A Bright Single-Photon Source from Nitrogen-Vacancy Centers in Diamond Nanowires

Single-photon flux is one of the crucial properties of nitrogen vacancy （NV） centers in diamond for its application in quantum information techniques. Here we fabricate diamond conical nanowires to enhance the single-photon count rate. Through the interaction between tightly confined optical mode in nanowires and NV centers, the single-photon lifetime is much shortened and the collection efficiency is enhanced. As a result, the detected single-photon rate can be at 564 kcps, and the total detection coefficient can be 0.8%, which is much higher than that in bulk diamond. Such a nanowire single-photon device with high photon flux can be applied to improve the fidelity of quantum computation and the precision of quantum sensors.

Current sensor based on diamond nitrogen-vacancy color center

High precision current measurement is very important for the calibration of various high-precision equipment and the measurement of other precision detection fields.A new current sensor based on diamond nitrogen-vacancy(NV)color center magnetic measurement method is proposed to realize the accurate measurement of current.This new current method can greatly improve the accuracy of current measurement.Experiments show that the linearity of the current sensor based on diamond NV color center can reach up to 33 ppm,which is superior to other current sensors and solves the problem of low linearity.When the range of input current is 5-40 A,the absolute error of the calculated current is less than 51μA,and the relative error is 2.42×10^(-6) at 40 A.Combined with the research content and results of the experiment,the application of the current sensor in the field of current precision measurement is prospected.

Non-destructive Testing Method for Crack Based on Diamond Nitrogen-vacancy Color Center

Magnetic field measurement plays an extremely important role in material science,electronic en-gineering,power system and even industrial fields.In particular,magnetic field measurement provides a safe and reliable tool for industrial non-destructive testing.The sensitivity of magnetic field measurement deter-mines the highest level of detection.The diamond nitrogen-vacancy(NV)color center is a new type of quan-tum sensor developed in recent years.The external magnetic field will cause Zeeman splitting of the ground state energy level of the diamond NV color center.Optical detection magnetic resonance(ODMR),using a mi-crowave source and a lock-in amplifier to detect the resonant frequency of the NV color center,and finally the change of the resonant frequency can accurately calculate the size of the external magnetic field and the sensi-tivity of the external magnetic field change.In the experiment,a diamond containing a high concentration of NV color centers is coupled with an optical fiber to realize the preparation of a magnetic field scanning probe.Then,the surface cracks of the magnetized iron plate weld are scanned,and the scanning results are drawn into a two-dimensional magnetic force distribution map,according to the magnetic field gradient change of the magnetic force distribution map,the position and size of the crack can be judged very accurately,which pro-vides a very effective diagnostic tool for industrial safety.

Magnetic field analysis in a diamond anvil cell for Meissner effect measurement by using the diamond NV^- center

Diamond negatively charged nitrogen-vacancy(NV-) centers provide an opportunity for the measurement of the Meissner effect on extremely small samples in a diamond anvil cell(DAC) due to their high sensitivity in detecting the tiny change of magnetic field. We report on the variation of magnetic field distribution in a DAC as a sample transforms from normal to superconducting state by using finite element analysis. The results show that the magnetic flux density has the largest change on the sidewall of the sample, where NV-centers can detect the strongest signal variation of the magnetic field. In addition, we study the effect of magnetic coil placement on the magnetic field variation. It is found that the optimal position for the coil to generate the greatest change in magnetic field strength is at the place as close to the sample as possible.

Design and simulation of an accelerometer based on NV center spin–strain coupling

The nitrogen-vacancy (NV) center quantum systems have emerged as versatile tools in the field of precision measurement because of their high sensitivity in spin state detection and miniaturization potential as solid-state platforms.In this paper,an acceleration sensing scheme based on NV spin–strain coupling is proposed,which can effectively eliminate the influence of the stray noise field introduced by traditional mechanical schemes.Through the finite element simulation,it is found that the measurement bandwidth of this ensemble NV spin system ranges from 3 kHz to hundreds of kHz with structure√optimization.The required power is at the sub-μW level,corresponding to a noise-limited sensitivity of 6.7×10^(-5) /√Hz.Compared with other types of accelerometers,this micro-sized diamond sensor proposed here has low power consumption,exquisite sensitivity,and integration potential.This research opens a fresh perspective to realize an accelerometer with appealing comprehensive performance applied in biomechanics and inertial measurement fields.

