基于金刚石色心自旋磁共振效应的微位移测量方法

基于压电陶瓷精密微位移系统的扫描探测技术是目前精密测量仪器进行微纳区域/结构性能测试的核心系统,但压电陶瓷材料存在迟滞、非线性问题,限制了对微位移分辨能力的提升.本文以金刚石氮空位色心为敏感单元,利用电子自旋效应对磁场强度的高分辨敏感机理,结合永磁体周围不同位置对应的磁场强度变化关系,提出了一种基于金刚石氮空位色心电子自旋敏感机理的微位移检测方法.通过建立电子自旋效应与微位移的关联模型,搭建了相应的微位移测量系统.经实验验证,该系统对微位移测试的灵敏度为16.67 V/mm,检测分辨率达到60 nm,实现了对微位移的高分辨率测量.并通过理论分析,该系统的微位移测量分辨率可进一步提升至亚纳米级水平,为新型微位移测量技术提供了发展方向和研究思路.     

基于金刚石NV色心的纳米尺度磁场测量和成像技术

纳米级分辨率的磁场测量和成像是磁学中的一种重要研究手段.金刚石中的单个氮-空位点缺陷电子自旋作为一种量子传感器,具有灵敏度高、原子级别尺寸、可工作在室温等诸多优势,灵敏度可以达到单核自旋级别,空间分辨率达到亚纳米.将这种磁测量技术与扫描成像技术结合,能够实现高灵敏度和高分辨率的磁场成像,定量地重构出杂散场.这种新型的磁成像技术可以给出磁学中多种重要的研究对象如磁畴壁、反铁磁序、磁性斯格明子的结构信息.随着技术的发展,基于氮-空位点缺陷的磁成像技术有望成为磁性材料研究的重要手段.     

金刚石氮空位色心耦合机械振子和腔场系统中方差压缩研究

研究了金刚石氮空位中心(NV色心)同时耦合腔场和机械振子系统中声子场的方差压缩动力学特性,分析了金刚石NV色心初态和NV色心与机械振子耦合强度对声子场方差压缩影响.结果发现:可以制备压缩时间长、压缩幅度大的声子场压缩态,其物理原因是机械振子具有最大相干性,并且通过调控NV色心初态以及磁场梯度可以实现对机械振子方差压缩非经典特性的操控,从而在理论上提供了一种调控声子场方差压缩的方式.     

Reconstruction of vector static magnetic field by different axial NV centers using continuous wave optically detected magnetic resonance in diamond

We carried out a proof-of-principle demonstration of the reconstruction of a static vector magnetic field involving adjacent three nitrogen-vacancy(NV) sensors with corresponding different NV symmetry axes in a bulk diamond. By means of optical detection of the magnetic resonance(ODMR) techniques, our experiment employs the continuous wave(CW) to monitor resonance frequencies and it extracts the information of the detected field strength and polar angles with respect to each NV frame of reference. Finally, the detected magnetic field relative to a fixed laboratory reference frame was reconstructed from the information acquired by the multi-NV sensor.     

Quantum information processing and metrology with color centers in diamonds

The Nitrogen Vacancy （NV） center is becoming a promising qubit for quantum information processing. The defect has a long coherence time at room temperature and it allows spin state initialized and read out by laser and manipulated by microwave pulses. It has been utilized as a ultra sensi- tive probe for magnetic fields and remote spins as well. Here, we review the recent progresses in experimental demonstrations based on NV centers. We first introduce our work on implementation of the Deutsch- Jozsa algorithm with a single electronic spin in diamond. Then the quantum nature of the bath around the center spin is revealed and continuous wave dynamical decoupling has been demonstrated. By applying dynamical decoupling, a multi-pass quantum metrology protocol is realized to enhance phase estimation. In the final, we demonstrated NV center can be regarded as a ultra-sensitive sensor spin to implement nuclear magnetic resonance （NMR） imaging at nanoscale.     

