Optomechanics in an ultrahigh-Q slotted 2D photonic crystal cavity

Optical guided wave dielectric structures with nanoscale slots are known to provide strong electric field enhancements in the slotted region, enabling strong light-matter interactions. Here we demonstrate an ultrahigh-Q slotted 2D photonic crystal cavity for the purpose of obtaining strong interaction between the internal light field and the mechanical motion of the slotted structure. The experimentally measured optical quality factor is Q=1.2x10^6 for a cavity with a simulated effective optical modal volume of 0.04 cubic wavelengths. Optical transduction of the thermal Brownian motion of the fundamental in-plane mechanical resonance of the slotted structure (151 MHz) is performed, from which an optomechanical coupling of 140 GHz/nm is inferred for an effective motional mass of 20 pg. Dynamical back-action of the optical field on the mechanical motion, resulting in both cooling and amplication of the mechanical motion, is also demonstrated.