金刚石氮-空位色心单电子自旋的电场驱动相干控制

金刚石氮-空位(nitrogen-vacancy,NV)色心量子体系因在室温条件下具有可实现单自旋寻址与操控、长量子相干时间等独特优势,在固态量子计算、量子精密测量等领域展现了巨大的应用潜力,其中单自旋的精确操控技术对于NV色心应用的发展尤为关键.NV色心量子体系中常用的自旋操控方法都是通过共振的交变磁场来驱动和操控NV色心电子自旋.本文开展了利用交变电场对NV色心电子自旋进行调控的技术研究.通过电极所产生的交变电场成功驱动了NV色心自旋在|ms=-1>与|ms=+1>两个△ms=±2的磁禁戒能级间的跃迁,并观测到受控自旋在相关能级的布居度周期性变化而展现出的Rabi振荡现象.进一步的研究表明,电场驱动Rabi振荡的频率受驱动电场功率的调控,与驱动电场的共振频率无直接关系.将自旋电控制技术与磁控制技术方法相结合,能够实现对NV色心3个自旋能级间直接跃迁的全操控.自旋电控制技术的发展将进一步推动NV色心量子体系在量子模拟、量子计算、电磁场的精密测量等领域研究和应用的发展.     

基于金刚石体系中氮-空位色心的固态量子传感

在室温下,金刚石中的氮-空位(NV)色心具有荧光强度稳定、电子自旋相干时间长以及与生俱来的原子尺寸的特点,是优良的纳米量子传感器.在成像领域中,将各种超分辨成像显微技术应用于NV色心体系,发展出多种高空间纳米分辨率的成像方法.此外,NV色心作为固态量子比特可以通过光学方法对其进行初始化和读取.NV色心电子自旋量子态还可以与电磁场、应力等进行相干耦合.基于这些耦合,科研人员在实验上实现了对相关物理量纳米级空间分辨率的高灵敏表征.目前这些量子传感技术可以应用在新材料、单个蛋白质核自旋、活体神经元等方面的测量中.本综述主要介绍金刚石中NV色心纳米量子传感器件的工作原理、实验实现和优化以及在相关领域的应用.     

基于金刚石氮-空位色心的温度传感

在各种物理量中,温度是最直观和最普遍的量.温度的剧烈变化通常意味着物体的物理性质出现波动,因此在各个领域中温度往往是重要的指标.随着科学技术的发展,许多领域研究和应用的尺度越来越小,然而在小于10μm的空间尺度内还没有通用的温度测量方法.除了空间分辨率的要求,传感器在测量过程中不应该对被测对象有巨大影响,金刚石氮-空位(nitrogen vacancy, NV)色心是一种稳定的发光缺陷,通过对其能谱和电子自旋量子态的测量,可以获得其附近温度、电磁场等物理量的信息.由于金刚石的化学特性稳定和热导率高,可以进行纳米尺度的非破坏性测量.它对细胞无毒,也可以用于生命领域的研究.此外,根据金刚石的特性, NV色心可以与光纤、扫描显微镜等技术结合,实现不同场景中的温度测量.本文将介绍金刚石NV色心的温度特性、测温原理及其在相关领域的应用.     

固态金刚石氮空位色心光学调控优化

在金刚石氮空位色心的高灵敏传感探测研究中,光学调控是氮空位色心实现高效光学初态制备及信息提取的关键.本文基于高浓度的金刚石氮空位色心系综检测展开,采用脉冲光学探测磁共振技术,系统地研究了激光初态极化时间、信息读取时间与激光功率的关联特性,并进一步研究了激光入射偏振角与传感信息精度的关系.探究了各个激光参数对高浓度金刚石氮空位色心系综[111]轴上光学探测磁共振谱中第一个共振峰的影响,并通过实验结果进行分析,最终选取在光功率密度为45.8 W/cm²下的最优实验参数(300μs的极化时间, 700 ns的读取时间,激光入射角为220°)进行了光学磁探测共振测试,与优化前的实验参数(极化时间为50μs,读取时间为3000 ns,入射角度为250°)相比,典型的磁检测灵敏度由21.6 nT/Hz1/2提升到5.6 nT/Hz1/2.以上研究结果表明我们已经实现光学精密调控的优化测量,这些研究结果也为高浓度氮空位色心系综精密调控实现温度和生物成像、量子计算及量子信息等领域调控传感检测提供了有效参考.     

