We report the detection and polarization of nuclear spins in diamond at room temperature by using a single nitrogen-vacancy (NV) center. We use Hartmann-Hahn double resonance to coherently enhance the signal from a single nuclear spin while decoupling from the noisy spin bath, which otherwise limits the detection sensitivity. As a proof of principle, we (i) observe coherent oscillations between the NV center and a weakly coupled nuclear spin and (ii) demonstrate nuclear-bath cooling, which prolongs the coherence time of the NV sensor by more than a factor of 5. Our results provide a route to nanometer scale magnetic resonance imaging and novel quantum information processing protocols.

Bulk (13)C polarization can be strongly enhanced in diamond at room temperature based on the optical pumping of nitrogen-vacancy color centers. This effect was confirmed by irradiating single crystals at a ~50 mT field promoting anticrossings between electronic excited-state levels, followed by shuttling of the sample into an NMR setup and by subsequent (13)C detection. A nuclear polarization of ~0.5%--equivalent to the (13)C polarization achievable by thermal polarization at room temperature at fields of ~2000 T--was measured, and its bulk nature determined based on line shape and relaxation measurements. Positive and negative enhanced polarizations were obtained, with a generally complex but predictable dependence on the magnetic field during optical pumping. Owing to its simplicity, this (13)C room temperature polarizing strategy provides a promising new addition to existing nuclear hyperpolarization techniques.

Polarizing nuclear spins is of fundamental importance in biology, chemistry and physics. Methods for hyperpolarizing 13C nuclei from free electrons in bulk usually demand operation at cryogenic temperatures. Room temperature approaches targeting diamonds with nitrogen-vacancy centres could alleviate this need; however, hitherto proposed strategies lack generality as they demand stringent conditions on the strength and/or alignment of the magnetic field. We report here an approach for achieving efficient electron-13C spin-alignment transfers, compatible with a broad range of magnetic field strengths and field orientations with respect to the diamond crystal. This versatility results from combining coherent microwave- and incoherent laser-induced transitions between selected energy states of the coupled electron–nuclear spin manifold. 13C-detected nuclear magnetic resonance experiments demonstrate that this hyperpolarization can be transferred via first-shell or via distant 13Cs throughout the nuclear bulk ensemble. This method opens new perspectives for applications of diamond nitrogen-vacancy centres in nuclear magnetic resonance, and in quantum information processing.

We experimentally demonstrate the manipulation of optical diffraction, utilizing the atomic thermal motion in a hot vapor medium of electromagnetically-induced transparency (EIT). By properly tuning the EIT parameters, the refraction induced by the atomic motion may completely counterbalance the paraxial free-space diffraction and by that eliminates the effect of diffraction for arbitrary images. By further manipulation, the diffraction can be doubled, biased asymmetrically to induced deflection, or even reversed. The latter allows an experimental implementation of an analogy to a negative-index lens.Any image, imprinted on a wave field and propagating in free space, undergoes a paraxial diffraction spreading and eventually blurs. In many disciplines, the possibility to reduce or manipulate the diffraction is explored, for purposes such as imaging, wave guiding, microlithography, and all-optical light processing. As was recently demonstrated, arbitrary images can be imprinted on light pulses which are dramatically slowed when traversing a medium of room-temperature atoms [ 1,2], via the process of electromagnetically induced transparency [ 3,4]. In addition to the regular free-space diffraction, the slow-light images undergo diffusion due to the thermal atomic motion [ 5,6]. Here we report an experimental demonstration of a novel technique to eliminate

Detecting and controlling nuclear spin nano-ensembles is crucial for the further development of nuclear magnetic resonance (NMR) spectroscopy and for the emerging solid state quantum technology.Here we present the fabrication of a ≈ 1 nanometre thick diamond layer consisting of 13 C nuclear spins doped with Nitrogen-Vacancy centres (NV) embedded in a spin-free 12 C crystal matrix. A single NV in the vicinity of the layer is used for polarization of the 13 C spins and the readout of their magnetization. We demonstrate a method for coherent control of few tens of nuclear spins by using radio frequency pulses and show the basic coherent control experiments -Rabi oscillations, Ramsey spectroscopy and Hahn echo, though any NMR pulse sequence can be implemented. The results shown present a first steps towards the realization of a nuclear spin based quantum simulator. *

The strong driving regime occurs when a quantum two-level system is driven with an external field whose amplitude is greater or equal to the energy splitting between the system's states, and is typically identified with the breaking of the rotating wave approximation (RWA). We report an experimental study, in which the spin of a single nitrogen-vacancy (NV) center in diamond is strongly driven with microwave (MW) fields of arbitrary polarization. We measure the NV center spin dynamics beyond the RWA, and characterize the limitations of this technique for generating high-fidelity quantum gates. Using circularly polarized MW fields, the NV spin can be harmonically driven in its rotating frame regardless of the field amplitude, thus allowing rotations around arbitrary axes. Our approach can effectively remove the RWA limit in quantum-sensing schemes, and assist in increasing the number of operations in QIP protocols.

We report on a theoretical and experimental study of time-optimal construction of arbitrary singlequbit rotations under a single strong driving field of finite amplitude. Using radiation-dressed states of nitrogen vacancy centers in diamond we realize a strongly-driven two-level system, with driving frequencies four times larger than its precession frequency. We implement time optimal universal rotations on this system, characterize their performance using quantum process tomography, and demonstrate a dual-axis multi-pulse control sequence where the qubit is rotated on time scales faster than its precession period. Our results pave the way for applying fast qubit control and high-density pulse schemes in the fields of quantum information processing and quantum metrology.

Self-similar solutions of the coherent diffusion equation are derived and measured. The set of real similarity solutions is generalized by the introduction of a nonuniform phase surface, based on the elegant Gaussian modes of optical diffraction. In an experiment of light storage in a gas of diffusing atoms, a complex initial condition is imprinted, and its diffusion dynamics is monitored.The self-similarity of both the amplitude and the phase pattern is demonstrated, and an algebraic decay associated with the mode order is measured. Notably, as opposed to a regular diffusion spreading, a self-similar contraction of a special subset of the solutions is predicted and observed.Typeset by REVT E X 1