Dependence of nitrogen vacancy color centers on nitrogen concentration in synthetic diamond

Crystallization of diamond with different nitrogen concentrations was carried out with a FeNiCo-C system at pressure of 6.5 GPa.As the nitrogen concentration in diamond increased,the color of the synthesized diamond crystals changed from colorless to yellow and finally to atrovirens(a dark green).All the Raman peaks for the obtained crystals were located at about 1330 cm^(-1)and contained only the sp^(3)hybrid diamond phase.Based on Fourier transform infrared results,the nitrogen concentration of the colorless diamond was<1 ppm and absorption peaks corresponding to nitrogen impurities were not detected.However,the C-center nitrogen concentration of the atrovirens diamond reached 1030 ppm and the value of A-center nitrogen was approximately 180 ppm with a characteristic absorption peak at 1282 cm^(-1).Furthermore,neither the NV^(0)nor the NV^(-)optical color center existed in diamond crystal with nitrogen impurities of less than 1 ppm by photoluminescence measurement.However,Ni-related centers located at 695 nm and 793.6 nm were observed in colorless diamond.The NE8 color center at 793.6 nm has more potential for application than the common NV centers.NV^(0)and NV^(-)optical color centers coexist in diamond without any additives in the synthesis system.Importantly,only the NV^(-)color center was noticed in diamond with a higher nitrogen concentration,which maximized optimization of the NV^(-)/NV^(0)ratio in the diamond structure.This study has provided a new way to prepare diamond containing only NV^(-)optical color centers.

Single-channel vector magnetic information detection method based on diamond NV color center

A method of detecting the single channel triaxial magnetic field information based on diamond nitrogen-vacancy(NV)color center is introduced.Firstly,the incident angle of the bias magnetic field which can achieve the equal frequency difference optically-detected magnetic resonance(ODMR)spectrum of diamond NV color center is calculated theoretically,and the triaxial magnetic information solution model is also constructed.Secondly,the microwave time-controlled circuit module is designed to generate equal timing and equal frequency difference microwave pulse signals in one channel.Combining with the optical detection magnetic resonance technology,the purpose of sequentially locking and detecting the four formant signals on one side of the diamond NV color center(m_(s)=-1 state signal)is achieved,and the vector magnetic field information detection is accomplished by combining the triaxial magnetic information solution model.The system can obtain magnetic field detection in a range of 0 mT-0.82 mT.The system's magnetic noise sensitivity is 14.2 nT/Hz^(1/2),and the deviation angle errors of magnetic field detectionθ_(x) andθ_(y) are 1.3° and 8.2° respectively.

An Emerging Testing Method for Metallics Based on NV Center in the Diamond

Metal substance detection plays an extremely important role in daily life,industrial manufacturing and even industrial security.The traditional methods include optical detection,X-ray detection,microwave detection and ultrasonic detection.These methods,playing a vital role in the field of non-destructive testing,can not only judge the presence or absence of metal,but also accurately detect the type and size of metal defects.For microwave detection,the detection efficiency of metal materials is limited by the response sensitivity of the detector to microwaves.In recent years,scientists have discovered a quantum sensing system based on the diamond nitrogen-vacancy(NV)color center.The system obtains optical detection magnetic resonance(ODMR)fluorescence spectra under the combined action of a 532nm laser and a certain frequency band of microwaves,and the signal contrast changes significantly with the microwave power.Based on the NV color center quantum sensing system,this paper studies its application in the field of metal detection,and takes steel detection as an example to detect the size of steel bars according to the changes in the spectral line,providing a new method for non-destructive testing such as metal substance detection.

Transient features of graphitization and nitrogen-vacancy color centers in a diamond fabricated by localization femtosecond laser direct writing

Femtosecond laser direct writing provides an efficient approach to fabricating single nitrogen vacancy(NV) color centers with a relatively high yield. Different from previously reported NV color centers with a random distribution in a bulk diamond or nanocrystals, this gives an opportunity to study the photophysical properties of single NV color centers with precise numbers and positions. However, ultrafast studies on single NV color centers prepared by localization femtosecond laser direct writing are still rare, especially for the graphitization inside a diamond and its relationship with single NV color centers. Here, we report the broadband transient absorption(TA) spectroscopic features of the graphitization and NV color centers in a diamond fabricated by localization femtosecond laser direct writing at room temperature under 400 nm excitation. In comparison with the graphene oxide film, the bleaching features of the graphitization point array in a diamond are similar to reduced graphene oxide,accompanied by excited state absorption signals from local carbon atom vacancy defects in graphene-like structures induced by laser writing. On the other hand, transient features of laser processing array containing single NV color centers with a yield of~50% are different from those of the graphitization point array. Our findings suggest that for ultrashort pulse processing of diamonds, broadband TA spectral signals are sensitive to the surrounding atomic environment of processing sites, which could be applied to laser writing point defects in other materials used as solid-state single photon sources.