金刚石氮空位色心体系的量子纠缠态制备

利用金刚石氮空位色心体系耦合于一个双边的光子晶体腔(该光子晶体腔与两个波导耦合)来制备Bell态、GHZ态和团簇态。当光子被探测和进行幺正操作后,就得到纠缠态。同时计算了该体系的保真度,发现在近似参数条件下,该模型可得到较好结果。     

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.     

金刚石中氮空位中心在外加磁场下的电子自旋共振

金刚石中单个氮空位中心的电子自旋在激光辐射下能够发出近红外的光致荧光,增加微波辐射可以对其进行量子调控,是室温条件下实现量子计算机的主要介质之一.本文利用激光共聚焦扫描显微系统观测到了金刚石晶体中氮空位中心的荧光二维扫描图,并通过二次相关函数测量验证了氮空位中心是单光子源.改变微波辐射频率得到了电子自旋共振谱,从而实现了对单个氮空位中心的量子调控.利用设计的可控静磁场研究了氮空位中心在不同磁场方向和大小时的光致荧光特性和自旋共振峰.实验结果表明两个电子自旋共振峰间的频率间距与静磁场的旋转角度成余弦函数关系,与理论分析结果一致.     

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.     

金刚石氮-空位色心温度测量激发激光误差抑制

基于金刚石氮-空位(NV)色心的温度传感技术,通过测量其基态子级之间的零场劈裂值(D)来实现对温度的感测。由于金刚石稳定性高,抗干扰能力强,可制成不同尺寸,NV色心测温方法被视为解决微纳米尺度温度高精度测量难题的一种重要技术途径,具有良好的应用前景。实验测量中,首先使用激光对色心进行电子自旋极化,然后使用微波对电子自旋进行调控,进而探测电子跃迁发出的荧光得到光学探测磁共振(ODMR)光谱,对谱线进行拟合分析获得D值。激光功率波动是重要的实验噪声来源之一,为了获得较高的极化率,需要足够的激光功率,然而较大激光功率下,光功率波动会影响电子自旋极化率,从而降低电子跃迁所发出荧光强度的稳定性,增加光谱的噪声,最终增大数据测量的误差。在常规测量中,不使用任何归一化参考的直接拟合法会将激光功率的波动直接反映在ODMR光谱上。为降低激光功率波动产生的误差,提出了一种特定编码的脉冲序列测量方法,可以在实验过程中获得不受微波调控的光子数参考值,对所探测的受到微波调控的光子数相对于参考值做归一化,从而输出归一化光谱。在实验室搭建的ODMR测量系统上开展了控温300 K的对比实验,考虑对脉冲编码序列两个时间...     

Electron spin resonance detection and identification of nitrogen centers in nanodiamonds

Individual nitrogen centers N⁰ and nitrogen pairs N ₂ ⁺ have been detected and identified in natural diamond nanocrystals by means of the high-frequency electron spin resonance method. The N⁰ nitrogen centers have been observed in synthetic diamond nanocrystallites with a size of less than 10 nm produced by high-temperature high-pressure sintering of detonation nanodiamonds. Thus, the possibility of the stable state of impurity nitrogen atoms in diamond nanoparticles has been demonstrated.     

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.     

