The research in cavity optomechanics has recently achieved a major breakthrough: the first observation of quantum phenomena in cryogenic, optically cooled mechanical resonators (i.e., actually in macroscopic objects), as well as in the electromagnetic field interacting with such resonators. These results open the way to the exploitation of optomechanical systems as quantum sensors. The main target of this project is indeed the creation of optomechanical sensing devices achieving the quantum limit in the measurement process, and exploiting peculiar quantum properties, of both the mechanical oscillator and the interacting radiation field, to enhance the efficiency of the measurement and to integrate the extracted information in quantum communication systems. We will develop three different platforms that, according to the present state of the art, are the most suitable to achieve our goal: (i) semiconductor nano-optomechanical disks (ii) tensioned dielectric membranes (iii) levitating nanoparticles. This parallel approach allows increasing the success probability, to extend the operating frequency range and diversify the systems for a larger versatility. Moreover, in order to study specific quantum protocols, we will exploit nano-electro-mechanical systems which have been shown to be the most suitable classical test-bench for this purpose thanks to their long coherence even at room temperature and their unprecedented control. Mechanical and optical properties of the different resonators will be improved, choosing innovative paths to advance the state of the art, in order to increase the coherent coupling rate and reduce the decoherence rate, eventually achieving quantum performance of the devices at room temperature, a crucial requirement for a realistic application scenario as sensors. Producing and manipulating quantum states of a sensor is an important pre-requisite for the quantum revolution, e.g., for implementing a quantum network that collects information from the environment and transfers it into quantum communication channels. We will produce prototype portable sensing systems, evaluate and compare the performance of the different platforms as acceleration sensors, study the possibilities of system integration and of functionalization for future extended sensing capability. Our goal is reaching a quantum performance in optomechanical sensors under room temperature operation. Hence, concerning the Target Outcomes specified in the Call document, we mainly refer to the area 5 (Quantum metrology sensing and imaging), and address in particular the issue “Implementation of micro- and nano- quantum sensors, for instance for quantum limited sensitivity”. In the same area, also the aspects “Use of quantum properties for … accelerometry, and other applications”, and “ Development of detection schemes that are optimised with respect to extracting relevant information from physical systems” are of interest. In addition, we see a close connection to area 6 (Novel ideas and applications in quantum science and technologies), concerning the study of “Quantum phenomena, such as superposition and entanglement, as means to achieve new or radically enhanced functionalities.” We aim indeed at exploring how entanglement between mechanical and radiation states can produce radically new (and more efficient) measurement protocols, and eventually the storage of the measurement results into a field state working as transportable quantum variable. This last issue also involves area 1 (Quantum communication). Finally, the quantum optomechanical system can also contribute to the area 4 (Quantum information sciences) for what concerns the “Novel sources of non-classical states and methods to engineer such states”, since such states can indeed be produced thanks to the optomechanical interaction.