Ensemble Of Nitrogen-vacancy Centers Research Articles

Nanoscale covariance magnetometry with diamond quantum sensors

Nitrogen vacancy (NV) centers in diamond are atom-scale defects that can be used to sense magnetic fields with high sensitivity and spatial resolution. Typically, the magnetic field is measured by averaging sequential measurements of single NV centers, or by spatial averaging over ensembles of many NV centers, which provides mean values that contain no nonlocal information about the relationship between two points separated in space or time. Here, we propose and implement a sensing modality whereby two or more NV centers are measured simultaneously, and we extract temporal and spatial correlations in their signals that would otherwise be inaccessible. We demonstrate measurements of correlated applied noise using spin-to-charge readout of two NV centers and implement a spectral reconstruction protocol for disentangling local and nonlocal noise sources.

Transfer of arbitrary quantum states between separated superconducting cavities via an ensemble of nitrogen-vacancy centers

Transfer of quantum states between distant nodes is one of the most important preconditions for realizing large-scale quantum information processing. We here propose two ways to transfer an arbitrary quantum state between two separated superconducting cavities coupled to an ensemble of nitrogen-vacancy centers (NV ensemble). By using the double-swap scheme and theory of the dispersive regime, quantum states can be deterministically transferred between two superconducting cavities. With current hybrid circuit QED technology, the numerical simulations are performed to demonstrate that the single-photon state and cat state can be high-fidelity transferred between two superconducting cavities.

Broadband microwave antenna for uniform manipulation of millimeter-scale volumes of diamond quantum sensors

Quantum sensors based on nitrogen-vacancy (NV) centers in diamond are expected to demonstrate a wide variety of applications. For high-sensitivity quantum sensors with NV center ensembles, uniform manipulation of the electron spins of the NV centers in large volumes is required. In addition, a broad microwave frequency bandwidth for manipulating the NV centers' electron spin is necessary for vector magnetometry and measurement under a finite static magnetic field. Here, we demonstrate a broadband microwave antenna for uniform manipulation of millimeter-scale volumes of diamond quantum sensors. The simulation shows that the current is distributed at both edges of the loop coil of a single copper plate due to the skin effect. The loop coil acts like a Helmholtz coil, which realizes uniformity in the z-direction of the microwave magnetic field (B1). The plate structure has a higher mechanical stability, durability, and a larger heat capacity than the Helmholtz coil, due to its large volume. The antenna achieves a higher performance than previously reported antennae, with a maximal B1 of 4.5 G, a broad bandwidth of 287 ± 6 MHz, and a peak-to-peak variation of 9.2% over a 3.1 mm3 cylinder volume. These performances show that the presented antenna is suitable for manipulating solid-state spin ensembles for high-sensitivity quantum sensors.

Wide-field microwave imaging using nitrogen-vacancy center ensembles in diamond

Microwave chips dependent devices constitute the cornerstone of many classical and emerging quantum technologies. To meet the demand for high-resolution, lossless, and fast wide-field imaging of microwave devices, we propose a wide-field microwave imaging method based on diamond nitrogen-vacancy center ensembles by combining continuous wave optically detected magnetic resonance technology with optical wide-field imaging technology. First, the optimal selection of laser parameters is achieved by measuring different laser powers. Then the accuracy of the wide-field microwave imaging technique is demonstrated by measuring the near-field imaging of the antenna surface at different microwave input powers and different microwave input frequencies. The spatial resolution of the imaging system is 5 μm over a field of view of 2400 μm × 1350 μm, and the optimal microwave precision measurement sensitivity is 5.6 μT / Hz1/2. The above results are expected to provide a practical reference for applications such as fault diagnosis of highly integrated microwave circuits, antenna radiation profiling, and electro magnetic compatibility testing of integrated microwave circuits.

Stabilization of spin states of an open system: bichromatic driving of resonance transitions in NV ensembles in diamond.

