Dissipative and Dispersive Optomechanics in a Nanocavity Torque Sensor
  Dissipative and dispersive optomechanical couplings are experimentally observed in a photonic crystal split-beam nanocavity optimized for detecting nanoscale sources of torque. Dissipative coupling of up to approximately $500$ MHz/nm and dispersive coupling of $2$ GHz/nm enable measurements of sub-pg torsional and cantilever-like mechanical resonances with a thermally-limited torque detection sensitivity of 1.2$\times 10^{-20} \text{N} \, \text{m}/\sqrt{\text{Hz}}$ in ambient conditions and 1.3$\times 10^{-21} \text{N} \, \text{m}/\sqrt{\text{Hz}}$ in low vacuum. Interference between optomechanical coupling mechanisms is observed to enhance detection sensitivity and generate a mechanical-mode-dependent optomechanical wavelength response. 
Marcelo Wu, Aaron C. Hryciw, Chris Healey, David P. Lake, Harishankar   Jayakumar, Mark R. Freeman, John P. Davis, Paul E. B...
cond-mat.mes-hall physics.optics quant-ph