基于金刚石氮-空位色心自旋系综与超导量子电路混合系统的量子节点纠缠

量子纠缠是实现量子计算和量子通信的核心基础,本文提出了在金刚石氮-空位色心(NV centers)自旋系综与超导量子电路耦合的混合系统中实现两个分离量子节点之间纠缠的理论方案.在该混合系统中,把金刚石NV centers自旋系综和与之耦合的超导共面谐振器视为一个量子节点,两个量子节点之间通过一个空的超导共面谐振器连接.具有较长相干时间的NV centers自旋系综作为一个量子存储器,用于制备、存储和发送量子信息;易于外部操控的超导量子电路可执行量子逻辑门操作,快速调控量子信息.为了实现两个分离量子节点之间的纠缠,首先对系统的哈密顿量进行正则变换,将其等价为两个NV centers自旋系综与同一个超导共面谐振器之间的JC耦合;然后采用NV centers自旋-光子混合比特编码的方式,通过调节超导共面谐振器的谐振频率,精确控制体系演化时间,高保真度地实现了两个分离量子节点之间的量子纠缠.本方案还可以进一步扩展和集成,用于构建多节点纠缠的分布式量子网络.     

利用金刚石氮-空位色心精确测量弱磁场的探索

基于金刚石氮-空位色心对精确测量微弱静磁场进行了探索.金刚石氮-空位色心电子自旋的退相干时间高度依赖于外磁场,而不同的退相干特征时间对磁场的灵敏度不同.对金刚石氮-空位色心电子自旋在不同强度外磁场下的退相干过程进行模拟,得到不同退相干特征时间与磁场大小的高准确度关系,提出了基于响应度最高的退相干特征时间测量静态弱磁场大小和方向的方法,并分析了该方法测量静态弱磁场的灵敏度,证明该方法的测量灵敏度比一般磁场测量仪器更高.     

基于金刚石氮-空位色心的精密磁测量

磁是一种重要的物理现象,对其进行精密测量推动了许多科技领域的发展.各类测磁技术,包括霍尔传感器、超导量子干涉仪、自旋磁共振等,都致力于提升空间分辨率和灵敏度.近年来,金刚石中的氮-空位色心广受关注.这一固态单自旋体系具有许多优点,例如易于初始化和读出、可操控、具有较长相干时间等,这使得它不仅在量子信息、量子计算等领域崭露头角,而且在量子精密测量上显现出巨大的应用前景.基于氮-空位色心,利用动力学解耦、关联谱等技术,已实现若干高灵敏度、高分辨率的微观磁共振实验,其中包括纳米尺度乃至单分子、单自旋的核磁共振和电子顺磁共振.氮-空位色心也可以用于微波和射频信号的精密测量.本文对围绕上述主题开展的一系列研究工作进行综述.     

Sub-optical resolution of single spins using magnetic resonance imaging at room temperature in diamond

There has been much recent interest in extending the technique of magnetic resonance imaging (MRI) down to the level of single spins with sub-optical wavelength resolution. However, the signal to noise ratio for images of individual spins is usually low and this necessitates long acquisition times and low temperatures to achieve high resolution. An exception to this is the nitrogen-vacancy (NV) color center in diamond whose spin state can be detected optically at room temperature. Here we apply MRI to magnetically equivalent NV spins and demonstrate fully resolved spectra with resolution well below the optical wavelength of the readout light. In addition, using a microwave version of MRI we achieved a resolution that is 1/270 in size of the coplanar striplines, which define the effective wavelength of the microwaves that were used to excite the transition. This technique can eventually be extended to imaging of large numbers of NVs in a confocal spot and possibly to image nearby dark spins via their mutual magnetic interaction with the NV spin.     

