Nitrogen-vacancy Defect In Diamond Research Articles

Experimental signature of initial quantum coherence on entropy production

We report on the experimental quantification of the contribution to non-equilibrium entropy production stemming from the quantum coherence content in the initial state of a qubit exposed to both coherent driving and dissipation. Our experimental demonstration builds on the exquisite experimental control of the spin state of a nitrogen-vacancy defect in diamond and is underpinned, theoretically, by the formulation of a generalized fluctuation theorem designed to track the effects of quantum coherence. Our results provide significant evidence of the possibility to pinpoint the genuinely quantum mechanical contributions to the thermodynamics of non-equilibrium quantum processes in an open quantum systems scenario.

Opportunities for diamond quantum metrology in biological systems

Sensors that harness quantum mechanical effects can enable high sensitivity and high spatial resolution probing of their environment. The nitrogen-vacancy defect in diamond, a single, optically accessible electronic spin, is a promising quantum sensor that can operate in soft and living systems and provides nanoscale spatial resolution when hosted inside a diamond nanoparticle. Nanodiamond quantum sensors are nontoxic, amenable to surface functionalization, and can be introduced into a variety of living systems. The optical readout of the spin provides detailed information about the local electromagnetic and thermal environment in a noninvasive way. In this Perspective, we introduce the different modalities that nanodiamond quantum sensors offer, highlight recent progress in quantum sensing of biological systems, and discuss remaining challenges and directions for future efforts.

Sub-nanotesla sensitivity at the nanoscale with a single spin.

High-sensitivity detection of the microscopic magnetic field is essential in many fields. Good sensitivity and high spatial resolution are mutually contradictory in measurement, which is quantified by the energy resolution limit. Here we report that a sensitivity of 0.5nT/[Formula: see text] at the nanoscale is achieved experimentally by using nitrogen-vacancy defects in diamond with depths of tens of nanometers. The achieved sensitivity is substantially enhanced by integrating with multiple quantum techniques, including real-time-feedback initialization, dynamical decoupling with shaped pulses and repetitive readout via quantum logic. Our magnetic sensors will shed new light on searching new physics beyond the standard model, investigating microscopic magnetic phenomena in condensed matters, and detection of life activities at the sub-cellular scale.

High efficiency radio frequency antennas for amplifier free quantum sensing applications

Radio frequency (RF) signals are frequently used in emerging quantum applications due to their spin state manipulation capability. Efficient coupling of RF signals into a particular quantum system requires the utilization of carefully designed and fabricated antennas. Nitrogen vacancy (NV) defects in diamond are commonly utilized platforms in quantum sensing experiments with the optically detected magnetic resonance (ODMR) method, where an RF antenna is an essential element. We report on the design and fabrication of high efficiency coplanar RF antennas for quantum sensing applications. Single and double ring coplanar RF antennas were designed with −37 dB experimental return loss at 2.87 GHz, the zero-field splitting frequency of the negatively charged NV defect in diamond. The efficiency of both antennas was demonstrated in magnetic field sensing experiments with NV color centers in diamond. An RF amplifier was not needed, and the 0 dB output of a standard RF signal generator was adequate to run the ODMR experiments due to the high efficiency of the RF antennas.

Impacts of nitrogen concentration and electron irradiation fluence on the formation of nitrogen-vacancy defects in diamond

Impacts of nitrogen concentration and electron irradiation fluence on the formation of nitrogen-vacancy defects in diamond

Screened configuration interaction method for open-shell excited states applied to NV centers

We present a computational approach, based on density functional theory and screened configuration interaction, able to accurately treat highly correlated electron spins localized around semiconductor defects, typically occurring in the context of qubit implementations. The method is computationally not more demanding than a usual density functional theory calculation, which makes it suitable for the calculation of isolated defects, or defect complexes, typically requiring large simulation cells. We illustrate the approach by applying it to the three different charge states of the nitrogen vacancy defect in diamond and obtain very good agreement with experiment.

Quantitative study of the response of a single NV defect in diamond to magnetic noise

The nitrogen-vacancy (NV) defect in diamond is an efficient quantum sensor of randomly fluctuating signals via relaxometry measurements. In particular, the longitudinal spin relaxation of the NV defect accelerates in the presence of magnetic noise with a spectral component at its electron spin resonance frequency. We look into this effect quantitatively by applying a calibrated and tunable magnetic noise on a single NV defect. We show that an increase of the longitudinal spin relaxation rate translates into a reduction of the photoluminescence (PL) signal emitted under continuous optical illumination, which can be explained using a simplified three-level model of the NV defect. This PL quenching mechanism offers a simple, all-optical method to detect magnetic noise sources at the nanoscale.

