A tale of two interfaces: photons and spins linked by a solid-state artificial atom

An electron spin confined to a self-assembled quantum dot presents itself as a natural candidate for the node of a quantum network, offering a highly coherent interface between a solid-state spin and an optical photon. Crucial to the construction of such a network will be the exploitation of the long-lived coherence of the surrounding environment of nuclear spins. This dissertation presents a series of experiments which address some of the challenges of exploiting quantum dots for quantum technologies. First, we implement a new technique for performing coherent control of a spin confined to a quantum dot, achieving the highest control fidelity ever reported in this type of system. The technique is fully flexible, meaning that we can programmatically design control sequences of arbitrary complexity. Next, we use this control technique to mitigate the unwanted effects of the nuclear spin environment on the electron spin. We show that we can tune the rate of coupling to the nuclei, allowing us to protect a known quantum state stored on the electron spin by taking it out of resonance with environmental modes. We then show that we can resolve collective spin-wave modes of the nuclei, each associated with a single spin flip distributed among the ensemble. By probing the coupling frequency between the electron spin and these nuclear modes, we show how to extract information about the population distribution of the nuclear ensemble across its single-particle spin-states. In our case, this procedure reveals the presence of entanglement within the nuclei, manifesting itself as a many-body dark state. Finally, we perform the first spin-control experiments of an electron spin confined to an optically active gallium arsenide quantum dot. We demonstrate coherent control of an electron spin, and probe its coherence via free induction decay and Hahn-echo spectroscopy. The scientific insights and technical knowledge gained from this work could enable the construction of a quantum dot system consisting of a qubit (an electron spin) and a high-fidelity, in situ quantum memory (the ensemble of nuclear spins). This leads towards the assembly of a physically distributed, coherently connected array of quantum dots: a quantum network