Single NV Research Articles

Optimal frequency measurements with quantum probes

Precise frequency measurements are important in applications ranging from navigation and imaging to computation and communication. Here we outline the optimal quantum strategies for frequency discrimination and estimation in the context of quantum spectroscopy, and we compare the effectiveness of different readout strategies. Using a single NV center in diamond, we implement the optimal frequency discrimination protocol to discriminate two frequencies separated by 2 kHz with a single 44 μs measurement, a factor of ten below the Fourier limit. For frequency estimation, we achieve a frequency sensitivity of 1.6 µHz/Hz2 for a 1.7 µT amplitude signal, which is within a factor of 2 from the quantum limit. Our results are foundational for discrimination and estimation problems in nanoscale nuclear magnetic resonance spectroscopy.

Epoxy oxidized diamond (111)-(2 × 1) surface for nitrogen-vacancy based quantum sensors

Surface functionalization of diamonds is an important topic for the negatively charged nitrogen-vacancy (NV−) center based quantum sensors. We investigate the electronic properties of oxidized diamond (111) surfaces and their effects on the NV− centers using the density of functional theory. The results show that the epoxy oxidized diamond (111) surface has neither surface spin noises nor inter-bandgap states and also has a positive electron affinity (1.85 eV) with nearly 99% preferential alignment of nitrogen-vacancy, indicating the epoxy oxidized (111) surface could be a perfect host of the NV− centers. Additionally, we make further examinations by placing an NV− center ∼1 nm from the epoxy oxidized (111) surface. The results indicate that the epoxy oxidized (111) surface has no obvious effects on the defect levels and optical transitions of the single NV− center. To the best our knowledge, the epoxy oxidized (111)-(2 × 1) surface may be the first diamond surface that not only theoretically satisfies the electronic requirements of shallow NV− centers but can also be fabricated through the oxidization process. Therefore, the epoxy oxidized diamond (111)-(2 × 1) surface is the most promising candidate to be applied in NV-based quantum sensors.

Ultra-sensitive hybrid diamond nanothermometer.

Nitrogen-vacancy (NV) centers in diamond are promising quantum sensors because of their long spin coherence time under ambient conditions. However, their spin resonances are relatively insensitive to non-magnetic parameters such as temperature. A magnetic-nanoparticle-nanodiamond hybrid thermometer, where the temperature change is converted to the magnetic field variation near the Curie temperature, were demonstrated to have enhanced temperature sensitivity (n}{}11{rm{,,mK,,H}}{{rm{z}}^{ - 1/2}}) (Wang N, Liu G-Q and Leong W-H et al. Phys Rev X 2018; 8: 011042), but the sensitivity was limited by the large spectral broadening of ensemble spins in nanodiamonds. To overcome this limitation, here we show an improved design of a hybrid nanothermometer using a single NV center in a diamond nanopillar coupled with a single magnetic nanoparticle of copper-nickel alloy, and demonstrate a temperature sensitivity of n}{}76{rm{,,mu K,,H}}{{rm{z}}^{ - 1/2}}. This hybrid design enables detection of 2 mK temperature changes with temporal resolution of 5 ms. The ultra-sensitive nanothermometer offers a new tool to investigate thermal processes in nanoscale systems.

Optical investigation of as-grown NV centers in heavily nitrogen doped delta layers in CVD diamond

In this paper, we realize growth of the delta doped layer (3 nm thick) with high concentration of nitrogen atoms (about 1.4 × 1019 cm−3) during CVD diamond growth process. We experimentally investigate the distribution of the nitrogen inside the grown layer and formation of the NV centers during such growth. Using confocal microscopy, we analyze the spatial distribution of the NV centers and investigate the formation efficiency of the NV centers in delta doped layers. The spatial distribution is measured by two methods, using second-order correlation function and emission volume analysis, and NV center concentration is found to be 3.9 ± 0.6 and 2.7 ± 0.2 μm-2 consequently. The divergence between the methods is discussed. As-grown NV centers formation efficiency was found to be 30 times lower than in the case of uniform doped diamond growth. Nevertheless, coherence time of an electron spin for a single NV center inside the delta layer was found to be around 1 μs which is quite reasonable given the concentration of the nitrogen in the sample.