We apply a laser and two nearly degenerate microwave fields upon an ensemble of nitrogen-vacancy centers in diamond and observe magnetic resonance structures with two-component, composite shapes of nested Lorentzians with different widths. One component of them undergoes regular power-broadening, whereas the linewidth of the other one becomes power-independent and undergoes field-induced stabilization. We show that the observed width stabilization is a general phenomenon that results from competition between coherent driving and non-conservation of populations that occur in open systems. The phenomenon is interpreted in terms of specific combinations of state populations that play the role of bright and dark states.

New constraints on exotic spin-dependent interactions with an ensemble-NV-diamond magnetometer.

Laboratory search of exotic interactions is crucial for exploring physics beyond the standard model. We report new experimental constraints on two exotic spin-dependent interactions at the micrometer scale based on ensembles of nitrogen-vacancy (NV) centers in diamond. A thin layer of NV electronic spin ensembles is synthesized as the solid-state spin quantum sensor, and a lead sphere is taken as the interacting nucleon source. Our result establishes new bounds for two types of exotic spin interactions at the micrometer scale. For an exotic parity-odd spin- and velocity-dependent interaction, improved bounds are set within the force range from 5 to 500μm. The upper limit of the corresponding coupling constant [Formula: see text] at 330μm is more than 1000-fold more stringent than the previous constraint. For the P, T-violating scalar-pseudoscalar nucleon-electron interaction, improved constraints are established within the force range from 6 to 45μm. The limit of the corresponding coupling constant [Formula: see text] is improved by more than one order of magnitude at 30μm. This work demonstrates that a solid-state NV ensemble can be a powerful platform for probing exotic spin-dependent interactions.

Quantum Dynamics of Two Nitrogen-Vacancy Center Ensembles Coupled to a Driven Superconducting Quantum Circuit

We theoretically model and simulate the dynamics of a hybrid quantum system consisting of two non-local ensembles of nitrogen-vacancy center and a superconducting transmon qubit mediated by two transmission line resonators. We apply a time-dependent external field to enhance this system’s speed and fidelity to function as a controlled-phase gate. Our simulation result shows that a high-fidelity entangled state of two non-local NV spins is 92%. It is achievable under realistic parameter regimes within a timescale of 1.1 nanoseconds. Our result paves the way to improving potential quantum computing and sensing applications.

Wide-field tomography imaging of a double circuit using NV center ensembles in a diamond.

The wide-field (2.42 mm × 1.36 mm, resolution: 5.04 µm) tomography imaging of double circuits is performed using nitrogen-vacancy (NV) center ensembles in a diamond. The magnetic-field distribution on the surface of the circuit produced by the lower layer is obtained. Vector magnetic superposition is used to separate the magnetic-field distribution produced by the lower layer from the magnetic-field distribution produced by two layers. An inversion model is used to perform the tomography imaging of the magnetic-field distribution on the lower layer surface. Compared with the measurements of the upper layer, the difference in the maximum magnetic-field intensity of inversion is approximately 0.4%, and the difference in the magnetic-field distribution of inversion is approximately 8%, where the depth of the lower layer is 0.32 mm. Simulations are conducted to prove the reliability of the imaging. These results provide a simple and highly accurate reference for the detection and fault diagnosis of multilayer and integrated circuits.

Divergent Effects of Laser Irradiation on Ensembles of Nitrogen-Vacancy Centers in Bulk and Nanodiamonds: Implications for Biosensing.