Characterization of room-temperature in-plane magnetization in thin flakes of CrTe2 with a single-spin magnetometer

We demonstrate room-temperature ferromagnetism with in-plane magnetic anisotropy in thin flakes of the $\mathrm{Cr}{\mathrm{Te}}_{2}$ van der Waals ferromagnet. Using quantitative magnetic imaging with a single-spin magnetometer based on a nitrogen-vacancy defect in diamond, we infer a room-temperature in-plane magnetization in the range of $M\ensuremath{\sim}27$ kA/m for flakes with thicknesses down to 20 nm. In addition, our measurements indicate that the orientation of the magnetization is not determined solely by shape anisotropy in micron-sized $\mathrm{Cr}{\mathrm{Te}}_{2}$ flakes, which suggests the existence of a non-negligible magnetocrystalline anisotropy. These results make $\mathrm{Cr}{\mathrm{Te}}_{2}$ a unique system in the growing family of van der Waals ferromagnets, as it is the only material platform known to date that offers an intrinsic in-plane magnetization and a Curie temperature above 300 K in thin flakes.

High resolution imaging with anomalous saturated excitation

The nonlinear fluorescence emission has been widely applied for high spatial resolution optical imaging. Here, we studied the fluorescence anomalous saturating effect of the nitrogen vacancy defect in diamond. The fluorescence reduction was observed with high power laser excitation. It increased the nonlinearity of the fluorescence emission, and changed the spatial frequency distribution of the fluorescence image. We used a differential excitation protocol to extract the high spatial frequency information. By modulating the excitation laser’s power, the spatial resolution of imaging was improved approximately 1.6 times in comparison with the confocal microscopy. Due to the simplicity of the experimental setup and data processing, we expect this method can be used for improving the spatial resolution of sensing and biological labeling with the defects in solids.

An ab initio effective solid-state photoluminescence by frequency constraint of cluster calculation

Measuring the photoluminescence of defects in crystals is a common experimental technique for analysis and identification. However, current theoretical simulations typically require the simulation of a large number of atoms to eliminate finite-size effects, which discourages computationally expensive excited state methods. We show how to extract the room-temperature photoluminescence spectra of defect centers in bulk from an ab initio simulation of a defect in small clusters. The finite-size effect of small clusters manifests as strong coupling to low frequency vibrational modes. We find that removing vibrations below a cutoff frequency determined by constrained optimization returns the main features of the solid-state photoluminescence spectrum. This strategy is illustrated for the negatively charged nitrogen vacancy defect in diamond (NV−) presenting a connection between defects in solid state and clusters; the first vibrationally resolved ab initio photoluminescence spectrum of an NV− defect in a nanodiamond; and an alternative technique for simulating photoluminescence for solid-state defects utilizing more accurate excited state methods.

Spin-enhanced nanodiamond biosensing for ultrasensitive diagnostics.

The quantum spin properties of nitrogen-vacancy defects in diamond enable diverse applications in quantum computing and communications1. However, fluorescent nanodiamonds also have attractive properties for in vitro biosensing, including brightness2, low cost3 and selective manipulation of their emission4. Nanoparticle-based biosensors are essential for the early detection of disease, but they often lack the required sensitivity. Here we investigate fluorescent nanodiamonds as an ultrasensitive label for in vitro diagnostics, using a microwave field to modulate emission intensity5 and frequency-domain analysis6 to separate the signal from background autofluorescence7, which typically limits sensitivity. Focusing on the widely used, low-cost lateral flow format as an exemplar, we achieve a detection limit of 8.2×10-19 molar for a biotin-avidin model, 105times more sensitive than that obtained using gold nanoparticles. Single-copy detection of HIV-1 RNA can be achieved with the addition of a 10-minute isothermal amplification step, and is further demonstrated using a clinical plasma sample with an extraction step. This ultrasensitive quantumdiagnostics platform is applicable to numerous diagnostic test formats and diseases, and has the potential to transform early diagnosis of disease for the benefit of patients and populations.

Multiphoton resonances in nitrogen-vacancy defects in diamond

Dense ensembles of nitrogen vacancy (NV) centers in diamond are of interest for various applications including magnetometry, masers, hyperpolarization and quantum memory. All of the applications above may benefit from a non-linear response of the ensemble, and hence multiphoton processes are of importance. We study an enhancement of the NV ensemble multiphoton response due to coupling to a superconducting cavity or to an ensemble of Nitrogen 14 substitutional defects (P1). In the latter case, the increased NV sensitivity allowed us to probe the P1 hyperfine splitting. As an example of an application, an increased responsivity to magnetic field is demonstrated.

Detection of paramagnetic defects in diamond using off-resonance excitation of NV centers

In this work we use fluorescence from nitrogen-vacancy defects in diamond to detect and explore other paramagnetic defects in the diamond, such as P1 defects, which are commonly undetectable through optical detection of magnetic resonance in standard conditions. Our method does not require overlap between the defects' resonances and therefore is applicable in a wide region of magnetic fields and frequencies, as verified by excellent fit to theoretical predictions. We propose a depolarization scheme of P1 defects to account for the observed data. To verify our results, we perform cavity-based detection of magnetic resonance and find a good agreement between the measured optically induced polarization and the value obtained theoretically from rate equations. The findings in this work may open the way to detection of paramagnetic defects outside of the diamond through the photoluminesence of nitrogen-vacancy defects, which might be useful for imaging in biology.

