Fluorescent particles are routinely used to probe biological processes. The quantum properties of single spins within fluorescent particles have been explored in the field of nanoscale magnetometry, but not yet in biological environments. Here, we demonstrate optically detected magnetic resonance of individual fluorescent nanodiamond nitrogen-vacancy centres inside living human HeLa cells, and measure their location, orientation, spin levels and spin coherence times with nanoscale precision. Quantum coherence was measured through Rabi and spin-echo sequences over long (>10 h) periods, and orientation was tracked with effective 1° angular precision over acquisition times of 89 ms. The quantum spin levels served as fingerprints, allowing individual centres with identical fluorescence to be identified and tracked simultaneously. Furthermore, monitoring decoherence rates in response to changes in the local environment may provide new information about intracellular processes. The experiments reported here demonstrate the viability of controlled single spin probes for nanomagnetometry in biological systems, opening up a host of new possibilities for quantum-based imaging in the life sciences.

Coherent coupling between single quantum objects is at the heart of modern quantum physics. When coupling is strong enough to prevail over decoherence, it can be used for the engineering of correlated quantum states. Especially for solid-

The exploitation of emerging quantum technologies requires efficient fabrication of key building blocks. Sources of single photons are extremely important across many applications as they can serve as vectors for quantum information-thereby allowing long-range (perhaps even global-scale) quantum states to be made and manipulated for tasks such as quantum communication or distributed quantum computation. At the single-emitter level, quantum sources also afford new possibilities in terms of nanoscopy and bio-marking. Color centers in diamond are prominent candidates to generate and manipulate quantum states of light, as they are a photostable solid-state source of single photons at room temperature. In this review, we discuss the state of the art of diamond-based single-photon emitters and highlight their fabrication methodologies. We present the experimental techniques used to characterize the quantum emitters and discuss their photophysical properties. We outline a number of applications including quantum key distribution, bio-marking and sub-diffraction imaging, where diamond-based single emitters are playing a crucial role. We conclude with a discussion of the main challenges and perspectives for employing diamond emitters in quantum information processing.

No abstract

The negatively charged nitrogen-vacancy (NV-) center in diamond has realized new frontiers in quantum technology. Here, the optical and spin resonances of the NV- center are observed under hydrostatic pressures up to 60 GPa. Our results motivate powerful new techniques to measure pressure and image high-pressure magnetic and electric phenomena. Additionally, molecular orbital analysis and semiclassical calculations provide insight into the effects of compression on the electronic orbitals of the NV- center.

Lifetime limited optical excitation lines of single nitrogen vacancy (NV) defect centers in diamond have been observed at liquid helium temperature. They display unprecedented spectral stability over many seconds and excitation cycles. Spectral tuning of the spin selective optical resonances was performed via the application of an external electric field (i.e. the Stark shift). A rich variety of Stark shifts were observed including linear as well as quadratic components. The ability to tune the excitation lines of single NV centers has potential applications in quantum information processing. 1Coupling between light and single spins in solids has attracted widespread attention particularly for applications in quantum computing and quantum communications 1 . The nitrogen-vacancy defect (NV) optical center in diamond is a particularly attractive solid state system for such applications. Its strong optical transition allows photoluminescence-based detection of single defect centers 2 . The potential of the NV center as a single photon source has been well recognized over the past few years 3,4 . Furthermore, because of its paramagnetic spin ground state, there are applications for quantum memory and quantum repeater systems 5 .In particular the long spin decoherence time (0.35ms), optical control of spin states 6-8 and the robustness of the spin coherence have enabled the demonstration of basic building block for quantum computing even at room temperature 9 .Recently it was demonstrated that the permanent magnetic dipole moment of the NV center can be exploited to couple defects for a separation distance of a few nm. Whilst this demonstrates the capability for the generation of correlated quantum states in defect center clusters, coupling based on this technique will be difficult to scale to many qubit systems.Other coupling schemes have recently been proposed which use instead their optical transition dipole moments and in some cases envisage coupling of the NV center to cavities. At the core of many such schemes is the underlying assumption that the optical transition can be tuned in resonance either with another NV center or with a cavity via an external applied field. Therefore, the ability to tune the frequency of spin-selective optical transitions of single NV centers is of crucial importance for any scalable architecture based on diamond NV centers.Externally controlled magnetic and electric fields are among the most prominent parameters that can be used for such control. Electric fields in particular allow for wide tuning of eigenstates. The electric field induced shift of the optical resonance lines has been observed for single atoms, ions in the gas phase 10 and single molecules 11 and quantum dots 12, 14 in the solid state. By contrast, for color centers in diamond, only a few bulk studies on electric field induced spectral line shifts have been carried out 15 . Usually these studies are difficult because the magnitude of the Stark effect is of the order of the inhomogeneous linewidth. Moreover, ...

The optimization of diamond films as valuable engineering materials for a wide variety of applications has required the development of robust methods for their characterization. Of the many methods used, Raman microscopy is perhaps the most valuable because it provides readily distinguishable signatures of each of the different forms of carbon (e.g. diamond, graphite, buckyballs). In addition it is non-destructive, requires little or no specimen preparation, is performed in air and can produce spatially resolved maps of the different forms of carbon within a specimen. This article begins by reviewing the strengths (and some of the pitfalls) of the Raman technique for the analysis of diamond and diamond films and surveys some of the latest developments (for example, surface-enhanced Raman and ultraviolet Raman spectroscopy) which hold the promise of providing a more profound understanding of the outstanding properties of these materials. The remainder of the article is devoted to the uses of Raman spectroscopy in diamond science and technology. Topics covered include using Raman spectroscopy to assess stress, crystalline perfection, phase purity, crystallite size, point defects and doping in diamond and diamond films.

No abstract