The project bridges the gap between two yet distinct research fields: optomechanics of deformable cavities (cavity optomechanics) and cavity quantum electrodynamics (cavity QED). This project aims at exploring a hybrid interface between these two domains, using semiconductor nanostructures. In particular, we propose the use of a single quantum dot (QD) coupled to a pillar microcavity to study photon-phonon interactions. It has been demonstrated that an optimized optical GaAs/AlAs-based microcavity is automatically an optimized acoustic resonator. This results in a novel platform for optomechanics based on optical micropillars and planar microcavities with optomechanical coupling able to reach 80 THz/nm, working frequencies of the order of 20-200 GHz, and an operating optical wavelength in the NIR range. The confined modes of the pillar microcavity are of very high quality factor (reaching 1 million), and enable a coupling of the cavity photons both to the ~20-GHz mechanical modes of the pillar and to a single InAs QD inserted in the center of the microcavity. In this novel field of research proposed by the project, the aim is to control a coupled tri-partite system: a cavity photon interacts with a coherent quantum emitter (two-level atom) and with a single mechanical mode. First optomechanics experiments relying on the coupling to a QD will be performed: the observation of QD-assisted optomechanical dynamical back-action, leading to the QD-assisted control of the pillar mechanical motion, and then the modification by the pillar mechanical motion of the resonant optical response of a QD in a cavity. We also aim to demonstrate for the first time an engineering of the phonon density of states around a single QD. We will measure the modification of the phonon density of states through the investigation of the phonon assisted emission of a single QD coupled to an optical micropillar cavity.