Coherent control of single spins in diamond

Diamond-based materials have recently emerged as a unique platform for quantum science and engineering\footnote{D.D. Awschalom, R.J. Epstein, and R. Hanson, Scientific American 297, 84 (2007).}. Spins of single Nitrogen-Vacancy (N-V) color centers in diamond can be imaged, initialized and read out optically. These N-V center spins may allow for quantum information processing at room temperature, as measurements have shown long room-temperature electron spin coherence times well into the microsecond regime. We have investigated single N-V center spins that are coupled to electron spins of nearby nitrogen (N) defects, using magneto- optical imaging and coherent single-spin control at room temperature. Some of the N-V centers are strongly coupled to only one single N spin, allowing the controlled polarization and readout of this single `dark' N spin. In contrast, other N- V centers couple to many N spins. We use these latter systems to study the canonical decoherence model of a single central spin coupled to a spin bath. By tuning the internal bath dynamics as well as the spin-bath coupling, we gain access to regimes with strikingly different behaviour. Finally, we have fabricated and characterized photonic crystal microcavities in poly-crystalline diamond and observed quality factors up to 600 \footnote{C.F. Wang, R. Hanson, D.D. Awschalom, E.L. Hu, T. Feygelson, J. Yang, J. E. Butler, Appl. Phys. Lett. 91, 201112 (2007).}. These structures are a first step towards controllable coupling of single N-V spins to single photons in a cavity-QED system in diamond.