High-Order Nanowire Resonances for High-Frequency, Large-Coupling-Strength Quantum Dot Hybrid Nanomechanics

Hybrid nanomechanical systems embedding a quantum light emitter, such as a semiconductor quantum dot (QD), are actively investigated both for their fundamental interest and for potential applications to quantum information technologies. Here, we explore the high-order vibration modes of a conical GaAs nanowire that embeds a few self-assembled InAs QDs. On-chip electrodes generate a 3D force field that can drive flexural and longitudinal vibration modes. Mechanical vibrations are detected optically by measuring the microphotoluminescence spectrum of the QDs. The latter also provides a fingerprint of the mode nature. Starting from the sub-MHz fundamental flexural mode, we show that higher-order resonances enable a dramatic increase in both mechanical frequency and hybrid coupling strength. In particular, we identify a low-loss flexural mode that resonates at 190 MHz. This frequency exceeds the QD radiative rate, which constitutes an important step toward the resolved-sideband regime. For a QD located at the stress maximum, the hybrid coupling strength reaches 3.9 MHz, the highest value reported so far for a QD hybrid system. These results demonstrate the potential of the QD-nanowire platform for high-frequency hybrid nanomechanics.