Vacancy In Diamond Research Articles

Uniform microwave field formation for control of ensembles of negatively charged nitrogen vacancy in diamond.

The homogeneity of the microwave magnetic field is essential in controlling a large volume of ensemble spins, for example, in the case of sensitive magnetometry with nitrogen-vacancy (NV) centers in diamond. This is particularly important for pulsed measurement, where the fidelity of control pulses plays a crucial role in its sensitivity. So far, several magnetic field-forming systems have been proposed, but no detailed comparison has been made. Here, we numerically study the homogeneity of five different systems, including a planar antenna, a dielectric resonator, a cylindrical inductor, a barrel-shaped coil, and a nested barrel-shaped coil. The results of the simulation allowed us to optimize the design parameters of the barrel-shaped field-forming system, which led to significantly improved magnetic field uniformity. To measure this effect, we experimentally compared the homogeneity of a field-forming system having a barrel shape with that of a planar field-forming system by measuring Rabi oscillations of an ensemble of NV centers with them. Significant improvements in inhomogeneity were confirmed in the barrel-shaped coil.

Realization of robust quantum noise characterization in the presence of coherent errors

Complex quantum systems and their various applications are susceptible to noise of coherent and incoherent nature. Characterization of noise and its sources is an open, key challenge in quantum technology applications, especially in terms of distinguishing between inherent incoherent noise and systematic coherent errors. In this paper, we study a scheme of repeated sequential measurements that enables the characterization of incoherent errors by reducing the effects of coherent errors. We demonstrate this approach using a coherently controlled nitrogen vacancy in diamond, coupled to both a natural nuclear spin bath (non-Markovian) and to experimentally controlled relaxation through an optical pumping process (nearly Markovian). Our results show mitigation of coherent errors both for Markovian and non-Markovian incoherent noise profiles. We apply this scheme to the estimation of the dephasing time (T2*) due to incoherent noise. We observe an improved robustness against coherent errors in the estimation of dephasing time (T2*) compared to the standard (Ramsey) measurement.

Fast optoelectronic charge state conversion of silicon vacancies in diamond.

Group IV vacancy color centers in diamond are promising spin-photon interfaces with strong potential for applications in photonic quantum technologies. Reliable methods for controlling and stabilizing their charge state are urgently needed for scaling to multiqubit devices. Here, we manipulate the charge state of silicon vacancy (SiV) ensembles by combining luminescence and photocurrent spectroscopy. We controllably convert the charge state between the optically active SiV- and dark SiV2- with megahertz rates and >90% contrast by judiciously choosing the local potential applied to in-plane surface electrodes and the laser excitation wavelength. We observe intense SiV- photoluminescence under hole capture, measure the intrinsic conversion time from the dark SiV2- to the bright SiV- to be 36.4(67) ms, and demonstrate how it can be enhanced by a factor of 105 via optical pumping. Moreover, we obtain previously unknown information on the defects that contribute to photoconductivity, indicating the presence of substitutional nitrogen and divacancies.

Local Excitations of a Charged Nitrogen Vacancy in Diamond with Multireference Density Matrix Embedding Theory

We investigate the negatively charged nitrogen-vacancy center in diamond using periodic density matrix embedding theory (pDMET). To describe the strongly correlated excited states of this system, the complete active space self-consistent field (CASSCF) followed by n-electron valence state second-order perturbation theory (NEVPT2) was used as the impurity solver. Since the NEVPT2-DMET energies show a linear dependence on the inverse of the size of the embedding subspace, we performed an extrapolation of the excitation energies to the nonembedding limit using a linear regression. The extrapolated NEVPT2-DMET first triplet-triplet excitation energy is 2.31 eV and that for the optically inactive singlet-singlet transition is 1.02 eV, both in agreement with the experimentally observed vertical excitation energies of ∼2.18 eV and ∼1.26 eV, respectively. This is the first application of pDMET to a charged periodic system and the first investigation of the NV- defect using NEVPT2 for periodic supercell models.