Window into NV center kinetics via repeated annealing and spatial tracking of thousands of individual NV centers

Knowledge of the nitrogen-vacancy center formation kinetics in diamond is critical to engineering sensors and quantum information devices based on this defect. Here we utilize the longitudinal tracking of single NV centers to elucidate NV defect kinetics during high-temperature annealing from 800-1100 $^\circ$C in high-purity chemical-vapor-deposition diamond. We observe three phenomena which can coexist: NV formation, NV quenching, and NV orientation changes. Of relevance to NV-based applications, a 6 to 24-fold enhancement in the NV density, in the absence of sample irradiation, is observed by annealing at 980 $^\circ$C, and NV orientation changes are observed at 1050 $^\circ$C. With respect to the fundamental understanding of defect kinetics in ultra-pure diamond, our results indicate a significant vacancy source can be activated for NV creation between 950-980 $^\circ$C and suggests that native hydrogen from NVH$_y$ complexes plays a dominant role in NV quenching, in agreement with recent {\it ab initio} calculations. Finally, the direct observation of orientation changes allows us to estimate an NV diffusion barrier of 5.1~eV.

Instabilities in nanodiamond nitrogen-vacancy centre single photon sources under prolonged pulsed excitation

Colour centres in nanodiamonds provide robust sources of fluorescence and can be used as triggered sources of single photons at room temperature. However, practical devices require stability over thousands of hours of operation, and the use of strong pulsed optical excitation, placing significant burden on the robustness of the emitters that requires bespoke testing. In this work we report the response of single NV centres in nanodiamonds of 50 nm and 100 nm diameter to accelerated lifetime testing, exciting the defects close to saturation around 1013 times to simulate the minimum operational lifetime of a practical device. For nanodiamonds 50 nm in diameter, observed changes in the fluorescence intensity and lifetime suggest a progressive size reduction as a result of the pulsed laser excitation, combined with the introduction of non-radiative centres on or near the nanodiamond surface which affect the quantum efficiency of the NV centre and ultimately lead to photobleaching of the emission. We find examples of NV centres in 100 nm nanodiamonds for which triggered single photon emission remains stable for over these accelerated lifetime tests, demonstrating their suitability for use in practical devices.

Spatially controlled fabrication of single NV centers in IIa HPHT diamond

Single NV centers in HPHT IIa diamond are fabricated by helium implantation through lithographic masks. The concentrations of created NV centers in different growth sectors of HPHT are compared quantitatively. It is shown that the purest {001} growth sector (GS) of HPHT diamond allows to create groups of single NV centers in predetermined locations. The {001} GS HPHT diamond is thus considered a good material for applications that involve single NV centers.

Experimental simulation of hybrid quantum systems and entanglement on a quantum computer

We propose the utilization of the IBM Quantum Experience quantum computing system to simulate different scenarios involving common hybrid quantum system components, the nitrogen vacancy center (NV center), and the flux qubit. We perform a series of simulation experiments and demonstrate properties of a virtual hybrid system, including its spin relaxation rate and state coherence. In correspondence with experimental investigations, we look at the scalability of such systems and show that increasing the number of coupled NV centers decreases the coherence time. We also establish the main error rate as a function of the number of control pulses in evaluating the fidelity of the four qubit virtual circuit with the simulator. Our results show that the virtual system can attain decoherence and fidelity values comparable to what has been reported for experimental investigations of similar physical hybrid systems, observing a coherence time at 0.35 s for a single NV center qubit and fidelity in the range of 0.82. This work thus establishes an effective simulation protocol to test and evaluate different technologies as a supplementary measure that complements their experimental operation.