Ensembles of negatively charged nitrogen-vacancy centers (NV−) in diamond have been proposed for sensing of magnetic fields and paramagnetic agents, and as a source of spin-order for the hyperpolarization of nuclei in magnetic resonance applications. To this end, strongly fluorescent nanodiamonds (NDs) represent promising materials, with large surface areas and dense ensembles of NV−. However, surface effects tend to favor the less useful neutral form, the NV0 centers, and strategies to increase the density of shallow NV− centers have been proposed, including irradiation with strong laser power (Gorrini in ACS Appl Mater Interfaces. 13:43221–43232, 2021). Here, we study the fluorescence properties and optically detected magnetic resonance (ODMR) of NV− centers as a function of laser power in strongly fluorescent bulk diamond and in nanodiamonds obtained by nanomilling of the native material. In bulk diamond, we find that increasing laser power increases ODMR contrast, consistent with a power-dependent increase in spin-polarization. Conversely, in nanodiamonds we observe a non-monotonic behavior, with a decrease in ODMR contrast at higher laser power. We hypothesize that this phenomenon may be ascribed to more efficient NV−→NV0 photoconversion in nanodiamonds compared to bulk diamond, resulting in depletion of the NV− pool. A similar behavior is shown for NDs internalized in macrophage cells under the typical experimental conditions of imaging bioassays. Our results suggest strong laser irradiation is not an effective strategy in NDs, where the interplay between surface effects and local microenvironment determine the optimal experimental conditions.Supplementary InformationThe online version contains supplementary material available at 10.1186/s11671-022-03723-2.

A quantum radio frequency signal analyzer based on nitrogen vacancy centers in diamond

The rapid development of radio-frequency (RF) technologies requires tools which can efficiently monitor the electromagnetic landscape. Broadband real-time RF spectral analyzers need to operate at room temperature, with low power consumption and have a compact design for on-board device integration. Here we describe a Quantum Diamond Signal Analyzer (Q-DiSA) which detects RF signals over a tunable frequency range of 25 GHz with frequency resolution down to 1 MHz, a millisecond temporal resolution and a large dynamic range (40 dB). This approach exploits the room temperature spin properties of an ensemble of nitrogen-vacancy (NV) centers in diamond. Performance is enabled via our analyzer architecture which combines a specific diamond crystallographic cut with a simplified magnetic arrangement. This allows us to maintain the alignment of the magnetic field along the nitrogen-vacancy center axis whilst frequency tuning. These results demonstrate the potential of the Q-DiSA method for real-time broadband spectral analysis.

Design of an ultra-sensitive and miniaturized diamond NV magnetometer based on a nanocavity structure

The ensemble of nitrogen-vacancy (NV) centers in diamond allows for the potential realization of the sensitive magnetometers by leveraging their excellent spin properties. However, the NV-based magnetometers are limited by their experimental magnetic field sensitivity owing to its inefficient photon collection. Moreover, they are a disadvantage to the reduced spatial resolution and excessive excitation power. To overcome these issues, we propose a ultra-sensitive diamond magnetometer based on nanocavities. The device structure can attain a high collective efficiency and enhance the photon emission intensity of the NV ensemble. This device can allow the efficient photon collection even when considering the positional distribution of the NV centers. Our theoretical analysis indicates that the minimum expected sensitivity is 60 fT/ The proposed design can achieve a volume-normalized sensitivity of 0.92 aT/ along with the required power of 7 μW, both of which are superior to those of bulk diamond. The proposed approach offers a promising route towards highly sensitive and energy-efficient magnetometers.

High-sensitivity temperature sensing on an ensemble of nitrogen-vacancy centers in diamond

We demonstrate a method for thermal detection that is the sensitivity 6.2 mK Hz−1 2, which uses the frequency lock closed-loop scheme to track Zeeman-split resonance of nitrogen-vacancy (NV) centers in diamond. The NV diamond surface acts as a temperature measurement sensor to transfer the temperature variation as D(T) parameter change to lead to the movement of the energy levels to detect the temperature. By frequency modulation technology and closed-loop feedback locking technology, automatic temperature detection and step signal reading are realized, with a resolution of 7.6 mK. It is found that the closed-loop output is basically unchanged, while the open-loop output has an error signal proportional to the laser fluctuation. The closed-loop feedback technique can improve the stability and resolution of the system and provides a method for measuring the actual temperature detection. Such a demonstration marks a vital advance in transitioning the NV thermometer from a laboratory system to a functional device for detecting temperature fields in a practical environment.

