Single photons from a trapped-ion cavity-QED system

Quantum networking is an established and growing field of research, with applications in many other fields of quantum technology, as well as fundamental research in quantum mechanics. A quantum network consists of multiple quantum devices that can interchange quantum information or be entangled with each other. Trapped ions coupled to optical cavities are among the most promising platforms in quantum technology broadly and networking specifically, with the ability to initialise and store quantum states in the ions and, via the cavity, transfer those states onto photons, which can interact with distant systems. This thesis describes two experiments using an ion trap with integrated high finesse optical cavity as a source of single photons. In the first, the photons were converted to a standard telecommunications wavelength through quantum frequency conversion and transmitted over 10 km of optical fibre. The attenuation experienced by the photons in optical fibre without frequency conversion would make transmission over such a long distance impractical. The converted photons were shown to maintain their nonclassical statistics, meaning such a system could be used to create quantum networks over long distances. A novel scheme for producing single photons from the ion-cavity system was demonstrated. This scheme significantly reduces the impact of decoherence in the system compared to commonly used schemes through selection of the initial state of the ion. This scheme may be directly applied to ion-photon entanglement and would lead to improved fidelity in ion-ion entanglement or state transfer. Both experiments represent significant steps towards the building of quantum networks based on ions coupled to optical cavities. They lay the groundwork for future experiments using the same system to entangle ions with photons and eventually with ions in other traps.