Room-Temperature Level Anticrossing and Cross-Relaxation Spectroscopy of Spin Color Centers in SiC Single Crystals and Nanostructures

A sharp variation of the near infrared photoluminescence intensity for spin-3/2 color centers in hexagonal (4H-, 6H-) and rhombic (15R-) SiC polytypes in the vicinity of level anticrossing (LAC) and cross-relaxation in an external magnetic field at room temperature are observed. This effect can be used for a purely all-optical sensing of the magnetic field with nanoscale spatial resolution. A distinctive feature of the LAC signal is a weak dependence on the magnetic field direction that allows monitoring of the LAC signals in the nonoriented systems, such as powder materials, without need to determine the nanocrystal orientation in the sensing measurements. Furthermore, an LAC-like signal is also observed for the spin color centers (NV centers) in diamond in low magnetic fields with only marginal dependence on the magnetic field direction. This effect is enabled to detect weak magnetic fields using nanodiamond samples in the form of disordered mixture. In addition, the optically detected magnetic resonance and LAC techniques are suggested to serve as a simple method to determine the local stress in nanodiamonds under ambient conditions.     

Microwave Antenna for Exciting Optically Detected Magnetic Resonance in Diamond NV Centers

A microwave antenna configuration shaped as coaxial resonant coils is proposed for exciting magnetic dipole transitions of the optical ground state of the nitrogen—vacancy color center in diamond. The field within the antenna is simulated, field amplitudes are experimentally measured.     

Second-order magnetic field gradient-induced strong coupling between nitrogen-vacancy centers and a mechanical oscillator

We consider a cantilever mechanical oscillator (MO) made of diamond. A nitrogen-vacancy (NV) center lies at the end of the cantilever. Two magnetic tips near the NV center induce a strong second-order magnetic field gradient. Under coherent driving of the MO, we find that the coupling between the MO and the NV center is greatly enhanced. We studied how to generate entanglement between the MO and the NV center and realize quantum state transfer between them. We also propose a scheme to generate two-mode squeezing between different MO modes by coupling them to the same NV center. The decoherence and dissipation effects for both the MO and the NV center are numerically calculated using the present parameter values of the experimental configuration. We have achieved high fidelity for entanglement generation, quantum state transfer, and large two-mode squeezing.     

Nanoscale detection of faint machinery vibration using the NV center in diamond

We propose a novel method for detection of the faint machinery vibration at the nanometer resolution based on the spin magnetic resonant effect. A suspension magnet acts as a vibration sensor to transfer the vibration signals as the magnetic field fluctuation to excite the spin magnetic resonance. Due to the high sensitivity of the magnetic field of the nitrogen-vacancy center in diamond, the theoretical detection limit of mechanical vibration is as high as 5.7 nm, and the actual measurement resolution reached 12.8 nm, and proved the potential for further improvement to ∼pm resolution. The feasibility of this method is verified by dynamic tests. This method provides a novel approach for the detection of micro-mechanical vibrations.     

Creation of entangled state between two spaced NV centers in diamond

A method for creating an entangled state between two NV centers in a diamond that do not interact directly with each other is studied. The method is based on the excitation of centers via a half divider (a 50% beamsplitter) with the subsequent coherent inversion of the spin of the excited center and the detection of a photon emitted by the excited center. The parameters of a multimode single-photon pulse that make it possible to achieve a maximally possible excitation of the centers at a given solid angle of the focusing of the light on the center are found. The probability to create an entangled state in relation to the parameters of the initial state of a photon, the turn-on and turn-off times of the microwave pulse and the light focusing solid angle is determined. Optimal values of these parameters that ensure a maximal probability of the entanglement creation are determined.     

Online optimization for optical readout of a single electron spin in diamond

The nitrogen-vacancy (NV) center in diamond has been developed as a promising platform for quantum sensing, especially for magnetic field measurements in the nano-tesla range with a nano-meter resolution. Optical spin readout performance has a direct effect on the signal-to-noise ratio (SNR) of experiments. In this work, we introduce an online optimization method to customize the laser waveform for readout. Both simulations and experiments reveal that our new scheme optimizes the optically detected magnetic resonance in NV center. The SNR of optical spin readout has been witnessed a 44.1% increase in experiments. In addition, we applied the scheme to the Rabi oscillation experiment, which shows an improvement of 46.0% in contrast and a reduction of 12.1% in mean deviation compared to traditional constant laser power SNR optimization. This scheme is promising to improve sensitivities for a wide range of NV-based applications in the future.     

