Over the last decades, researchers developed exquisite control over the quantum state​ of various real or artificial atoms. Is it possible to extend this control to a much larger object, such as a mechanical resonator? The generation of quantum states of motion in a “macroscopic” oscillator is first motivated by pure curiosity. In a more applied perspective, this capability would also open new opportunities for quantum information technologies. To achieve this ambitious goal, one promising strategy is to couple the mechanical resonator to an atomic-like system.

Together with colleagues at Institut Néel (Grenoble, France) and Laboratoire Lumière Matière et Interfaces LuMin (Orsay, France), our team pioneered a semiconductor device based on a vibrating microwire embedding a single quantum dot (QD). The latter is a nanometer-scale insertion of indium arsenide in a gallium arsenide crystal. At liquid-helium temperature, this nanostructure features discrete energy levels and remarkable optical properties, very much like a real atom. In addition, its emission wavelength is extremely sensitive to the deformation of the crystal lattice, resulting in a large, built-in coupling to mechanical vibration. Early studies focused on the fundamental, sub-megahertz resonance of the microwire, which behaves as a classical oscillator. Entering the quantum regime calls for a massive increase in the mechanical frequency. This is in particular required to minimize the impact of thermal fluctuations, and to enable the all-optical control and detection of mechanical motion.

Our team developed a new device in order to explore the high-frequency mechanical resonances of the microwire (Fig. a). Mechanical drive is here provided by a set of on-chip electrodes, which applies an oscillating electrostatic force to the microwire. A few distinct QDs, located near the wire base, probe the wire vibration. The latter modulates the QDs emission wavelength, leading to a spectral broadening of their optical emission ( Fig. b). Experiments revealed a high-order flexural resonance with a frequency as high as 190 MHz, one thousand times larger than the one of the fundamental mode. Interestingly, the associated mode shape features many spatial oscillations, which considerably increases the bending deformation experienced by the QD (Fig. c). As a result, the coupling strength to the vibration mode reaches a record value for a QD-based system.

These findings pave the way towards the optical generation of quantum state of motion and the realization of coherent opto-mechanical interfaces. Such exciting prospects will be explored in the frame of The French ANR project AQOUSTIQS. It will gather the above-mentioned partners and will be launched early 2025.