Laser writing of individual nitrogen-vacancy defects in diamond with near-unity yield

Atomic defects in wide band gap materials show great promise for development of a new generation of quantum information technologies, but have been hampered by the inability to produce and engineer the defects in a controlled way. The nitrogen-vacancy (NV) color center in diamond is one of the foremost candidates, with single defects allowing optical addressing of electron spin and nuclear spin degrees of freedom with potential for applications in advanced sensing and computing. Here we demonstrate a method for the deterministic writing of individual NV centers at selected locations with high positioning accuracy using laser processing with online fluorescence feedback. This method provides a new tool for the fabrication of engineered materials and devices for quantum technologies and offers insight into the diffusion dynamics of point defects in solids.

Magnetic resonance spectroscopy and imaging based on quantum controls of nitrogen-vacancy defects in diamond

Magnetic resonance spectroscopy and imaging based on quantum controls of nitrogen-vacancy defects in diamond

Using nitrogen-vacancy defects in diamond as in-situ sensors of band bending

Using nitrogen-vacancy defects in diamond as in-situ sensors of band bending

Identification and tunable optical coherent control of transition-metal spins in silicon carbide

Color centers in wide-bandgap semiconductors are attractive systems for quantum technologies since they can combine long-coherent electronic spin and bright optical properties. Several suitable centers have been identified, most famously the nitrogen-vacancy defect in diamond. However, integration in communication technology is hindered by the fact that their optical transitions lie outside telecom wavelength bands. Several transition-metal impurities in silicon carbide do emit at and near telecom wavelengths, but knowledge about their spin and optical properties is incomplete. We present all-optical identification and coherent control of molybdenum-impurity spins in silicon carbide with transitions at near-infrared wavelengths. Our results identify spin S = 1/2 for both the electronic ground and excited state, with highly anisotropic spin properties that we apply for implementing optical control of ground-state spin coherence. Our results show optical lifetimes of ~60 ns and inhomogeneous spin dephasing times of ~0.3 μs, establishing relevance for quantum spin-photon interfacing.

Bethe-Salpeter Equation calculations of nitrogen-vacancy defects in diamond

Doped diamonds are of significant fundamental, technological, and commercial interest. For example, boron doping leads to a blue coloration at low concentration and superconductivity at high concentration. Similarly nitrogen doping can cause a variety of colors in diamond. Nitrogen-vacancy defects are also promising as quantum-computing qubits. Theoretical Bethe-Salpeter Equation (BSE) simulations of boron-doped diamonds have been found to give optical absorption spectra in good agreement with their observed blue coloration. In contrast, nitrogen defects are more complex, due in part to a plethora of possible N-defect conformations. Here we present a theoretical study of several neutral, isolated, N-defect conformations that combines ab initio DFT calculations for relaxed 64-atom unit cells together with first principles GW/BSE calculations of their optical spectra. Spectral results are compared with available experimental data, and the effects of absorption are simulated for realistic rendered diamonds.

Robust, tunable, and high purity triggered single photon source at room temperature using a nitrogen-vacancy defect in diamond in an open microcavity.

We report progress in the development of tunable room temperature triggered single photon sources based on single nitrogen-vacancy (NV) centres in nanodiamond coupled to open access optical micro-cavities. The feeding of fluorescence from an NV centre into the cavity mode increases the spectral density of the emission and results in an output stream of triggered single photons with spectral line width of order 1 nm, tunable in the range 640 - 700 nm. We record single photon purities exceeding 96% and estimated device efficiencies up to 3%. We compare performance using plano-concave microcavities with radii of curvature from 25 μm to 4 μm and show that up to 17% of the total emission is fed into the TEM00 mode. Pulsed Hanbury-Brown Twiss (HBT) interferometry shows that an improvement in single photon purity is facilitated due to the increased spectral density.

Real-space imaging of non-collinear antiferromagnetic order with a single-spin magnetometer.

Although ferromagnets have many applications, their large magnetization and the resulting energy cost for switching magnetic moments bring into question their suitability for reliable low-power spintronic devices. Non-collinear antiferromagnetic systems do not suffer from this problem, and often have extra functionalities: non-collinear spin order may break space-inversion symmetry and thus allow electric-field control of magnetism, or may produce emergent spin-orbit effects that enable efficient spin-charge interconversion. To harness these traits for next-generation spintronics, the nanoscale control and imaging capabilities that are now routine for ferromagnets must be developed for antiferromagnetic systems. Here, using a non-invasive, scanning single-spin magnetometer based on a nitrogen-vacancy defect in diamond, we demonstrate real-space visualization of non-collinear antiferromagnetic order in a magnetic thin film at room temperature. We image the spin cycloid of a multiferroic bismuth ferrite (BiFeO3) thin film and extract a period of about 70 nanometres, consistent with values determined by macroscopic diffraction. In addition, we take advantage of the magnetoelectric coupling present in BiFeO3 to manipulate the cycloid propagation direction by an electric field. Besides highlighting the potential of nitrogen-vacancy magnetometry for imaging complex antiferromagnetic orders at the nanoscale, these results demonstrate how BiFeO3 can be used in the design of reconfigurable nanoscale spin textures.