Progress toward optical control of mechanical geometry

We report experimental progress toward achieving strong control over the shape and effective mass of a mechanical mode [1] by optically trapping a single lattice site of a uniform phononic crystal. We expect this optically tunable defect to enable smooth localization of the spatial distribution of oscillating mass from the centimeter scale to the micron scale, enabling (among other things) qualitatively new dissipation studies, multimode Landau-Zener dynamics, and tunable optomechanical coupling to other systems on the lattice (e.g. spins or other cavities). 

Specifically, we present the fabrication of the requisite (delicate!) mechanical structures, an etching technique [2] to controllably reduce the reflectivity of Bragg mirrors without adding loss (allowing us to tune the finesse of our cavity), and the design / alignment of a vibration-isolated UHV fiber cavity system.  We present preliminary measurements showing changes in mechanical frequency consistent with our predicted change in effective mass, our attempts to directly measure effective mass, and an anomalous optomechanical damping in this system, wherein damping occurs on both the red and blue detuned sides of the optical resonance, inconsistent with the standard theory of radiation pressure or bolometrically mediated optomechanics.

 

[1] A. Z. Barasheed et al., Phys. Rev. A 93, 053811 (2016).

[2] S Bernard et al. Optics Express 28, no. 23 (2020)