Three-dimensional fourier imaging of thousands of individual solid-state quantum bits – a tool for spin-based quantum technology

Nitrogen vacancies in diamond (NVs) are frequently considered as possible candidates to constitute the building blocks of spin-based quantum computers. The main caveats to this approach are the lack of a reliable process to accurately place many NVs in close proximity to each other (∼10–20 nm) to enable an adequate spin-spin interaction; and the inability to read out and selectively manipulate the quantum states of many such closely spaced NVs. A possible approach to overcome these issues includes the following: (i) making use of a diamond dense with NVs in random (‘as-produced’) 3D positions; (ii) mapping out their individual locations at high spatial resolution (in 3D); (iii) employing techniques for selective spin manipulation based on the mapped 3D locations of the NVs; and (iv) making use of imaging techniques to read out the quantum state of the NVs. Within this grand vision, we present here a tool that can support this scheme—namely, an approach to the efficient high accuracy 3D mapping of many thousands of individual NVs in a diamond via magnetic resonance imaging (MRI). In the present work, the NVs’ spacings and the corresponding imaging resolution are in the submicron-scale, but the same approach can be scaled down to support a resolution lower than 10 nm in diamonds with dense NVs, as is required for practical quantum computing applications.

ENGINEERING GEOMETRIC PHASE AND CORRELATION DYNAMICS OF NITROGEN VACANCIES IN DIAMOND INTERACTING WITH TWO NANOCAVITIES

In this paper, we study the interaction of Nitrogen Vacancies in Diamond (NVD) with quantized cavity field. The system is explored analytically and the effect of the system parameters is analyzed. The stability of a quantum system with influencing factors is investigated using the Mandal Parameter. The generated correlation between the NVD and the quantized cavity field is quantified using the negativity. This study also investigates geometric phase and its dependence on the system parameters. The results show that this system holds great potential applications in quantum computation and quantum memory. Additionally, the features of the system can be controlled by the system parameters.

Photoluminescence and First-principle Calculations of the Single Vacancy in Diamond

The isolated single vacancy is one of the most common defects in diamond, while it is of considerable interest and importance that significantly influences the optical properties of diamond. Although a number of literature publications about the electron structure and density states of single vacancy in diamond from the density functional theory (DFT) calculations, these results are very difficult to be identified from the perspective of experiments. In this paper, the low-temperature photoluminescence (PL) technology was employed to study the emission properties of single vacancy in diamond, and then the photoionization energy, migration energy and vibrionic structure obtained from PL experiments were compared with these obtained from the first-principle calculations. Results showed that the calculation results agreed well with the PL results for the neutral vacancy while differed for the negatively charged vacancy, indicating that for ultrapure diamond, the vacancy mainly existed in form of the neutral rather than the negatively charged.

Structural stability and optical properties of Ni complex defects in diamond

Structural stability of defect complexes composed of several Ni atoms and C vacancies in diamond are studied by first-principles calculations. Results show that Ni atoms prefer accumulating with C vacancies, forming Ni-Ni complex defects, rather than to be isolated as separated point defects. Focusing on complex defects consisting of one or two Ni, the electronic structures associated with the defects near the band gap are analyzed, and their optical properties including zero-phonon line energies are discussed by comparing with experimental results.

Fast, semianalytical approach to obtain the stray magnetic field above a magnetic skyrmion

We present a fast, matrix-based semianalytical method to calculate the stray magnetic field and its derivative above spin textures with cylindrical symmetry. A magnetostatic Green's function approach is used to obtain accurate fields and magnetic forces, which are confirmed using micromagnetic simulations. The developed method can be used to quickly analyze and fit experimental measurements of the stray magnetic field (measured, for example, via nitrogen vacancies in diamond) or magnetic forces (measured via magnetic force microscopy) above a thin film or patterned element. Calculations for magnetic skyrmions show that these techniques have the potential to distinguish between Bloch and N\'eel walls for skyrmions in single-layer as well as in multilayer thin films where the wall structure evolves with depth.

The calculated energies and charge and spin distributions of the excited GR1 state in diamond.