Plasma treatments and photonic nanostructures for shallow nitrogen vacancy centers in diamond

We investigate the influence of plasma treatments, especially a 0 V-bias, potentially low damage O2 plasma as well as a biased Ar/SF6/O2 plasma on shallow, negative nitrogen vacancy (NV−) centers. We ignite and sustain our 0 V-bias plasma using purely inductive coupling. To this end, we pre-treat surfaces of high purity chemical vapor deposited single-crystal diamond (SCD). Subsequently, we create ∼10 nm deep NV− centers via implantation and annealing. Onto the annealed SCD surface, we fabricate nanopillar structures that efficiently waveguide the photoluminescence (PL) of shallow NV−. Characterizing single NV− inside these nanopillars, we find that the Ar/SF6/O2 plasma treatment quenches NV− PL even considering that the annealing and cleaning steps following ion implantation remove any surface termination. In contrast, for our 0 V-bias as well as biased O2 plasma, we observe stable NV− PL and low background fluorescence from the photonic nanostructures.

Agreement system in Chiru

Author(s): Awan, Mechek Sampar | Abstract: Chiru is a Northwestern Kuki-Chin language spoken in twelve villages in Manipur and one village in Assam, Northeast India. The language displays verb stem alternation. Person marking occurs either with prefixes or suffixes. For prefixes, there are two sets with a very slight difference: Either the first person prefixes include a vowel that copies the vowel of the following root or they include the vowel /a/. Otherwise, both sets have a second person prefix that always remains /a/, and a third person prefix that always has the copy vowel. This difference in person markers surfaces in the distinction between intransitive S marking vs. transitive A marking. The object is marked by a single prefix nV- that indexes any speech act participant.

Monodisperse Five-Nanometer-Sized Detonation Nanodiamonds Enriched in Nitrogen-Vacancy Centers.

Nanodiamonds containing negatively charged nitrogen-vacancy (NV-) centers are versatile nanosensors thanks to their optical and spin properties. While currently most fluorescent nanodiamonds in use have at least a size of a few tens of nanometers, the challenge lies in engineering the smallest nanodiamonds containing a single NV- defect. Such a tiny nanocrystal with a single NV- center is an "optical spin label" for biomolecules, which can be detected in a fluorescence microscope. In this paper, we address two key issues toward this goal using detonation nanodiamonds (DNDs) of 4-5 nm in size. The DND samples are treated first with electron irradiation to create more vacancies. With the aid of electron paramagnetic resonance (EPR) spectroscopy, we confirm a steady increase of negatively charged NV- centers with higher fluence. This leads to a 4 times higher concentration in NV- defects after irradiation with 2 MeV electrons at a fluence of 5 × 1018 e-/cm2. Interestingly, we observe that the annealing of DND does not increase the number of NV- centers, which is in contrast to bulk diamond and larger nanodiamonds. Since DNDs are strongly aggregated after the irradiation process, we apply a boiling acid treatment as a second step to fabricate monodisperse DNDs enriched in NV- centers. These are two important steps toward "optical spin labels" having a single-digit nanometer range size that could be used for bioimaging and nanosensing.

A Planar Scanning Probe Microscope

Scanning probe microscopy (SPM) is traditionally based on very sharp tips, where the small size of the apex is critical for resolution. This paradigm is about to shift, since a novel generation of planar probes (color centers in diamond, superconducting sensors and single electron transistors) promises to image small electric and magnetic fields with hitherto inaccessible sensitivity. To date, much effort has been put into fabricating these planar sensors on tip-like structures. This compromises performance and poses a considerable engineering challenge, which is mastered by only a few laboratories. Here we present a radically simplified, tipless, approach - a technique for scanning an extended planar sensor parallel to a planar sample at a distance of few tens of nanometers. It is based on a combination of far-field optical techniques to measure both tilt and distance between probe and sample with sub-mrad and sub-nm precision, respectively. Employing these measurements as a feedback signal, we demonstrate near-field optical imaging of plasmonic modes in silver nanowires by a single NV center. Our scheme simultaneously improves the sensor quality and enlarges the range of available sensors beyond the limitations of existing tip-based schemes.

