Quantum Optics Seminar by Christoph Reinhardt, McGill University

Toward high single-photon cooperativity optomechanics with SiN trampoline resonators

Abstract
Mechanical resonators are ubiquitous throughout society and science, employed for force and mass detection, for optical and microwave wavelength conversion, or for fundamental studies of quantum motion. A useful tool in this context is the force exerted by light stored in an optical resonator such as a Fabry-Perot cavity. This can, among other things, be used to cool a mechanical resonator to its quantum ground state, observe quantum effects in its motion, and generate squeezed mechanical and optical degrees of freedom.

In my presentation I will talk about the fabrication and characterization of high-aspect-ratio, nanogram-scale SiN “trampoline resonators" having mechanical quality factors ~5×10^7 (mHz linewidths) and a thermally limited force noise sensitivitiy below 20 aN/Hz^(1/2) at room temperature. These devices also exhibit excellent optical properties, with no signs of optical loss from absorption or surface roughness in a finesse-20,000 optical cavity. Importantly, the demonstrated optical and mechanical performances correspond to a "single-photon cooperativity" well above 1, meaning cavity light at the level of a single photon on average will profoundly influence the trampoline's mechanical trajectory. As such, a highly stable laser lock is an absolute requirement for optomechanics experiments with this system. In the last part of the talk I will discuss our efforts to frequency-stabilize a low-power external laser to such cavities using a simple, modified Pound-Drever-Hall scheme in which a phase-modulated sideband tracks the cavity frequency.