This paper reports the energies and charge and spin distributions of both the vertically excited and fully relaxed GR1 states of the neutral singlet vacancy in diamond obtained from direct Δ-SCF calculations used previously to describe the low-lying excited states in AFII NiO and α-Al2O3. The calculations are based on the B3LYP functional in its standard form, with a C basis set that is identical to that which was used previously in numerous calculations of the ground state properties of defective diamond. Both the vertically excited and thermally relaxed GR1 states are predicted to be excitonic and insulating, with extensive re-distribution of charge and spin density and back-donation to the donor site. The present calculations suggest that the triplet state makes no contribution to the GR1 excitation. The predicted energy of the zero phonon line (1.57eV) compares with the observed value of 1.67eV, which also suggests that the GR1 state is neutral. The bandgaps lead to an estimate of the next higher (GR2) excited state energy, which is close to that found in the observed spectra. Similar calculations are used to predict the energies of the higher gap states at (5.0-5.5) eV, including the bulk value of 7.3eV, which compares with the experimental value of (7.3-7.4) eV. An explanation is suggested as to why only the GR1 luminescence is observed. This paper also suggests an alternative channel for the recovery of the ground state in photoluminescence studies.

Luminescence of negatively charged single vacancies in diamond: ND1 center

Strong photoluminescence (PL) of ND1 radiation center with zero-phonon line (ZPL) at 393.5 nm has been excited in irradiated diamonds with a laser working at a wavelength of 355 nm. Emission of the ND1 center consists of ZPL and vibrational replicas related to quasilocal vibrations of an energy 76 meV. PL and absorption spectra of ND1 center exhibit very close mirror symmetry. The energies of the quasilocal vibrations are the same in luminescence and absorption. The interaction with the lattice phonons at the ND1 center is very weak. In luminescence of the irradiated diamonds, ND1 center behaves like one related to simple primary radiation defects in negative charge state. PL of the ND1 center is stimulated by nitrogen donors and suppressed by boron acceptors. It is assumed that the luminescence of the ND1 center is effectively excited only in the spectral range of its intrinsic absorption from 340 to 390 nm.

Excited States of Crystalline Point Defects with Multireference Density Matrix Embedding Theory

Accurate and affordable methods to characterize the electronic structure of solids are important for targeted materials design. Embedding-based methods provide an appealing balance in the trade-off between cost and accuracy─particularly when studying localized phenomena. Here, we use the density matrix embedding theory (DMET) algorithm to study the electronic excitations in solid-state defects with a restricted open-shell Hartree-Fock (ROHF) bath and multireference impurity solvers, specifically, complete active space self-consistent field (CASSCF) and n-electron valence state second-order perturbation theory (NEVPT2). We apply the method to investigate the electronic excitations in an oxygen vacancy (OV) on a MgO(100) surface and find absolute deviations within 0.05 eV between DMET using the CASSCF/NEVPT2 solver, denoted as CAS-DMET/NEVPT2-DMET, and the nonembedded CASSCF/NEVPT2 approach. Next, we establish the practicality of DMET by extending it to larger supercells for the OV defect and a neutral silicon vacancy in diamond where the use of nonembedded CASSCF/NEVPT2 is extremely expensive.

Selection rules in electron magnetic resonance (EMR) spectroscopy and related techniques: Fundamentals and applications to modern case systems

Allowed transitions observed using electron magnetic resonance (EMR) in transition metal (3dN or 4fN) complexes may be predicted by the selection rules. Non-standard selection rules justified by mixing of wavefunctions emerge for nominally forbidden transitions. We present tutorial guide on selection rules in EMR, optical, and inelastic neutron scattering spectroscopy. This includes basic concepts in quantum mechanics and group theory underlying derivations of selection rules and useful rules for nonzero matrix elements. These rules provide crucial information for practitioners. Survey of usage of selection rules in EMR and related studies of novel systems in emerging areas is provided at an introductory level. Applications to modern case systems include: parallel field EMR excitations for integer spin vs half-integer spin ions, nitrogen vacancies in diamond, Haldane gap systems, exchange coupled systems and molecular nanomagnets, and magnetic adatoms on surfaces. Various misconceptions concerning crucial notions, which constitute terminological confusion, have been clarified.

Effect of radiation damage on the quantum optical properties of nitrogen vacancies in diamond

Single crystal diamond (<5 ppm nitrogen) containing native NV centers with coherence time of 150 μs was irradiated with 2 MeV alpha particles, with doses ranging from 1012 ion/cm2 to 1015 ion/cm2. The effect of ion damage on the coherence time of NV centers was studied using optically detected magnetic resonance and supplemented by fluorescence and Raman microscopy. A cross-sectional geometry was employed so that the NV coherence time could be measured as a function of increasing defect concentration along the ion track. Surprisingly, although the ODMR contrast was found to decrease with increasing ion induced vacancy concentration, the measured decoherence time remained undiminished at 150us despite the estimated vacancy concentration reaching a value of 40 ppm at the end of range. These results suggest that ion induced damage in the form of an increase in vacancy concentration does not necessarily result in a significant increase in the density of the background spin bath.

