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Efficient interfaces between photons and quantum emitters form the basis for quantum networks and enable nonlinear optical devices operating at the single-photon level. We demonstrate an integrated platform for scalable quantum nanophotonics based on silicon-vacancy (SiV) color centers coupled to nanoscale diamond devices. By placing SiV centers inside diamond photonic crystal cavities, we realize a quantum-optical switch controlled by a single color center. We control the switch using SiV metastable orbital states and verify optical switching at the single-photon level by using photon correlation measurements. We use Raman transitions to realize a single-photon source with a tunable frequency and bandwidth in a diamond waveguide. Finally, 1 arXiv:1608.05147v1 [quant-ph]

Controllable atomic-scale quantum systems hold great potential as sensitive tools for nanoscale imaging and metrology [1][2][3][4][5][6]. Possible applications range from nanoscale electric [7] and magnetic field sensing [4][5][6]8] to single photon microscopy [1,2], quantum information processing [9], and bioimaging [10]. At the heart of such schemes is the ability to scan and accurately position a robust sensor within a few nanometers of a sample of interest, while preserving the sensor's quantum coherence and readout fidelity. These combined requirements remain a challenge for all existing approaches that rely on direct grafting of individual solid state quantum systems [4,11,12] or single molecules [2] onto scanning-probe tips. Here, we demonstrate the fabrication and room temperature operation of a robust and isolated atomic-scale quantum sensor for scanning probe microscopy. Specifically, we employ a high-purity, single-crystalline diamond nanopillar probe containing a single Nitrogen-Vacancy (NV) color center. We illustrate the versatility and performance of our scanning NV sensor by conducting quantitative nanoscale magnetic field imaging and near-field single-photon fluorescence quenching microscopy. In both cases, we obtain imaging resolution in the range of 20 nm and sensitivity unprecedented in scanning quantum probe microscopy.The NV center in diamond is a point-defect that offers the potential for sensing and imaging with atomic scale resolution. Sensitive nanoscale detection of various physical quantities is possible because the NV center forms a bright and stable single photon source [13] for optical imaging, and possesses a spin-triplet ground state which offers excellent magnetic [5] and electric [7] field sensing capabilities. The remarkable performance of the NV center in such spin-based sensing schemes, is the result of the long NV spin coherence time [14], combined with efficient optical spin preparation and readout [15], all at room temperature. In addition, NV centers can be positioned within nanometers of a diamond surface [16] and therefore in close proximity of a sample to maximize signal strengths and spatial resolution. In order to realize the full potential of these attractive features, we have developed a "scanning NV sensor" (Fig. 1a), which employs a diamond nanopillar as the scanning probe, with an individual NV center artificially created within a few nanometers of the pillar tip through ion implantation. Long NV spin coherence times (≈ 30 µs) are achieved as our devices are fabricated from high purity, single-crystalline bulk diamond [17]. Furthermore, diamond nanopillars are efficient waveguides for the NV fluorescence band [18], which yields record-high NV signal collection efficiencies for a scanning NV device. Fig. 1b shows a representative scanning electron microscope (SEM) image of a single-crystalline diamond scanning probe containing a single NV center. The preparation of such devices is based on recently developed tech- * These authors contributed equally to this work...

The development of a robust light source that emits one photon at a time will allow new technologies such as secure communication through quantum cryptography. Devices based on fluorescent dye molecules, quantum dots and carbon nanotubes have been demonstrated, but none has combined a high single-photon flux with stable, room-temperature operation. Luminescent centres in diamond have recently emerged as a stable alternative, and, in the case of nitrogen-vacancy centres, offer spin quantum bits with optical readout. However, these luminescent centres in bulk diamond crystals have the disadvantage of low photon out-coupling. Here, we demonstrate a single-photon source composed of a nitrogen-vacancy centre in a diamond nanowire, which produces ten times greater flux than bulk diamond devices, while using ten times less power. This result enables a new class of devices for photonic and quantum information processing based on nanostructured diamond, and could have a broader impact in nanoelectromechanical systems, sensing and scanning probe microscopy.

Quantum light emitters have been observed in atomically thin layers of transition metal dichalcogenides. However, they are found at random locations within the host material and usually in low densities, hindering experiments aiming to investigate this new class of emitters. Here, we create deterministic arrays of hundreds of quantum emitters in tungsten diselenide and tungsten disulphide monolayers, emitting across a range of wavelengths in the visible spectrum (610–680 nm and 740–820 nm), with a greater spectral stability than their randomly occurring counterparts. This is achieved by depositing monolayers onto silica substrates nanopatterned with arrays of 150-nm-diameter pillars ranging from 60 to 190 nm in height. The nanopillars create localized deformations in the material resulting in the quantum confinement of excitons. Our method may enable the placement of emitters in photonic structures such as optical waveguides in a scalable way, where precise and accurate positioning is paramount.