Strain-mediated coupling in a quantum dot–mechanical oscillator hybrid system

Recent progress in nanotechnology has allowed the fabrication of new hybrid systems in which a single two-level system is coupled to a mechanical nanoresonator 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 . In such systems the quantum nature of a macroscopic degree of freedom can be revealed and manipulated 10 . This opens up appealing perspectives for quantum information technologies 11 , and for the exploration of the quantum–classical boundary. Here we present the experimental realization of a monolithic solid-state hybrid system governed by material strain 12 : a quantum dot is embedded within a nanowire that features discrete mechanical resonances corresponding to flexural vibration modes. Mechanical vibrations result in a time-varying strain field that modulates the quantum dot transition energy. This approach simultaneously offers a large light-extraction efficiency 13 , 14 and a large exciton–phonon coupling strength g 0 . By means of optical and mechanical spectroscopy, we find that g 0 /2π is nearly as large as the mechanical frequency, a criterion that defines the ultrastrong coupling regime 15 . Coupling of the electronic states in a quantum dot and the vibrations in a nanowire can be achieved by using strain.