Spin coherence as a function of depth for high-density ensembles of silicon vacancies in proton-irradiated 4H–SiC

Defects in wide-band-gap semiconductors provide a pathway for applications in quantum information and sensing in solid state materials. The silicon vacancy in silicon carbide has recently emerged as a new candidate for optically controlled spin qubits with significant material benefits over nitrogen vacancies in diamond. In this work, we present a study of the coherence of silicon vacancies generated via proton irradiation as a function of implantation depth. We show clear evidence of dephasing interactions between the silicon vacancies and the spin environment of the bulk crystal. These results will inform further routes toward fabrication of scalable silicon carbide devices and studies of spin interactions in high-density ensembles of defects.

Reaction: Molecular Spins as Qubits

Floriana Tuna is a Leverhulme Trust Senior Research Fellow at the University of Manchester (UoM). She holds MSc and PhD degrees in chemistry from the University of Bucharest (1989) and National Academy of Romania (1997), respectively. She worked as a visiting DAAD fellow at the University of Heidelberg (Germany), a CNRS postdoctoral fellow at ICMCB Bordeaux (France), and a Marie Curie fellow at the University of Warwick (UK) before joining UoM in 2003. She received the Romanian Academy “Ilie Murgulescu” Prize for excellence in research in 2005 and has published over 300 high-impact papers. Her major interests are in coordination chemistry, molecular magnetism, and quantum information science.

Physical mechanisms for the optical properties of the femtosecond-laser-treated black diamond

Vacancies in diamond can introduce defect bands in the band gap of diamond and lead to the sub-band gap absorption in the visible and infrared regions. At sufficiently high concentrations of vacancy, the defect bands overlap each other to form a single partially filled intermediate band (IB) in the band gap and the sub-band gap absorption in the infrared region is especially strong. Along with the decreasing of the vacancy concentrations, the IB splits into two separate bands and the sub-band gap absorption decreases sharply. The computed results are important for thoroughly understanding of the optical properties of black diamond.

Electronic structure of the neutral silicon-vacancy center in diamond

The neutrally-charged silicon vacancy in diamond is a promising system for quantum technologies that combines high-efficiency, broadband optical spin polarization with long spin lifetimes (T2 ~ 1 ms at 4 K) and up to 90% of optical emission into its 946 nm zero-phonon line. However, the electronic structure of SiV0 is poorly understood, making further exploitation difficult. Performing photoluminescence spectroscopy of SiV0 under uniaxial stress, we find the previous excited electronic structure of a single 3A1u state is incorrect, and identify instead a coupled 3Eu - 3A2u system, the lower state of which has forbidden optical emission at zero stress and so efficiently decreases the total emission of the defect: we propose a solution employing finite strain to form the basis of a spin-photon interface. Isotopic enrichment definitively assigns the 976 nm transition associated with the defect to a local mode of the silicon atom.

Scaling up solid-state quantum photonics.

Radiative coupling creates an entangled state between two silicon vacancies in diamond

Detection of nanowatt microwave radiation by the photoluminescence of an ensemble of negatively charged nitrogen vacancies in diamond

We report on detecting continuous 60-GHz microwave radiation with powers in the nanowatt range by the photoluminescence of an ensemble of negatively charged nitrogen vacancy (NV−) centers in diamond at room temperature. The high contrast of the optically detected magnetic resonance and the efficient photon collection yield a magnetic field sensitivity of 86 nT/Hz for continuous-wave laser excitation with a photon energy of 2.33 eV and a power density of 93 W/cm2. The efficiency of the microwave-power-to-magnetic-field conversion amounts to 0.54 mT/W. The microwave excitation also enhances the degree of the linear polarization of NV− photoluminescence at magnetic resonance conditions, and for linearly co-polarized NV− photoluminescence and laser light, the magnetic field sensitivity is improved by about 7%.