomechanical perspective, where we want to combine high mechanical Q with high optical reflectivity, we study resonators from inherently low-loss monocrystalline materials; from a more general perspective, we aim to understand and then minimize the various fundamental dissipation channels in these devices.

To simultaneously achieve high-Q and high reflectivity, we fabricate optomechanical resonators directly from an epitaxial AlGaAs Bragg reflector [1]. Compared with dielectric mirrors, the use of a single-crystal heterostructure gives rise to a significant increase in Q, while maintaining excellent reflectivity [2]. Beyond the demonstration of improved resonators for use in our cooling experiments, this work has a direct impact on ultra-high-performance interferometry applications such as gravitational wave interferometers and cavity-based optical frequency standards, where the residual phase noise, also referred to as coating thermal noise, is known to limit the overall system sensitivity.

We have recently developed an FEM-based numerical solver based on a phonon-tunneling approach [3] for the calculation of the clamping-loss-limited Q of a large class of planar mechanical resonators. In micro- and nanomechanical resonators, vibrational coupling to the substrate is a fundamental loss mechanism. In suspended devices fabricated from high quality materials, this process remains significant in vacuum and at cryogenic temperatures, and is in fact unavoidable in any non-levitating system. Combined with existing models for thermoelastic and fluidic damping, our work paves the way for CAD-based predictive design of low-loss resonators.  

[1] G. D. Cole, S. Gröblacher, K. Gugler, S. Gigan, and M. Aspelmeyer, Monocrystalline AlGaAs heterostructures for high-reflectivity high-Q micromechanical resonators in the MHz regime, Appl. Phys. Lett, 92, 261108 (2008).
[2] G. D. Cole, I. Wilson-Rae, M. R. Vanner, S. Gröblacher, J. Pohl, M. Zorn. M. Weyers, A. Peters, and M. Aspelmeyer, Megahertz monocrystalline optomechanical resonators with minimal dissipation, Proceedings of the 23rd IEEE International Conference on Microelectromechanical Systems, Hong Kong SAR, China, 24-28 January 2010.
[3] I. Wilson-Rae, Phys. Rev. B 77, 245418 (2008).