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Saptarshi Kotal

Controlling the spectral properties of quantum light sources based on a quantum dot in a nanowire

Published on 17 June 2021
Thesis presented June 17, 2021

This work aims at controlling the spectral properties of the photons that are emitted by a semiconductor quantum dot (QD) embedded in a photonic nanowire antenna. First, we conduct a theoretical study which unveil a new decoherence mechanism in this system. We show that, even at cryogenic temperature, the thermal vibrations of the nanowire induce a large spectral broadening that prevents the emission of indistinguishable photons. We propose three designs that suppress this decoherence channel thanks to an engineering of the nanowire mechanical properties. Next we introduce a nanowire optical nanocavity which offers a large acceleration of spontaneous emission (predicted Purcell factor of 6.3) that is maintained over a 30-nm-wide operation bandwidth. We fabricate a GaAs nanocavity which embeds InAs self-assembled QDs. Single QD spectroscopy reveals a maximal acceleration of spontaneous emission by a factor as large as 5.6 and a first lens collection efficiency of 0.35. Finally, we propose a strategy to tune the emission wavelength of a QD embedded in a nanowire antenna. On-chip electrodes generate an electrostatic force that bends the nanowire. The resulting strain modulates the QD bandgap energy. We realize a first generation of devices and discus preliminary wavelength tuning measurements. Overall, these results open promising perspectives for photonic quantum technologies, in particular for the realization of advanced sources of quantum light.

Semiconductor quantum dot, Photonic wire antenna, Optical nanocavity, Purcell effect, Mechanical vibrations, Mechanical strain, Single photon sources, Quantum information technologies, Quantum optics

On-line thesis.