Thesis presented March 05, 2024

Abstract:
Bright and tunable sources of indistinguishable single photons are key devices for photonic quantum information technologies. Building such a source with a semiconductor quantum dot (QD) requires a “knob” to tune the QD emission wavelength combined with a broadband photonic structure for light extraction. This thesis reports several important steps towards this goal.
We first investigate a nanocylinder cavity, a photonic structure that, despites its simplicity, offers a pronounced Purcell acceleration of spontaneous emission over a large spectral bandwidth. We demonstrate the first resonant optical spectroscopy of a QD embedded in a nanopost cavity, by leveraging a cross-polarization scheme that efficiently suppresses stray laser light (collaboration with the group of Richard Warburton). This technique enabled a precise characterization of the optical properties of the emitter.
We next demonstrate a tunable single-photon source based on a QD embedded in a tapered photonic wire. In our device, a set of on chip electrodes biased with a DC voltage applies an electrostatic force to the wire. As the wire bends, the resulting mechanical strain changes the bandgap energy of the embedded QDs. We demonstrate both a large increase and a large decrease of the QD emission wavelength by controlling the wire bending direction.
With an AC voltage, the above-mentioned actuation scheme can also excite the vibration modes of the nanowire. This capability is interesting in the context of hybrid nanomechanics. In our experiments, we leverage the QD photoluminescence to detect and identify the wire mechanical vibrations. In particular, we evidence a high-order flexural mode that resonates at 190 MHz, a value that exceeds the QD radiative rate. This constitutes an important step towards the spectrally-resolved-sidebands regime.
The devices demonstrated in this work open promising prospects for the future developments of quantum photonics and hybrid nanomechanics.

Keywords:
Quantum dot, Tunable single photon source, Optical nanocavity, Photonic wire antenna, Mechanical strain, Hybrid nanomechanics