Optomechanical devices sensitively transduce and actuate motion of nanomechanical structures using light. Single--crystal diamond promises to improve the performance of optomechanical devices, while also providing opportunities to interface nanomecha
nics with diamond color center spins and related quantum technologies. Here we demonstrate dissipative waveguide--optomechanical coupling exceeding 35 GHz/nm to diamond nanobeams supporting both optical waveguide modes and mechanical resonances, and use this optomechanical coupling to measure nanobeam displacement with a sensitivity of $9.5$ fm/$sqrt{text{Hz}}$ and optical bandwidth $>150$nm. The nanobeams are fabricated from bulk optical grade single--crystal diamond using a scalable undercut etching process, and support mechanical resonances with quality factor $2.5 times 10^5$ at room temperature, and $7.2 times 10^5$ in cryogenic conditions (5K). Mechanical self--oscillations, resulting from interplay between photothermal and optomechanical effects, are observed with amplitude exceeding 200 nm for sub-$mu$W absorbed optical power, demonstrating the potential for optomechanical excitation and manipulation of diamond nanomechanical structures.
Tunable evanescent coupling is used to modify the optomechanical interactions within a split-beam photonic crystal nanocavity. An optical fiber taper probe is used to renormalize the optical nanocavity field and introduce a dissipative optomechanical
coupling channel, reconfiguring and enhancing coupling between the optical and mechanical resonances of the device. Positioning of the fiber taper allows preferential coupling to specific mechanical modes and provides a mechanism for tuning the optomechanical interaction between dissipative and dispersive coupling regimes.
We propose a scheme to realize optical quantum memories in an ensemble of nitrogen-vacancy centers in diamond that are coupled to a micro-cavity. The scheme is based on off-resonant Raman coupling, which allows one to circumvent optical inhomogeneous
broadening and store optical photons in the electronic spin coherence. This approach promises a storage time of order one second and a time-bandwidth product of order 10$^7$. We include all possible optical transitions in a 9-level configuration, numerically evaluate the efficiencies and discuss the requirements for achieving high efficiency and fidelity.
