Nitrogen-vacancy (NV) defect centers in diamond have generated much interest for their uses in quantum information and sensing. Despite the ongoing improvements in sensitivity and the range of new applications, much about the NV basic physics remains unresolved, which is important to understand in order to fully exploit potential uses. In this work I describe a series of experiments on NV basic properties, applications, and projects in between. First, I describe an NV singlet absorption spectroscopy experiment, which searched for additional NV electronic states and studied the 1A1 phonon modes. Next, I discuss an NV microwave saturation spectroscopy experiment, which is useful for NV thermometry, removes inhomogeneous broadening, and can yield information about diamond magnetic spin bath dynamics. I then describe an NV relaxation experiment that senses GHz-frequency magnetic noise, which we demonstrated using paramagnetic substitutional nitrogen (P1) centers. Finally, I describe open questions on the NV singlet states, saturation spectroscopy, and relaxation (and how to address them), and report on my ongoing work on using NVs for nuclear polarization and rotation sensing.
Basic Properties of Strong Mixing Conditions. A Survey and Some Open Questions