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Confocal fluorescence images on a diamond sample with low defect center concentration. The fluorescence intensity is decoded in gray scale. Points of high intensity are indicated by white color. a-c: Excitation with 1.945 eV optical excitation alone. d-f: Excitation with 1.945 and 2.54 eV deshelving. ac and d-f do not correspond to the same areas within the sample. Images a and d are recorded at T300 K, images b and e at 200 K, and c, f at T60 K.
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Individual nitrogen-vacancy defect centers have been investigated by low-temperature confocal microscopy and fluorescence excitation spectroscopy. At temperatures below 90 K the fluorescence intensity of individual centers drastically diminishes because of the population of a metastable singlet state in near resonance with the optically excited sta...
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... at cryostate windows and filters and the limited quantum efficiency of the detector result in an overall detection efficiency of 0.46% for the fluorescence of indi- vidual N-V defect centers. Figures 1a-1c show confocal fluorescence images of a diamond sample with low N-V center concentration in a tem- perature range of 300 to 65 K. The fluorescence is excited via the zero-phonon line of the lowest electronic transition at 1.945 eV. ...
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... of 0.46% for the fluorescence of indi- vidual N-V defect centers. Figures 1a-1c show confocal fluorescence images of a diamond sample with low N-V center concentration in a tem- perature range of 300 to 65 K. The fluorescence is excited via the zero-phonon line of the lowest electronic transition at 1.945 eV. Individual spots visible in Fig. 1a are attributed to the fluorescence of single N-V centers. 5 A first, unex- pected finding is that the fluorescence intensity of single cen- ters decrease beyond a detectable level below a temperature of 80 K see Figs. 1b and 1c. Based on the currently known photophysical parameters of the center and consider- ing that the absorption ...
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... fluorescence is excited via the zero-phonon line of the lowest electronic transition at 1.945 eV. Individual spots visible in Fig. 1a are attributed to the fluorescence of single N-V centers. 5 A first, unex- pected finding is that the fluorescence intensity of single cen- ters decrease beyond a detectable level below a temperature of 80 K see Figs. 1b and 1c. Based on the currently known photophysical parameters of the center and consider- ing that the absorption cross section should increase upon a reduction in temperature one would not expect any such change. However, the saturated fluorescence intensity R is found to decreases from 200 to 4 K by more than one order of magnitude, as ...
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... 1D-1E repre- sents a series of images equivalent to Figs. 1A-1C, dem- onstrating the deshelving of individual centers at low T. Fig- ures 1d and 1e have been recorded with simultaneous excitation at 1.945 and 2.56 eV. It should be noted that ex- citation at 2.54 eV alone does not result in a detectable fluo- rescence from individual centers. ...
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... Nitrogen creates various paramagnetic centers in a diamond and exists as individual atoms and nitrogen clusters. Recently, a great interest has been inspired by the studies of nitrogen vacancy centers (NV − defects) in a diamond, for which the magnetic resonance on single defects was successfully observed at room temperature [1][2][3][4]. The NV − center [5], also known as W15 in the notation of electron paramagnetic resonance (EPR) spectroscopy [6], is a complex consisting of a nitrogen atom substituting carbon in the diamond lattice and a vacancy at a neighboring site. ...
... Optical excitation causes preferential population of the M S = 0 sublevel. This makes it possible to study them using ODMR [1][2][3][4]7]. ...
Magnetic resonance methods for express analysis and control of diamond wafers with NV⁻ centers for quantum technologies were developed. The scanning NV⁻-based ODMR spectrometer was built to analyze NV⁻ local concentration, coherent properties, stress/strain, nitrogen content, electron-nuclear interactions in diamond wafers for quantum technologies. As an example, a 3D image of the ODMR and PL maps was presented for a non-uniform distribution of NV⁻ centers in a diamond wafer, which had several growth zones with significantly different concentrations of nitrogen. The local stress/strain map was obtained by measuring the splitting of the ODMR line in zero magnetic field at room temperature. The double ODMR line is a consequence of the stress-induced splitting of the doublet with projections MS = + 1 and MS = − 1 in the ground triplet state of the NV⁻ center. Local concentration of nitrogen donors (in EPR literature it is designated as N or P1 centers) was estimated from the ratio of the intensity of satellites caused by interaction with nitrogen donors and the central line of ODMR. The central line has a 2E split into two overlapping lines, the intensity of one of the lines is selected. The spectrometer is also designed to perform pulsed measurements of Rabi oscillations, spin–lattice and spin–spin relaxation times at wafer points isolated by focused laser excitation. A new option for using a spectrometer was introduced for measuring the ODMR of NV⁻ centers in a linearly polarized light, which allowed to distinguish PL for centers of a certain orientation and suppress the PL from others.