Laser-polarization-dependent spontaneous emission of the zero phonon line from single nitrogen vacancy center in diamond

We investigate spontaneous emission properties and control of the zero phonon line （ZPL） from a diamond nitrogen- vacancy （NV） center coherently driven by a single ellipfically polarized control field. We use the Schrrdinger equation to calculate the probability amplitudes of the wave function of the coupled system and derive analytical expressions of the spontaneous emission spectra. The numerical results show that a few interesting phenomena such as enhancement, narrowing, suppression, and quenching of the ZPL spontaneous emission can be realized by modulating the polarization- dependent phase, the Zeeman shift, and the intensity of the control field in our system. In the dressed-state picture of the control field, we find that multiple spontaneously generated coherence arises due to three close-lying states decaying to the same state. These results are useful in real experiments.

近红外光调制下金刚石NV色心自旋动力学与电荷态转化研究

对金刚石氮-空位(nitrogen-vacancy,NV)色心电子自旋态进行光学操控的过程中,近红外光是一种重要手段,对色心自旋态和电荷态布居能产生显著影响,定量研究近红外光对NV色心自旋动力学的作用具有重要意义。文章用实验测量室温下532 nm激光连续激发单个NV色心产生的荧光时间曲线,并建立七能级模型进行数值模拟,得到各自旋能级间跃迁速率;在此基础上用1040 nm激光对色心荧光时间曲线进行调制,实验数据与数值模拟结果相吻合。研究结果表明,近红外光对金刚石NV色心自旋态的影响主要体现在对电荷态转化速率的提高上,使用功率为40 mW的1040 nm激光和532 nm激光一起照射,可以将电离速率和复合速率分别提升约15倍和30倍。

DLC膜对金刚石纳米柱NV色心发光收集强度的影响

金刚石氮空位(NV)色心发光收集强度的提高是实现单光子源技术的关键。本工作将锥状的类金刚石(DLC)梯度减反膜引入纳米柱色心单光子源中,旨在从色心的自发辐射速率与光子收集效率两方面提高NV色心的发光收集强度。采用时域有限差分(FDTD)法对带有DLC膜的金刚石纳米柱复合结构进行了光学仿真,探究了不同结构参数的DLC薄膜对金刚石纳米柱NV色心光子收集强度、出射效率及自发辐射速率的影响,并且通过优化得到了最大收集强度下的结构参数。仿真结果表明,引入DLC膜能够使金刚石纳米柱中NV色心获得更高的光子出射效率(≥1%),并且能够改变纳米柱内部电场分布,使色心自发辐射速率增加16.8%,最终使光子的总收集强度增加15.5%。

基于无微波金刚石NV色心测磁技术的电流测量应用

为了在特高压(UHV)环境下使用氮-空位(NV)色心量子测量技术,研究了金刚石主轴与磁场夹角对相应曲线及电流测量精度的影响。构建金刚石氮-空位七能级超精细结构模型,根据仿真结果得到不同磁场方向下最高灵敏度范围和最佳测量范围,从而确定探头的最佳放置角度。基于无微波金刚石氮-空位技术搭建了直流大电流测量实验平台,测试了100~5000A范围内荧光电压对电流的响应曲线。实验结果表明,该平台对5000A直流电流测量误差在0.25%以内。作为无源器件,无微波金刚石氮-空位色心测磁传感器全光纤信号传输具备良好耐压性能,同时可在室温下工作,并具有结构紧凑、灵敏度高、抗电磁干扰能力强等优势,适用于特高压环境下的直流电流测量,为传统电力行业检测提供了新的检测方法。

Micron-sized fiber diamond probe for quantum precision measurement of microwave magnetic field

We present a quantitative measurement of the horizontal component of the microwave magnetic field of a coplanar waveguide using a quantum diamond probe in fiber format.The measurement results are compared in detail with simulation,showing a good consistence.Further simulation shows fiber diamond probe brings negligible disturbance to the field under measurement compared to bulk diamond.This method will find important applications ranging from electromagnetic compatibility test and failure analysis of high frequency and high complexity integrated circuits.

High-resolution imaging of magnetic fields of banknote anti-counterfeiting strip using fiber diamond probe

Counterfeiting of modern banknotes poses a significant challenge,prompting the use of various preventive measures.One such measure is the magnetic anti-counterfeiting strip.However,due to its inherent weak magnetic properties,visualizing its magnetic distribution has been a longstanding challenge.In this work,we introduce an innovative method by using a fiber optic diamond probe,a highly sensitive quantum sensor designed specifically for detecting extremely weak magnetic fields.We employ this probe to achieve high-resolution imaging of the magnetic fields associated with the RMB 50denomination anti-counterfeiting strip.Additionally,we conduct computer simulations by using COMSOL Multiphysics software to deduce the potential geometric characteristics and material composition of the magnetic region within the anti-counterfeiting strip.The findings and method presented in this study hold broader significance,extending the RMB 50 denomination to various denominations of the Chinese currency and other items that employ magnetic anti-counterfeiting strips.These advances have the potential to significantly improve and promote security measures in order to prevent the banknotes from being counterfeited.