Proposed spin amplification for magnetic sensors employing crystal defects

Recently there have been several theoretical and experimental studies of the prospects for magnetic field sensors based on crystal defects, especially nitrogen vacancy (NV) centers in diamond. Such systems could potentially be incorporated into an atomic force microscopy-like apparatus in order to map the magnetic properties of a surface at the single spin level. In this Letter we propose an augmented sensor consisting of an NV center for readout and an "amplifier" spin system that directly senses the local magnetic field. Our calculations show that this hybrid structure has the potential to detect magnetic moments with a sensitivity and spatial resolution far beyond that of a simple NV center, and indeed this may be the physical limit for sensors of this class.     

Towards T 1-limited magnetic resonance imaging using Rabi beats

Two proof-of-principle experiments toward T ₁-limited magnetic resonance imaging with NV centers in diamond are demonstrated. First, a large number of Rabi oscillations is measured and it is demonstrated that the hyperfine interaction due to the NV??s ¹⁴N can be extracted from the beating oscillations. Second, the Rabi beats under V-type microwave excitation of the three hyperfine manifolds is studied experimentally and described theoretically.     

Temperature-scanned magnetic resonance and the evidence of two-way transfer of a nitrogen nuclear spin hyperfine interaction in coupled NV-N pairs in diamond

New method for the detection of magnetic resonance signals versus temperature is developed on the basis of the temperature dependence of the spin Hamiltonian parameters of the paramagnetic system under investigation. The implementation of this technique is demonstrated on the nitrogen-vacancy (NV) centers in diamonds. Single NV defects and their ensembles are suggested to be almost inertialess temperature sensors. The hyperfine structure of the ¹⁴N nitrogen nuclei of the nitrogen-vacancy center appears to be resolved in the hyperfine structure characteristic of the hyperfine interaction between NV and an N _s center (substitutional nitrogen impurity) in the optically detected magnetic resonance spectra of the molecular NV-N _s complex. Thus, we show that a direct evidence of the two-way transfer of a nitrogen nuclear spin hyperfine interaction in coupled NV-N _s pairs was observed. It is shown that more than 3-fold enhancement of the NV optically detected magnetic resonance signal can be achieved by using water as a collection optics medium.     

A novel demodulation method for transmission using nitrogen-vacancy-based solid-state quantum sensor

Diamond based quantum sensing is a fast-emerging field with both scientific and technological significance. The nitrogen-vacancy (NV) center, a crystal defect in diamond, has become a unique object for microwave sensing applications due to its excellent stability, long spin coherence time, and optical properties at ambient condition. In this work, we use diamond NV center as atomic receiver to demodulate on-off keying (OOK) signal transmitted in broad frequency range (2 GHz-14 GHz in a portable benchtop setup). We proposed a unique algorithm of voltage discrimination and demonstrated audio signal transceiving with fidelity above 99%. This diamond receiver is attached to the end of a tapered fiber, having all optic nature, which will find important applications in data transmission tasks under extreme conditions such as strong electromagnetic interference, high temperatures, and high corrosion.     

Bistability and steady-state spin squeezing in diamond nanostructures controlled by a nanomechanical resonator

As the quantum states of nitrogen vacancy (NV) center can be coherently manipulated and obtained at room temperature, it is important to generate steady-state spin squeezing in spin qubits associated with NV impurities in diamond. With this task we consider a new type of a hybrid magneto-nano-electromechanical resonator, the functionality of which is based on a magnetic-field induced deflection of an appropriate cantilever that oscillates between NV spins in diamond. We show that there is bistability and spin squeezing state due to the presence of the microwave field, despite the damping from mechanical damping. Moreover, we find that bistability and spin squeezing can be controlled by the microwave field and the parameter V_z$V_z$. Our scheme may have the potential application on spin clocks, magnetometers, and other measurements based on spin–spin system in diamond nanostructures.