### Session S1: Diamond-based Quantum Information Processing

 Wednesday, March 12, 2008 2:30PM - 3:06PM S1.00001: Coherent control of single spins in diamond Invited Speaker: Ronald Hanson 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. Wednesday, March 12, 2008 3:06PM - 3:42PM S1.00002: Controlling individual electron and nuclear spins in diamond: from quantum registers to applications Invited Speaker: Mikhail Lukin We will discuss our recent work involving the controlled manipulation of individual electron and nuclear spins in a high-purity diamond lattice. Our approach combines ideas from single molecule spectroscopy, quantum optical control techniques and the physics of mesoscopic spin ensembles. It allows us to isolate, polarize and manipulate single nuclear spins and use them to create quantum memory and small quantum registers with exceptional coherence properties, even under ambient room temperature conditions. We will also describe novel applications of these techniques, including new approaches to quantum communication and computation as well as new quantum magnetic sensors with nanoscale resolution. Recent progress towards realization of these ideas will be discussed. Wednesday, March 12, 2008 3:42PM - 4:18PM S1.00003: Fabrication Strategies for Practical Diamond Based Quantum Information Processing Devices Invited Speaker: Steven Prawer Optically emitting defect centres in diamond display a range of unique quantum properties that offer exciting possibilities for the construction of quantum devices which employ optical single-spin read-out. Indeed diamond is an ideal material for use in the fabrication of (i) single photon sources for quantum communications, (ii) optical fibre-based single spin read out systems, (iii) photonic platforms for the investigation of quantum entanglement in solid state systems and (iv) optical regenerators and non-linear quantum gates. The toolkit of available fabrication strategies which are used to engineer devices taking advantage of these unique properties will be presented. Our most recent results include demonstrations of (i) optical fibre based single photon sources based on Nickel and Nitrogen optical centres, (ii) waveguiding of light in structures hewn from single crystal diamond, (iii) Electrical Stark shift of the frequency of single optical emitters, (iv) coupling between the spins between single NV and N atoms in devices engineered by ion implantation, and (v) electromagnetically induced transparency in single NV centres. These crucial demonstrations establish the feasibility of a defect tolerant architecture for the fabrication of a few ($\sim$10-50 ) qubit diamond based quantum information processor. We will present one such possible architecture and explain the specific role for ion beam processing in the creation of qubits and the engineering of diamond photonic devices. Wednesday, March 12, 2008 4:18PM - 4:54PM S1.00004: Coherent Population Trapping of Single Spins in Diamond under Optical Excitation Invited Speaker: Charles Santori The nitrogen-vacancy (N-V) center in diamond has long-lived electronic and nuclear spin coherence combined with optical addressability, making it an attractive candidate system for building a photonic network for quantum information applications. However, realizing such schemes will require control over the N-V energy level structure and integration into high-quality microphotonic structures operating at visible wavelengths. In this talk I will describe experiments on optical manipulation of N-V centers in low-nitrogen diamond samples. Typically the optical transitions of NV$^{-}$ are spin-conserving, so that if the N-V begins in the m$_{s}$=0 ground state, it can undergo many optical excitation/fluorescence cycles before transitioning to m$_{s}=\pm$1. However, by applying stress to the crystal, or by using strain already present, it is possible to realize a $\Lambda$-type system with one excited state coupled by optical transitions to multiple ground states. By this technique we have observed coherent population trapping both in N-V ensembles and in single N-V centers. These results demonstrate the potential for all-optical spin manipulation in this system. I will also describe initial work on coupling N-V centers to photonic structures with the goal of enhancing emission into the zero-phonon line, as needed for applications such as quantum repeaters. Wednesday, March 12, 2008 4:54PM - 5:30PM S1.00005: Controlling single defects: Electric and magnetic fields Invited Speaker: Joerg Wrachtrup Controlling the optical properties of single defects, e.g. its transition frequency and transition properties is an important prerequisite for their broad application. It is shown that external electric and magnetic fields allow for control over a broad range of parameters. The optical transition frequency can e.g. controlled by an electric field. The same field also determines whether the defect is driven cyclic or lambda transition behaviour dominates. The talk will describe out current knowledge of the defect in this respect and show perspectives toward cavity coupling and entanglement of distant defects.