Insight into the nitrogen-vacancy center formation in type-Ib diamond by irradiation and annealing approach

Comprehending the microscopic formation of nitrogen vacancy(NV)centers in nitrogen-doped diamonds is crucial for enhancing the controllable preparation of NV centers and quantum applications.Irradiation followed by annealing simulations for a type-Ib diamond with a 900 ppm concentration of isolated nitrogen is conducted along different orientations and at different annealing temperatures.In these simulations,molecular dynamics(MD)with smoothly connected potential functions are implemented.MD simulations revealed the dynamic formation process of the NV center,which was subsequently verified by first-principles calculations and experiments.The results indicate that vacancies undergo one or multiple migrations by exchanging sites with neighboring atoms.There are three mechanisms for the formation of NV centers:direct irradiation-induced NV formation,irradiation with further annealing to form NV and vacancy migration(VM)during the annealing process.Furthermore,the results show that both VM and NV center formations are affected by orientations.This study clarifies the formation of NV centers across multiple scales and provides a solid foundation for the targeted preparation of NV centers.

基于深度学习的NV色心轴向快速识别

文章提出一种利用NV色心的角向偏振光成像图快速确定NV色心轴向的深度学习方法。NV色心的光致发光特性与排列在垂直于NV色心对称轴平面上的2个正交偶极子有关,利用角向偏振光可以得到NV轴对应的正交光学偶极子的成像图;通过数字仿真可以模拟不同NV轴向在角向偏振光作用下的成像图案,以此构建数据集并搭建神经网络进行学习;将神经网络模型作为NV成像图和其轴向之间的映射,从而根据给定的成像图直接得出NV色心的部分轴向值,再依据金刚石晶格中的角度约束关系,得到金刚石中NV色心的完整轴向。基于NV色心的角向偏振光成像图,在保证识别精度的前提下,实现对NV轴向的实时确定,提高以NV轴向为前置条件的各项工作(如磁场重构等)的效率。

基于金刚石NV色心的电流传感技术及其标准化研究初探

为推进量子化电流传感技术的落地应用,探讨了基于金刚石NV色心的电流传感技术,初步研究了其标准化技术。首先,介绍了金刚石NV色心的结构和物理特性,分析了基于金刚石NV色心的光学特性及自旋量子相干性的电流传感测量原理,研究了磁噪声抑制、磁测量灵敏度提升和测量芯片小型化等实用化技术;然后,分析了基于金刚石NV色心的电流传感测量技术的技术优势和标准化需求,提出了标准体系建设建议,为基于金刚石NV色心的电流传感技术研究、设备研制及传感测量系统落地应用提供技术支撑。

采用磁屏蔽环结构的金刚石NV色心全光直流互感器系统

针对目前电力系统对电流互感器的精度与灵敏度提出的更高要求,提出了一种基于金刚石氮-空位(NV)色心的全光直流互感器的系统方案,系统包括光源模块、激光反馈模块、激光分束模块、一次传感探头模块、激光分频模块、光电转换模块以及信号采集和数据处理模块。对系统中的磁屏蔽环进行了结构的设计与仿真,并对仿真结果进行了实验验证。最后搭建了单通道实验验证系统,系统实测结果表明,设计的全光直流互感器在5 000 A大电流下无磁屏蔽时可以达到0.35%的测量精度,加入磁屏蔽环后测量精度提升到了0.06%,从而为基于金刚石NV色心的全光直流互感器的研制提供了参考。

基于系综NV色心的温度传感器关键技术

金刚石中的氮空位中心（NV色心）具有独特的自旋特性,且其电子自旋受周围环境如温度的影响,从而可以通过探测NV色心的电子自旋态实现对温度的精密测量。在精密测量中,NV色心的哈密顿量起重要作用,而哈密顿量受周围环境温度的影响,所以研究了291-390 K温度下系综NV色心的光探测磁共振（ODMR）信号与温度的关系。随着温度的升高,零场劈裂D值逐渐减小,并且获得370-390 K时零场劈裂D值与温度间存在斜率为-61.65 kHz/K的线性关系,并对ODMR信号进行微波调制,这对以后实现高精度的温度场测量具有很好的应用前景,也为研究金刚石材料的温度特性提供了很好的技术支持。