Sensing phases of water via nitrogen-vacancy centres in diamond

Ultra-thin layers of liquids on a surface behave differently from bulk liquids due to liquid-surface interactions. Some examples are significant changes in diffusion properties and the temperature at which the liquid-solid phase transition takes place. Indeed, molecular dynamics simulations suggest that thin layers of water on a diamond surface may remain solid even well above room temperature. However, because of the small volumes that are involved, it is exceedingly difficult to examine these phenomena experimentally with current technologies. In this context, shallow NV centres promise a highly sensitive tool for the investigation of magnetic signals emanating from liquids and solids that are deposited on the surface of a diamond. Moreover, NV centres are non-invasive sensors with extraordinary performance even at room-temperature. To that end, we present here a theoretical work, complemented with numerical evidence based on bosonization techniques, that predicts the measurable signal from a single NV centre when interacting with large spin baths in different configurations. In fact, by means of continuous dynamical decoupling, the polarization exchange between a single NV centre and the hydrogen nuclear spins from the water molecules is enhanced, leading to differences in the coherent dynamics of the NV centre that are interpreted as an unambiguous trace of the molecular structure. We therefore propose single NV centres as sensors capable to resolve structural water features at the nanoscale and even sensitive to phase transitions.

Coherent control of solid state nuclear spin nano-ensembles

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 13C nuclear spins doped with nitrogen-vacancy centres (NV) embedded in a spin-free 12C crystal matrix. A single NV in the vicinity of the layer is used for polarization of the 13C 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 and Ramsey spectroscopy, though any NMR pulse sequence can be implemented. The results shown here present an important step towards the realization of a nuclear spin based quantum simulator.

22pWB-3 ダイヤモンド中の単一NV中心における核スピンを用いた量子情報研究(22pWB 領域12シンポジウム:単一分子分光の最前線,領域12(ソフトマター物理,化学物理,生物物理))

22pWB-3 ダイヤモンド中の単一NV中心における核スピンを用いた量子情報研究(22pWB 領域12シンポジウム:単一分子分光の最前線,領域12(ソフトマター物理,化学物理,生物物理))

Nanoscale magnetic field sensing and imaging based on nitrogen-vacancy center in diamond

Magnetic field measurement and imaging with nanometer resolution is a key tool in the study of magnetism. There have been several powerful techniques such as superconducting quantum interference device, hall sensor, electron microscopy, magnetic force microscopy and spin polarized scanning tunneling microscopy. However, they either have poor sensitivity or resolution, or need severe environment of cryogenic temperature or vacuum. The nitrogen-vacancy color center (NV center) in diamond, serving as a quantum magnetic sensor, has great advantages such as long decoherence time, atomic size, and ambient working conditions. The NV center consists of a substitutional nitrogen atom and an adjacent vacancy in diamond. Its electronic structure of ground state is a spin triplet. The spin state can be initialized to mS=0 state and read out by laser pulse, and coherently manipulated by microwave pulse. It is sensitive to the magnetic field by measuring the magnetic Zeeman splitting or quantum phase in quantum interferometer strategies. By using dynamical decoupling sequence to prolong the decoherence time, the sensitivities approach to nano tesla for a single NV center and pico tesla for the NV center ensemble, respectively. As a sensor with an atomic size, it reaches single-nuclear-spin sensitivity and sub-nanometer spatial resolution. Combining with scanning microscopy technology, it can accomplish high-sensitivity and high-resolution magnetic field imaging so that the stray field can be reconstructed quantitatively. The magnetic field is calculated from the two resonant frequencies by solving the Hamiltonian of NV center in order to obtain the value of stray field. Recently, this novel magnetic imaging technique has revealed the magnetization structures of many important objects in magnetism research. The polarity and chirality of magnetic vortex core are determined by imaging its stray field; laser induced domain wall hopping is observed quantitatively with a nanoscale resolution; non-linear antimagnetic order is imaged in real space by NV center. It was recently reported that magnetization of the magnetic skyrmion is imaged by NV center. The magnetization distribution is reconstructed from stray field imaging. With the topological number limited to one, the Nel type magnetization is uniquely determined. These results show that the magnetic imaging method has great advantages to resolve the emerging magnetic structure materials. The magnetic imaging technology based on the NV center will potentially become an important method to study magnetic materials under continuous development.

