Cavity optomechanics studies the interaction between mechanical resonators and optical cavities through radiation pressure forces and aims to harness this interaction for applications in the areas of high precision metrology, tests of fundamental quantum mechanics, or quantum information processing. For the most ambitious of these applications it is necessary that the mechanical resonator has a sufficiently high mechanical quality factor such that it can undergo at least a few coherent oscillations before interacting with incoherent thermal phonons. Furthermore, the optomechanical coupling must be large enough to make the interaction between optics and mechanics probable and, ideally, deterministic. This work pursues both goals using a thin membrane in the middle (MIM) of an optical cavity. This is a common configuration in cavity optomechanics but most experiments to date have lowmechanical quality factors and optomechanical couplings.@en

We fabricate photonic crystal SiN membranes with reflectivity > 99.9% at 1550 nm. These form a platform for studying arrays of mechanical oscillators inside optical cavities, which can potentially reach strong single-photon optomechanical coupling.@en

All quantum optomechanics experiments to date operate at cryogenic temperatures, imposing severe technical challenges and fundamental constraints. Here, we present a novel design of on-chip mechanical resonators which exhibit fundamental modes with frequencies f and mechanical quality factors Qm sufficient to enter the optomechanical quantum regime at room temperature. We overcome previous limitations by designing ultrathin, high-stress silicon nitride (Si3N4) membranes, with tensile stress in the resonators’ clamps close to the ultimate yield strength of the material. By patterning a photonic crystal on the SiN membranes, we observe reflectivities greater than 99%. These on-chip resonators have remarkably low mechanical dissipation, with Qm∼108, while at the same time exhibiting large reflectivities. This makes them a unique platform for experiments towards the observation of massive quantum behavior at room temperature.@en