Nanowire-based Quantum Photonics

Abstract

In this thesis work, I studied individual quantum dots embedded in one-dimensional nanostructures called nanowires. Amongst the effects given by the nanometric dimensions, quantum dots enable the generation of single light particles: photons. Single photon emitters and detectors are central building blocks of future communication technologies. As the miniaturization in electronics is driving towards the quantum limit, we envision future telecommunication as based on single photons. Single photons enable the use of quantum properties of light to encode information and share it with unbreakable security provided by quantum cryptography. Based on the principle that a single photon cannot be cloned and that its quantum state cannot be observed without altering it the information that the photon is carrying, a single particle of light represents the ideal mean of transportation for future secure telecommunication. During my work, nanowires have been tailored into waveguides providing directional propagation along the nanostructure that out-couples to the macroscopic world with negligible losses. The optical properties of the quantum dots have been explored through photoluminescence spectroscopy and improved in order to obtain a pure flux of single photons. Simultaneously, the material composition and shape of the nanowire have been designed to achieve efficient collection of these photons. Nanowires are tailored into waveguides providing directional propagation along the nanostructure that out-couples to the macroscopic world with negligible losses. This system we developed can be seen as an analogue of an nano optical fiber where photons are propagating one at a time. Several optical properties of the emitted single photons have been analyzed and subsequently optimized such as the temporal emission statistics, the shape and dispersion of the energy spectrum and the spatial emission profile. In addition, we demonstrated the possibility of creating an excitation in the quantum dot and translate this excitation into an electrical signal transmitted along the nanowire, thereby detecting the generation of individual excitations in the nanostructure.