... In this defect, the crystal field splitting lifts the ground state spin degeneracy and provides the required unique quantum degree of freedom to form an addressable two-level system [7][8][9][10] . In addition, NV centers are single photon sources [11][12][13] and therefore constitute excellent building blocks for future quantum photonic circuits. However, a key prerequisite for such applications is the ability to position defects deterministically. ...
Single spin-defects in 2D transition-metal dichalcogenides are natural spin-photon interfaces for quantum applications. Here wereport high-field magneto-photoluminescence spectroscopy from three emission lines (Q1, Q2, and Q*) of He-ion induced sulfurvacancies in monolayer MoS2. Analysis of the asymmetric PL lineshapes in combination with the diamagnetic shift of Q1 and Q2yields a consistent picture of localized emitters with a wave function extent of ~3.5 nm. The distinct valley-Zeeman splitting in out-of-planeB-fields and the brightening of dark states through in-planeB-fields necessitates spin-valley selectivity of the defect statesand lifted spin-degeneracy at zerofield. Comparing our results to ab initio calculations identifies the nature of Q1 and Q2 andsuggests that Q* is the emission from a chemically functionalized defect. Analysis of the optical degree of circular polarizationreveals that the Fermi level is a parameter that enables the tunability of the emitter. These results show that defects in 2Dsemiconductors may be utilized for quantum technologies.
... The first detection of electron paramagnetic resonance (EPR) from a single NV defect was reported in 1997 by Gruber et al. [14]. Although ensembles of NV centers have been observed prior to 1997, this initial detection of single centers triggered an intense research effort in the context of diamond-based quantum technologies, and the NV center became a popular platform to develop various quantum manipulation protocols [15,16,17,18]. ...
The nitrogen-vacancy (NV) center in diamond is a promising quantum platform for magnetometry applications exhibiting optical readout of minute energy shifts in its spin sub-levels even at room temperature. In particular, NV-ensembles in bulk diamonds are favored for a considerably improved signal-to-noise ratio and sensitivity. Key material requirements for general NV-ensemble-based applications are a high NV⁻ concentration, a long spin coherence time, and a stable charge state. Additionally, for specific applications that require large detection volumes, for example, the multi-pass readout or cavity coupling, a low optical loss in the material is also an essential need, calling for a low diamond absorption and a low birefringence. These requirements, however, are interdependent and can be difficult to optimize during diamond growth and subsequent NV creation. Therefore, better understanding the correlation between these material properties and finding their balances are crucial for improved sensitivity from the material side.
Chemical vapor deposition (CVD) diamonds typically exhibit NV concentrations below 10 parts per million (ppm), but often show a high homogeneity in the NV distribution. Moreover, the nitrogen incorporation during the CVD synthesis can be precisely controlled. With these advantages, the CVD diamond attracts more and more interest in NV research. In contrast, high-pressure high-temperature (HPHT) synthesis with higher NV concentrations (up to dozens of ppm) is also of great interest. However, its inhomogeneity in the nitrogen distribution and less controllability of the nitrogen concentration raise challenges when applying it to the sensing systems.
In this thesis, the author investigates optical, NV and spin properties of diamonds, specifically for CVD diamonds with a wide variety of nitrogen densities but also in comparison with HPHT diamonds. This thesis studies the optimal process in the creation of NV centers and the link to optical properties. The author develops novel optical methods in this thesis to determine the defect concentrations, which are more widely accessible and easier to implement than the conventional methods. Additionally, the author establishes various characterization protocols to systematically study NV and diamond properties. Based on these methods, CVD diamond series with varied nitrogen flow over 4 orders of magnitude are investigated, to understand the incorporation of single substitutional nitrogen atoms (P1 centers) and NV creation during the growth. For a fixed nitrogen concentration, varied electron-irradiation fluences are investigated and optimized for two different accelerated electron energies. Defect transformations during the irradiation and annealing treatments are studied via optical characterizations. The author points out that with increasing fluences a turning point exists, above which mainly the undesirable NV charge state (NV⁰) is being created, indicating an optimum that balances the high conversion efficiency and charge stability. A general approach is suggested by the author to determine the optimal irradiation conditions, for which an enhanced NV concentration and an optimum of NV charge states can both be satisfied. Optimizing the treatment, this thesis achieves spin-spin coherence times T₂ ranging from 45.5 to 549 μs for CVD diamonds containing 168 to 1~parts per billion (ppb) NV⁻ centers, respectively. This enables better combinations of high NV concentrations and long coherence times in bulk diamonds compared to previous works.
Diamond is an excellent host for advanced optical/photonic applications, however, doping can compromise the optical properties significantly. Therefore, the author further investigates relationships and ways of combining high NV concentrations with improved optical properties, specifically absorption and birefringence. Based on this, high temperature (HT) treatments are introduced as a promising candidate to reduce optical loss, while not conflicting with the requirement for high NV⁻ concentrations. This thesis shows a pathway to engineering properties of NV-doped CVD diamonds for improved sensitivity.
