This thesis is focused on the negatively charged nitrogen-vacancy (NV --) center in diamond and the neutral divacancy (VV0) in silicon carbide (SiC), two optically addressable atom- sized defects with remarkable properties. They have the ability to sense temperature, electric, and magnetic fields, and can be integrated into tiny nanoparticles and placed in otherwise inaccessible places, such as inside of living cells. Their electronic quantum spin state can be initialized and read out with laser light and coherently manipulated by microwave irradiation. Additionally, these defects possess long coherence times, a measure of how long they can maintain their quantum state and an important metric for applications from sensing to quantum internets, even at room temperature. This thesis covers the NV center in diamond and investigates ways to improve the sensitivity of these defects to temperature and magnetic and electric fields using special patterns of light, microwave, and radio frequency pulses. In particular, these experiments demonstrate that the diamond nitrogen-vacancy center can be a sensitive thermometer (&eegr; ∼ 10mK/Hz1/2) over a wide range of temperatures up to 600 K with nanoscale spatial resolution.

Another exciting prospect for their use is in the field of quantum information. The advent of quantum computing, in which information is not stored in binary 0's and 1's but instead as a complex mixture of these, promises to solve certain problems exponentially faster than classical computers. While there is an intense ongoing research effort into building quantum computers that can outperform their classical counterparts, work has already begun on designing a future quantum internet to connect them. These networks rely on the resource of entanglement to transmit quantum information, but in order to entangle one defect with another, their properties must first be tuned into resonance. The other part of this thesis addresses some of the hurdles that remain in using the divacancy as a functional node in a quantum information network, including tuning them to emit identical photons.