Hybrid quantum systems have recently attracted growing interest from researchers in various fields, with the prospect of combining the advantages different quantum systems while compensating for their individual weaknesses. In this dissertation, we explore a monolithic hybrid system based on single-crystal diamond (SCD) mechanical resonators and the embedded nitrogen-vacancy (NV) centers qubits. To connect the two systems, the inherent strain fields act as the means of coupling, which, importantly eliminates the need for resonator functionalization. In this hybrid architecture, the coherent and manipulable NV center can be used as a quantum bit, while the sensitivity of the mechanical resonator to various fields can be utilized as a quantum interface to other disparate quantum systems. However, despite the promising prospects of such a monolithic NV center-mechanical resonator system, challenges in single-crystal diamond fabrication while maintaining the coherent quantum properties of the NV center have limited its realization. Furthermore, the strain sensitivities of the NV center have also not been well studied due to the lack of a high-quality diamond mechanical platform.

To address these previous limitations, this dissertation will discuss techniques for fabricating high-quality SCD mechanical resonators and further, the utilization of these resonators to both study NV center strain coupling and exert control over the NV's spin and orbital states. SCD mechanical resonators were fabricated using a diamond-on-insulator (DOI) platform, which was developed using a wafer-bonding-based technique. The fabricated SCD resonators were found to have high quality factors of over 300,000 at room temperature, and the spin properties of the embedded NV centers were maintained. Using the controlled strain field generated by the resonator's deflections, the strain sensitivities of both the NV's ground state spin and excited state transitions were studied on the individual NV basis. We demonstrated dynamic coupling of the AC strain to the resonator spins, as well as coherent modulations of the NV center's optical transitions. Utilizing our advancements in diamond fabrication and the resulting improved understanding of the strain sensitivity in NV centers, we discuss the future developments needed to reach the quantum regime of coupling.