Cavity-optomechanics, where photons interact with mechanical vibrations via cavity-enhanced radiation pressure, has been investigated as the platform for quantum technologies. Low-loss mechanical systems are suitable for memory applications  and their nonlinear interactions can convert optical photons to microwave photons . Introducing solid-state two-level systems in optomechanics furthermore provides new functionalities in the photon-phonon systems such as spin-dependent control of their interactions. These strain-induced interactions have been demonstrated with quantum dots and NV centers, whose energies and spins are mechanically controllable . In this talk, I show you two demonstrations about mechanical controls of GaAs excitons. One is strain-induced coupling between their dark and bright states, which enables one to optically address the long-lived dark excitons . The other is mechanical modulation of the exciton decay process, which will generate the dissipative back-action effect from excitons to the mechanical motion . Towards coherent and quantum operation, I mention the recent progress and future prospect with rare-earth materials whose decoherence is orders of magnitude smaller than those of semiconductors.
 R. Riedinger et al., Nature 556, 473 (2018).  M. Forsch et al., arXiv:1812.07588.  A. Barfuss et al., Nat. Phys. 11, 820 (2015).  R. Ohta et al., Phys. Rev. Lett 120, 267401 (2018).  R. Ohta et al., Phys. Rev. B 99, 115315 (2019).