UC Santa Barbara

Solid-state spins with controlled dipolar interactions constitute a powerful platform for quantum technologies. Ensembles of coherent spins with tunable density and controlled dimensionality provide a starting point for investigating strongly interacting spin systems in which novel, many-body states can arise and enable several advancements in quantum sensing and simulation such as interaction-driven localization or dipolar-driven spin squeezing. Engineering control over spin-spin interactions is a necessary but challenging task in order to realize these applications. Defects spins in diamond, such as nitrogen-vacancy (NV) centers, represent a promising platform to explore due to their rich recent history of investigation and development. However, outstanding challenges include the creation of dense, two-dimensional NV ensembles, engineering their nonzero dipolar interactions, and controlling surface proximity for metrological utility.In this dissertation, we demonstrate that delta doping during plasma-enhanced chemical vapor deposition (PECVD) diamond growth provides a key route to achieving control over dimensionality and the dominance of desired dipolar interactions. We present the creation of high-density, two-dimensional NV and nitrogen layers and explore the mechanisms of growth and dopant incorporation in (001)-oriented diamond. We pioneer the creation of 2D, strongly interacting dipolar ensembles in (111)-oriented diamond, which though minimally explored to date, provide unique advantages for quantum technologies that cannot be achieved with 3D ensembles or (001)-oriented diamond. We show that growth on the (111) plane affords maximally positive dipolar interactions among a 2D NV ensemble, which is crucial for leveraging dipolar-driven entanglement schemes and exploring new interacting spin physics. Additionally, we uncover a method to increase the density of grown-in, preferentially aligned NV centers, resulting in the creation of NV ensembles with a high magnetic sensitivity, and we extend these methods to engineer NV centers with close proximity to the diamond surface for high spatial resolution sensing.Altogether, this work combines a rigorous materials approach with qubit-based measurements to realize strongly interacting NV ensembles in diamond. We demonstrate foundational advancements in diamond materials synthesis, which facilitate control over NV density, dimensionality, coherence, and interactions. The capabilities we have developed are leveraged by NV applications across diverse fields from 2D magnetism to optomechanics, ultimately enabling the pursuit of new frontiers in quantum sensing and simulation in the solid state.