Scattering of SH wave by surface depression or convex in density inhomogeneous media

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Mechanical photoluminescence excitation spectra of a strongly driven spin-mechanical system

We report experimental studies of a driven spin-mechanical system, in which a nitrogen vacancy (NV) center couples to out-of-plane vibrations of a diamond cantilever through the excited-state deformation potential. Photoluminescence excitation studies show that in the unresolved sideband regime and under strong resonant mechanical driving, the excitation spectra of a NV optical transition feature two spectrally sharp peaks, corresponding to the two turning points of the oscillating cantilever. In the limit that the strain-induced frequency separation between the two peaks far exceeds the NV zero-phonon linewidth, the spectral position of the individual peak becomes sensitive to minute detuning between the mechanical resonance and the external driving force. For a fixed optical excitation frequency near the NV transition, NV fluorescence as a function of mechanical detuning features resonances with a linewidth that can be orders of magnitude smaller than the intrinsic linewidth of the mechanical mode. This enhanced sensitivity to mechanical detuning can potentially provide an effective mechanism for mechanical sensing, for example, mass sensing via measurements of induced changes in the mechanical oscillator frequency

Diamond nanomechanical resonators protected by a phononic band gap

We report the design, fabrication, and characterization of diamond cantilevers attached to a phononic square lattice. We show that the robust protection of mechanical modes by phononic band gaps leads to a three-orders-of-magnitude increase in mechanical Q-factors, with the Q-factors exceeding 10^6 at frequencies as high as 100 MHz. Temperature dependent studies indicate that the Q-factors obtained at a few K are still limited by the materials loss. The high-Q diamond nanomechanical resonators provide a promising hybrid quantum system for spin-mechanics studies