Nanowire quantum dots for quantum photonic technologies

Recent advancements on quantum computing and quantum communication and their promise to revolutionize the world have boosted several research fields. Quantum photonic technologies, such as Quantum Network, are close to becoming real and some market applications have had already their quantum-leap. This thesis is a collection of scientific articles aiming at developing quantum technologies, such as a semiconductor-based quantum network, using novel nanowire quantum dots.

Such structures are expected to provide flexibility and functional advantages over their bulk counterparts. After a brief introduction and background part, the thesis includes: Article I (published)—“AlGaAs and AlGaAs/GaAs/AlGaAs nanowires grown by molecular beam epitaxy on silicon substrates” — reports the growth of AlGaAs nanowires with GaAs insertions to form confined heterostructures (quantum dots).

The details of the growth and the resulting photoluminescence are studied and presented. Article II (submitted) — “Wurtzite AlGaAs nanowires” — shows the first empirical determination of the bandgap of wurtzite AlXGa1−XAs by comparative optical and structural study of samples with different Al content.

Article III (published) — “Nanowire quantum dots tuned to atomic resonances” — presents the detailed study of the emission of nanowire quantum dots in terms of tuning by growth, single-photon quality, and external post-growth frequency-tuning to an atomic frequency, assessing their potential in quantum communication applications.

Article IV (submitted) — “Resonant excitation of nanowire quantum dots” — reports the demonstration of biexciton-exciton cascaded emission via resonant two-photon excitation and resonance fluorescence from an epitaxially-grown GaAs quantum dot in an AlGaAs nanowire, paving the way for exploiting the full potential of nanowire quantum dots for quantum science and technology.

Article V (submitted) — “All-optical charging and charge transport in quantum dots” — proposes a technique for loading and coherent transport of individual charges in a type-II multi-quantum-dot systems, with fidelities greater than 99.9% in few-μs. We also suggest that such structures can be practically realized using, for example, crystal-phase quantum dots in nanowires.