The nitrogen-vacancy (NV) center is a point defect in the diamond crystal lattice, forming a localized-electron system with unique optical and spin properties. In particular, optical control and read-out of the spin state, combined with long spin coherence times, make it an attractive candidate for both high-sensitivity magnetometry and as a solid-state spin qubit for quantum information processing (QIP). This dissertation documents the design, implementation, and characterization of systems aimed at each of these applications.;First, the development of a GaP-on-diamond integrated photonics platform for QIP is presented. This work is motivated in part by the scalability advantages that are inherent to photonic device integration, and more fundamentally by the large potential improvements in performance. Specifically, coupling NV centers to integrated optical resonators should enable orders of magnitude improvement in entanglement generation rate through improved photon collection efficiency. This will be crucial for the development of even small-scale QIP systems, as NV-NV spin entanglement has so far only been demonstrated at rates far below the spin decoherence rate, effectively limiting NV-based QIP to two-qubit systems. Large numbers of integrated optical devices were fabricated, including optical resonators. Passive transmission measurements were performed on hundreds of individual devices, enabling statistical performance metrics and device yields to be extracted for several components. Device-coupled single-photon measurements are also presented, indicating photon collection efficiencies as high as 9%, corresponding to an efficiency-limited entanglement rate far exceeding the best reported spin decoherence rate. These results put the GaP-on-diamond platform in a competitive position relative to other photonic integration efforts for QIP.;Next, a magneto-optical microscope for bio-sensing applications is presented. The microscope images photoluminescence emitted from a thin, dense sheet of NV centers within the top 200 nm of a diamond chip. Changes in the photoluminescence associated with the spin population of the defects allow for optically detected magnetic resonance (ODMR), with the resonant frequency depending on the local magnetic field. Two-dimensional images of the magnetic field at the surface of the diamond are thus obtained, with a magnetic field sensitivity of 2.4 muT. The microscope was able to detect magnetic-field disturbances due to the presence of single 19-nm-diameter super-paramagnetic nanoparticles (SPNs) in wide-field ODMR images taken at room temperature. This is the first demonstration of wide-field detection of individual sub-mum magnetic particles under ambient conditions, and should enable a new class of biological imaging and sensing systems based on SPN labels.
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