Investigating the size effect on the electrical conductivity at nanoscale with solid spins

With the miniaturization of electrical components at nanoscale, the impact of dimension and shape on the electrical properties of the devices plays an important role in the applications. In this work, we used an ensemble of nitrogen-vacancy (NV) centers in diamond to noninvasively investigate the size effect on electric conductivity at nanoscale. The magnetic noise originated from the random movement of electrons in conductors, which is related to the conductivity, was detected by recording the spin relaxation of NV centers. The results indicate that the conductivity increases with the size of devices at the scale of electron mean free path. By further imaging the magnetic noise of the metallic structure with discontinuous thickness, we demonstrated that the spatial distribution of conductance at nanoscale can be revealed with high density NV center arrays. The results can help to understand the electron transport in nanomaterials. This technique can be used to optimize the design of nanoscale electrical devices.

Optically induced static magnetic field in the ensemble of nitrogen-vacancy centers in diamond.

Generation of a local magnetic field at the nanoscale is desirable for many applications such as spin-qubit-based quantum memories. However, this is a challenge due to the slow decay of static magnetic fields. Here, we demonstrate a photonic spin density (PSD)-induced effective static magnetic field for an ensemble of nitrogen-vacancy (NV) centers in bulk diamond. This locally induced magnetic field is a result of coherent interaction between the optical excitation and the NV centers. We demonstrate an optically induced spin rotation on the Bloch sphere exceeding 10 degrees which has potential applications in all-optical coherent control of spin qubits.

Towards the design and operation of a uniformly illuminated NV detector for magnetic field mapping applications

Detectors based on an ensemble of nitrogen-vacancy (NV) centres in diamond are the latest addition to the list of magnetometers capable of detecting weak magnetic fields. Here, we report the design, construction, and testing of an NV magnetometer with a wide spatial area excitation and collection capability. The system was developed for the purpose of magnetic field measurement in an Halbach magnet configuration. The designed system performance was comparable to a conventional NV confocal system in the low power excitation region. From the dip profiles observed in the optically detected magnetic resonance (ODMR) spectrum, each NV centre experienced a static magnetic field in the 2.14–6.07 mT range of the Halbach magnet. The sensitivity of the field mapping system using the continuous wave (CW)-ODMR approach was estimated and found to be approximately 0.2 μT/Hz at 170 MHz. Extensive details of the setup and the experimental procedures are presented, and the system can be easily reproduced by those who are not familiar with NV centre instrumentation. The results obtained pave way for the development of scalable NV sensors using wide area illumination and collection methods, especially for the mapping B0 and B1 field in magnetic resonance imaging (MRI) to facilitate non-FFT image reconstruction.

Magnetic-field-dependent stimulated emission from nitrogen-vacancy centers in diamond.

Negatively charged nitrogen-vacancy (NV) centers in diamond are promising magnetic field quantum sensors. Laser threshold magnetometry theory predicts improved NV center ensemble sensitivity via increased signal strength and magnetic field contrast. Here, we experimentally demonstrate laser threshold magnetometry. We use a macroscopic high-finesse laser cavity containing a highly NV-doped and low absorbing diamond gain medium that is pumped at 532 nm and resonantly seeded at 710 nm. This enables a 64% signal power amplification by stimulated emission. We test the magnetic field dependency of the amplification and thus demonstrate magnetic field–dependent stimulated emission from an NV center ensemble. This emission shows an ultrahigh contrast of 33% and a maximum output power in the milliwatt regime. The coherent readout of NV centers pave the way for novel cavity and laser applications of quantum defects and diamond NV magnetic field sensors with substantially improved sensitivity for the health, research, and mining sectors.