... The first work in which single NV-centers were observed was published in 1997 [11]. After the discovery of single negatively charged centers, it was possible to demonstrate the photostable generation of single photons [12,13], which allowed the use of NV-centers in the implementation of quantum optical networks, as well as for electron spin readout [14,15], which defines such an NV-center as a possible solid state spin cubit, suitable for quantum information processing and applications in quantum sensing. ...
Currently, diamonds are widely used in science and technology. However, the properties of diamonds due to their defects are not fully understood. In addition to optical methods, positron annihilation spectroscopy (PAS) can be successfully used to study defects in diamonds. Positrons are capable of detecting vacancies, and small and large clusters of vacancies induced by irradiation, by providing information about their size, concentration, and chemical environment. By mapping in the infrared (IR) range, it is possible to consider the admixture composition of the main inclusions of the whole plate. This article presents the results of a study of defects in synthetic diamond plates, one of which was irradiated by electrons. It presents data about the distribution of the defect concentration obtained by Infrared spectroscopy. PAS with a monochromatic positron beam can be used as a non-destructive technique of detecting defects (vacancy) distribution over the depth of diamond plates.
... The first work in which single NV-centers were observed was published in 1997 [11]. After the discovery of single negatively charged centers, it was possible to demonstrate the photostable generation of single photons [12,13], which allowed the use of NV-centers in the implementation of quantum optical networks, as well as for electron spin readout [14,15], which defines such an NV-center as a possible solid state spin cubit, suitable for quantum information processing and applications in quantum sensing. ...
Nowadays, diamonds are widely used in science and technology. However, the properties of diamonds due to their defects are not fully understood. In addition to optical methods, positron annihilation spectroscopy (PAS) can be successfully used to study defects in diamonds. Positrons are capable of detecting vacancies, small and large clusters of vacancies induced by irradiation, by providing information about their size, concentration, and chemical environment. By mapping in the infrared (IR) range, it is possible to consider the admixture composition of the main inclusions of the whole plate. The article presents the results of the study of defects in synthetic diamond plates, one of which was irradiated by electrons. Presents data about the distribution of the defect concentration obtained by Infrared spectroscopy. PAS with a monochromatic positron beam can be used as a non-destructive technique of detecting defects (vacancy) distribution over the depth of diamond plates.
... The ground singlet state, commonly referred to as a metastable state due to its long lifetime, ∼300 ns, decays back to the ground triplet state. Theoretical studies have predicted different values for the energy of the singlet state [7][8][9][10][11][12][13][14][15][16]. However, the energy gap between the singlet manifold and the conduction band has yet to be measured experimentally, and is the focus of this work. ...
... ious values for the energy of the singlet state, and experimental data is required in order to constrain this parameter [7][8][9][10][11][12][13][14]16]. ...
The singlet states of the negatively-charged nitrogen-vacancy centers in diamond play a key role in its optical spin control and readout. In this work, the hitherto unknown ionization energy of the singlet is measured experimentally and found to be between 1.91-2.25 eV. This is obtained by analyzing photoluminescence measurements incorporating spin control and NV charge state differentiation, along with simulations based on the nitrogen-vacancy's master equation. This work establishes a protocol for a more accurate estimate of this ionization energy, which can possibly lead to improved read-out methods.
... The NV centers in diamond is a point defect consisting of a substitutional nitrogen atom and an adjacent lattice vacancy, [70] as shown in Figure 5a. It can accept an extra electron from the environment to form the negatively charged NV − , which has been studied extensively and deeply over the past decade [71][72][73] owing to its remarkable properties in initialization, manipulation, and readout. As a solid-state single spin system working at ambient conditions, NV − plays an important role in quantum computing, quantum network, and quantum metrology. ...
With the advancement of computing power and algorithms, machine learning has been a powerful tool in numerous applications nowadays. However, the hardware limitation of classical computers and the increasing size of datasets urge the community to explore new techniques for machine learning. Quantum‐enhanced machine learning is such a rapidly growing field. It refers to quantum algorithms that are implemented in quantum computers, which can improve the computational speed of classical machine learning tasks and often promises an exponential speedup. In the past few years, the development of experimental quantum technologies leads to many experimental demonstrations of quantum‐enhanced machine learning in diverse physical systems. Here, the recent experimental progress in this field in two typical spin‐based quantum systems—nuclear magnetic resonance and nitrogen‐vacancy centers in diamond—is reviewed, and the ongoing challenges are discussed.
