Zoom link: https://upenn.zoom.us/j/94300725438?pwd=ULEYFh03w6gJQemJJ1rx6HlaPA2kZn.1

Solid-state spin defects are a versatile class of systems for emerging quantum technologies. This thesis focuses on the optical interfacing of such defect platforms. In the first half of the thesis, a photonic inverse design methodology called many-body shape optimization is implemented in order to design a metasurface optical interface for the nitrogen-vacancy (NV) center in diamond. This metasurface enhances the collection efficiency of single photons emitted by the NV center, which is essential for efficient readout of the spin-qubit state. The metasurface additionally collimates the photon-emission spatial mode in order to obviate the need for expensive and bulky free-space optics and enable a more scalable interface. The inverse design method itself is broadly applicable to other defect systems and to other photonic design problems. The second half of the thesis focuses on the experimental investigations of europium-doped gallium nitride (GaN:Eu). Rare earth ions such as Eu are known for their narrow homogeneous optical linewidths and long spin coherence times, making them particularly attractive spin-photon interfaces for building quantum memories. In contrast with typical complex oxide host materials for rare-earth ions, GaN is a technologically robust platform, allowing for easier integration with nanostructured photonic and electronic elements and providing new opportunities for initialization and readout utilizing indirect excitation. An experimental apparatus is developed for optical imaging of GaN:Eu that includes a pulsed UV laser for indirect excitation as well as a widely- and precisely-tunable, narrow-linewidth OPO source to address sub-ensembles with MHz linewidths. It is demonstrated that delta-doped of Eu in GaN can enhance and isolate specific Eu³⁺ incorporation sites and can be tuned to yield favorable device properties for classical or quantum applications. Finally, characterization of key properties including linewidths and coherence times are discussed in order to validate GaN:Eu as a viable platform for quantum technologies, with preliminary measurements yielding comparable results to Eu in other substrates.