One-step construction of a multi-qubit controlled phase gate with ensembles of nitrogen-vacancy centers in hybrid circuit QED

One-step construction of a multi-qubit controlled phase gate with ensembles of nitrogen-vacancy centers in hybrid circuit QED

A microfabricated fiber-integrated diamond magnetometer with ensemble nitrogen-vacancy centers

Miniaturization is a trend of development toward practical applications for diamond nitrogen-vacancy centers-based sensors. We demonstrate a compact diamond magnetic field sensor device using a standard microfabrication process. A single-crystal-diamond plate is embedded in a cavity formed with stacking of three silicon chips. Thermal compression bonding is implemented at silicon–silicon and diamond–silicon interfaces ensuring mechanical robustness. The specific construction volume for the essential sensor component is about 10 × 10 × 1.5 mm3. By integrating a gradient index lens pigtailed fiber to the sensor device, 532-nm laser light and emitted fluorescence share a common path for excitation and detection. An omega-shaped transmission line for applied microwave power is fabricated directly on the surface of diamond. The integrated sensor device exhibits an optimized sensitivity of 2.03 nT·Hz−1/2 and over twofold enhancement of fluorescence collection efficiency compared to bare diamond. Such a sensor is utilized to measure a magnetic field change caused by switching a household electrical appliance.

Optical and Spin Properties of NV Center Ensembles in Diamond Nano-Pillars.

Nitrogen-vacancy (NV) color centers in diamond are excellent quantum sensors possessing high sensitivity and nano-scale spatial resolution. Their integration in photonic structures is often desired, since it leads to an increased photon emission and also allows the realization of solid-state quantum technology architectures. Here, we report the fabrication of diamond nano-pillars with diameters up to 1000 nm by electron beam lithography and inductively coupled plasma reactive ion etching in nitrogen-rich diamonds (type Ib) with [100] and [111] crystal orientations. The NV centers were created by keV-He ion bombardment and subsequent annealing, and we estimate an average number of NVs per pillar to be 4300 ± 300 and 520 ± 120 for the [100] and [111] samples, respectively. Lifetime measurements of the NVs’ excited state showed two time constants with average values of τ1 ≈ 2 ns and τ2 ≈ 8 ns, which are shorter as compared to a single color center in a bulk crystal (τ ≈ 10 ns). This is probably due to a coupling between the NVs as well as due to interaction with bombardment-induced defects and substitutional nitrogen (P1 centers). Optically detected magnetic resonance measurements revealed a contrast of about 5% and average coherence and relaxation times of T2 [100] = 420 ± 40 ns, T2 [111] = 560 ± 50 ns, and T1 [100] = 162 ± 11 μs, T1 [111] = 174 ± 24 μs. These pillars could find an application for scanning probe magnetic field imaging.

High growth rate synthesis of diamond film containing perfectly aligned nitrogen-vacancy centers by high-power density plasma CVD

Diamond film sensors with large volumes that are synthesized by microwave plasma chemical vapor deposition (MPCVD) and contain perfectly aligned nitrogen-vacancy (NV) ensembles are promising material for achieving highly sensitive quantum magnetometers. The step-flow growth mode of MPCVD on diamond (111) surface is required to realize aligned NV center ensembles. However, it is difficult to control the growth mode on diamond (111) surface due to the presence of twins and the conventional growth rate of aligned NV center ensembles is lower than 0.5 μm/h. In this study, we achieved a high growth rate (6.6 μm/h) of diamond (111) film containing perfectly aligned NV ensembles with high contrast (30%) by applying high power density plasma (103 W/cm3) and precisely controlling the gas flow rate ratios of CH4/H2 and N2/CH4. The growth mode was controlled to realize step flow growth by inducing the hydrogen etching of the nucleation with decreasing the CH4/H2. It was considered that increasing the microwave power density produces a large amount of atomic hydrogen and carbon precursor, leading to a high growth rate of perfectly aligned NV center diamond film. By controlling the N2/CH4 ratio, the nitrogen density in the diamond film could be precisely controlled to obtain a high contrast. Moreover, we measured the quality of the obtained diamond sensor films using the ODMR spectra and Ramsey sequence. We confirmed a high Rabi contrast (approximately 30%) and no significant decrease in T2∗ due to the deterioration of the crystallinity of the diamond film was observed. This result is promising for building material technology for highly sensitive quantum sensors with large sensor volumes.