... In this defect, the crystal field splitting lifts the ground state spin degeneracy and provides the required unique quantum degree of freedom to form an addressable two-level system [6][7][8][9]. Additionally, NV centers are single photon sources [10][11][12] and therefore constitute excellent building blocks for future quantum photonic circuits. However, a key prerequisite for such applications is the ability to position defects deterministically. ...
Single spin defects in 2D transition-metal dichalcogenides are natural spin-photon interfaces for quantum applications. Here we report high-field magneto-photoluminescence spectroscopy from three emission lines (Q1, Q2 and Q*) of He-ion induced sulfur vacancies in monolayer $\text{MoS}_2$. Analysis of the asymmetric PL lineshapes in combination with the diamagnetic shift of Q1 and Q2 yields a consistent picture of localized emitters with a wavefunction extent of $\sim$\nm{3.5}. The distinct valley-Zeeman splitting in out-of-plane $B$-fields and the brightening of dark states through in-plane $B$-fields necessitates spin-valley selectivity of the defect states and lifted spin-degeneracy at zero field. Comparing our results to ab-initio calculations identifies the nature of Q1 and Q2 and suggests that Q* is the emission from a chemically functionalized defect. Analysis of the optical degree of circular polarization reveals that the Fermi level is a parameter that enables the tunability of the emitter. These results show that defects in 2D semiconductors may be utilized for quantum technologies.
... Both charge states of the NV color center have been identified as room temperature single photon sources [17][18][19]. This was confirmed through statistically-significant antibunching dips observed through second-order autocorrelation measurements [often abbreviated as g (2) (τ)]. ...
In this work, the lifetime of nitrogen-vacancy color centers within nanodiamonds is reduced from 550±13 ps to 297±10 ps through the implantation of xenon. Coupled-mode analysis is employed to characterize the mechanism responsible for the reduction in emission lifetime. The observed spectral lineshape is found to be consistent with a Voigt profile consisting of two Lorentzian resonant peaks at 637 nm and 811 nm that are inhomogeneously broadened by a Gaussian distribution. A convolution of the frequency-domain Lorentzian output, with linewidths less than 1 nm, from the coupled-mode system of equations with a Gaussian with standard deviation of 85 nm is performed to generate the Voigt profile. The shortened emission lifetime is found to be consistent with a coupled mode theory model incorporating coupling between nitrogen-vacancy and xenon-vacancy color centers.
... Also, in the early model 2.1. THE N V − CENTER 7 of the electronic structure of the N V − center, the existence of only one 1 A 1 singlet has often been considered [31,32]. According to the currently accepted model the 1 E state is lower than the 1 A 1 state [33]. ...
The aim of this thesis is to study the influence of the pressure on the optical transitions between multi-determinant ground state and excited states of the NV center from the first-principles.In this work, I study both the neutral NV0 and negatively charged NV- centers.Long-range interactions have a crucial effect in such defects: first, elastic deformations have a long range and need to be accounted for; second, when the defect has a charge, it is important to avoid spurious charge-charge interactions between neighboring supercells caused by the use of periodic boundary conditions. Thus, I study the atomic structure of defect with large supercells by the density functional theory (DFT).The NV center is a deep-center defect, its optical and magnetic properties are related with localized levels in the electronic band-gap. These levels are believed to be built out of the localized orbitals of dangling bonds pointing towards the vacancy, providing strongly correlated electronic states. Thus, an accurate quantum mechanical treatment is needed.DFT is a powerful approach for the calculation of the ground state properties of defects. However, the single Slater determinant nature of the DFT wave function lacks the non-dynamical correlations, that characterize such defects, and does not allow for the calculation of many-body levels. Moreover, exchange and correlation (XC) functionals used in DFT add have a limited accuracy.Therefore, in this PhD work, I first develop a combined DFT + Hubbard model technique. I study the triplet-triplet transition both with the PBE XC functional and the HSE06 one. I confirm that the use of the hybrid XC functional HSE06 improves the description of correlations beyond DFT-PBE and allows for more accurate prediction of optical transitions.An exact diagonalization (or in quantum chemistry language full Configuration Interaction calculations) of the Hubbard Hamiltonian in the many-electron basis constructed of in-gap localized levels, allows to get access to multi-determinant ground and excited states. I benchmark this technique comparing it to the recent state of the art methods.Finally, I apply the developed technique in order to study the effect of the hydrostatic pressure on NV- and NV0 centers. Among many results of my work, I discovered a very interesting effect related to the singlet-singlet transition in the NV-center under hydrostatic pressure. The results I have obtained during my PhD have never been calculated nor observed experimentally. In order to validate the theoretical model, I have compared our results with the measurements that have been obtained by our experimental collaborators for the optical transition in the NV- and NV0. Last but not least, the effect of the electron-phonon interaction was discussed.As a perspective, I developed a new code that can be applied to study other defect systems of interest in the quantum technologies.
