Nanophotonic cavities are a special type of optical resonators which have dimensions in the order of tens to hundreds of nanometers. They are usually implemented with incorporating Bragg reflectors/controlled index variations in the photonic structures. Nanophotonic cavities can strongly confine light/photon, and thus, can significantly enhance photon generation and collection probability from any emitter placed inside the cavity. This unique properties can be used for enhancing the radiative decay rate of a diamond color center emitter, suppressing non-favorable transitions, improving the coherence and spectral purity, spin-photon entanglement generation efficiency, etc. All of these are critical for efficient qubit readout, remote entanglement and large scale diamond based quantum computer, network system implementation. However, fabricating such nanophotonic cavities accurately in diamond is challenging and requires careful testing to achieve optimum yield & performance. In this project, we will design and implement an optical characterization setup in order to test and improve the nanophotonic cavities fabricated for realizing diamond based quantum computers.
 Ross Schofield, PhD Thesis, Imperial College London, 2021