Single bright NV centers in aggregates of detonation nanodiamonds

In this paper, we experimentally investigate optical and spin properties of NV centers in aggregates of detonation nanodiamonds. We show that despite the small size of nanodiamonds forming the aggregate, the NV centers in these aggregates exhibit spin properties comparable to similar size nanodiamonds grown by other methods, but with brightness enhanced by a factor of 2.

Resonance fluorescence and quantum interference of a single NV center

The detection of a single nitrogen-vacancy center in diamond has attracted much interest, since it is expected to lead to innovative applications in various domains of quantum information, including quantum metrology, information processing and communications, as well as in various nanotechnologies, such as biological and subdiffraction limit imaging, and tests of entanglement in quantum mechanics. We propose a novel scheme of a single NV center coupled with a multi-mode superconducting microwave cavity driven by coherent fields in squeezed vacuum. We numerically investigate the spectra in-phase quadrature and out-of-phase quadrature for different driving regimes with or without detunings. It shows that the maximum squeezing can be obtained for optimal Rabi fields. Moreover, with the same parameters, the maximum squeezing is greatly increased when the detunings are nonzero compared to the resonance case.

Spin-manipulated nanoscopy for single nitrogen-vacancy center localizations in nanodiamonds

Due to their exceptional optical and magnetic properties, negatively charged nitrogen-vacancy (NV−) centers in nanodiamonds (NDs) have been identified as an indispensable tool for imaging, sensing and quantum bit manipulation. The investigation of the emission behaviors of single NV− centers at the nanoscale is of paramount importance and underpins their use in applications ranging from quantum computation to super-resolution imaging. Here, we report on a spin-manipulated nanoscopy method for nanoscale resolutions of the collectively blinking NV− centers confined within the diffraction-limited region. Using wide-field localization microscopy combined with nanoscale spin manipulation and the assistance of a microwave source tuned to the optically detected magnetic resonance (ODMR) frequency, we discovered that two collectively blinking NV− centers can be resolved. Furthermore, when the collective emitters possess the same ground state spin transition frequency, the proposed method allows the resolving of each single NV− center via an external magnetic field used to split the resonant dips. In spin manipulation, the three-level blinking dynamics provide the means to resolve two NV− centers separated by distances of 23 nm. The method presented here offers a new platform for studying and imaging spin-related quantum interactions at the nanoscale with super-resolution techniques.

Effect of a radical exposure nitridation surface on the charge stability of shallow nitrogen-vacancy centers in diamond

A nitridation process of a diamond surface with nitrogen radical exposure far from the radio-frequency plasma for the stabilization of a negatively charged nitrogen-vacancy (NV−) centers near the surface is presented. At a nitrogen coverage of as high as 0.9 monolayers, high average Rabi contrasts of 0.40 ± 0.06 and 0.46 ± 0.03 have been obtained for single NV− centers formed by shallow nitrogen implantation with acceleration voltages of 1 and 2 keV, respectively. This indicates that nitrogen termination by a radical exposure process produces an electric charge state suitable for single NV− centers near the surface compared with the states obtained for alternatively terminated surfaces.