AQOUSTIQS

Quantum acoustics – control over mechanical motion at the single-phonon level – is an exciting research frontier. This emerging field addresses very fundamental questions, such as the exploration of the boundaries between the quantum and classical realms. From a more applied perspective, single phonons may offer a novel way to distribute quantum information on a chip. In this vibrant context, coupling a two-level system to a mechanical resonator represents a powerful strategy to gain exquisite control over mechanical motion. Furthermore, building such a so-called hybrid nanomechanical system with an optically-active artificial atom opens unique opportunities, including a direct access to the phonon statistics. In this endeavor however, reaching the strong coupling regime and taming thermal mechanical decoherence both represent major challenges. Our consortium has made pioneering contributions to the field, by strain-coupling a semiconductor quantum dot to a vibrating microwire. Recently, we succeeded in driving the vibration of the microwire from the resonant optical excitation of a single quantum dot. In this experiment, the system however still operates far from the strong coupling condition, and the induced vibration is purely classical. In addition, the low frequency of the vibrational mode (below 1 MHz) imposes a very long averaging time to get rid of thermal fluctuations. Therefore, the optical generation of long-lived quantum states of motion remains a considerable challenge, which calls for a new generation of devices, with massively improved performance. The project AQOUSTIQS will demonstrate strain-mediated hybrid systems that operate deep in the quantum regime. To enable coherent optical manipulation, both the mechanical frequency and the coupling strength will be brought above the radiative decay rate of the quantum dot (~160 MHz). To maximize the chance of success, device development will follow two parallel tracks: (1) evolving the current generation of systems, in which a new actuation technique has recently revealed low-loss vibrational modes approaching the GHz limit, and (2) developing a new, ultra-low dissipation double cavity nanowire heterostructure operating in the 10 GHz range. As a first step into the realm of quantum hybrid optomechanics, we will prepare single-phonon Fock states. Thanks to a built-in phonon-to-photon transduction, the quantum nature of this mechanical state will be directly evidenced using established quantum optics techniques. We will also demonstrate the elementary exchange of single phonons between two quantum dots embedded in the same resonator. On the way to achieve its objectives, the project AQOUSTIQS will experimentally address several fundamental questions, including the nature of the noise processes in solid-state quantum dots at the single phonon level. Once completed, AQOUSTIQS will set the ground for a possibly-coherent mechanical link between various quantum dots. From a technological point of view, the project will also give birth to a coherent interface between flying photons and a long-lived mechanical resonator, with possible, future applications to quantum technologies.