"A Nano-OptoMechanical System (NOMS) is an ideal interface between nanomechanical motion and photons. The merits of such a system depend crucially on the level of optical/mechanical coupling. For sufficient coupling, the nanomechanical motion is efficiently imprinted on photons and read-out with the assets of optical detection: broadband, fast, ultra sensitive (ultimately quantum limited). Moreover, in a NOMS, the very dynamics of the motion (its frequency, damping, noise spectrum) can be controlled by optical forces. This opens novel roads for nanomechanical sensing experiments, both classical or quantum, that need now to be experimentally investigated and brought in compliance with future on-chip applications.This project relies on Gallium-Arsenide (GaAs) disk optomechanical resonators, where photons are stored in high quality factor optical whispering gallery cavities and interact with high frequency (GHz) nanomechanical modes. We have recently shown that these resonators possess a record level of optomechanical coupling and are compatible with on-chip optical integration. The first aim of the project is to investigate in depth the mechanisms leading to optical and mechanical dissipation in GaAs nanoresonators, and obtain GaAs NOMS with ultra-low dissipation. The second aim is to realize prototype nano-optomechanical force measurements with a GaAs disk resonator set in optomechanical self-oscillation, to establish the potential of this novel approach for sensing. This will be done both under vacuum and in a liquid. The behavior of two NOMS integrated on the same chip will also be studied, as first archetype of parallel architectures. A third aim is to operate GaAs NOMS at their quantum limit, using cryogenics, optomechanical cooling and novel concepts where an active optical material like a Quantum dot or Quantum well is inserted in the GaAs NOMS to enhance optomechanical interactions. Transfer of quantum states within a QD-NOMS coupled system will be explored."