电子自旋共振扫描隧道显微镜

单电子自旋极有可能发展成为未来信息学的基础。以电子自旋为核心的新型单分子或单原子器件将最终成为基本信息单元,基于单电子的自旋态将有可能构筑未来量子计算机的量子比特。但是,如何实现对单个电子自旋及其相干态和纠缠态的测量和控制,目前仍然是一个很大的挑战。作为调控单个电子自旋的重要实验手段,电子自旋共振扫描隧道显微镜的发展一直备受关注。文章简要介绍了电子自旋共振扫描隧道显微镜的基本概念,阐述了其发展历史和最新进展,归纳了机理探索的研究成果,论述了该设备研发面临的挑战与对策,并对未来的发展和应用做了展望。     

Enhancement of single‑photon emission from nitrogen‑vacancy centers with TiN/(Al,Sc)N hyperbolic metamaterial

The broadband enhancement of single‑photon emission from nitrogen‐vacancy centers in nanodiamonds coupled to a planar multilayer metamaterial with hyperbolic dispersion is studied experimentally. The metamaterial is fabricated as an epitaxial metal/dielectric superlattice consisting of CMOS‐compatible ceramics: titanium nitride (TiN) and aluminum scandium nitride (Al_xSc_1‐xN). It is demonstrated that employing the metamaterial results in significant enhancement of collected single‑photon emission and reduction of the excited‐state lifetime. Our results could have an impact on future CMOS‐compatible integrated quantum sources.

     

Electron spin resonance-scanning tunneling microscopy

Electron spin resonance-scanning tunneling microscopy (ESR-STM) is a rapidly developing surface-science technique that is sensitive to a single spin existing on or nearby a solid surface. The single spin is detected through elevated noise at the Larmor frequency that appears when the single spin participates in the tunneling process between the tip and the surface. In this review, experimental and theoretical works which have been performed up to date on ESR-STM are reviewed. The remaining experimental problems which have to be solved, possible approaches to differentiate between different mechanisms and the future of ESR-STM are discussed.\ PACS: 72.25.Dc Spin polarized transport in semiconductors, 72.70.+m Noise processes and phenomena, 73.20.Hb Impurity and defect levels; energy states of adsorbed species, 73.40.Gk Tunneling, 75.70.Rf Surface magnetism, 75.76.+j Spin transport effects, 76.30.-v Electron paramagnetic resonance and relaxation, 78.47.-p Spectroscopy of solid state dynamics     

Energetics of carbon and nitrogen impurities and their interactions with vacancy in vanadium

We studied the energetic behaviors of interstitial and substitution carbon(C)/nitrogen(N) impurities as well as their interactions with the vacancy in vanadium by first-principles simulations. Both C and N impurities prefer the octahedral site(O-site). N exhibits a lower formation energy than C. Due to the hybridization between vanadium-d and N/C-p, the N-p states are located at the energy from-6.00 e V to-5.00 e V, which is much deeper than that from-5.00 e V to-3.00 e V for the C-p states. Two impurities in bulk vanadium, C–C, C–N, and N–N can be paired up at the two neighboring Osites along the 111 direction and the binding energies of the pairs are 0.227 e V, 0.162 e V, and 0.201 e V, respectively.Further, we find that both C and N do not prefer to stay at the vacancy center and its vicinity, but occupy the O-site off the vacancy in the interstitial lattice in vanadium. The possible physical mechanism is that C/N in the O-site tends to form a carbide/nitride-like structure with its neighboring vanadium atoms, leading to the formation of the strong C/N–vanadium bonding containing a covalent component.     

Preparation of spin squeezed state in SiV centers coupled by diamond waveguide

Spin squeezing is a fascinating manifestation of many-particle entanglement and one of the most promising quantum resources. In this paper, we propose a novel realization of a solid-state quantum spin squeezing by applying Si V centers embedded in a diamond waveguide with the help of a microwave field. The phenomena about the generation of spin squeezing are analyzed numerically in Markovian environments. Our analysis shows that spin squeezing can be generated with the microwave field's help under some realistic conditions, despite the presence of dephasing and mechanical damping.This solid-state spin squeezing based on Si V centers in diamonds might be applied to magnetometers, interferometry, and other precise measurements.     

Electron paramagnetic resonance detection of the giant concentration of nitrogen vacancy defects in sintered detonation nanodiamonds

A giant concentration of nitrogen vacancy defects has been revealed by the electron paramagnetic resonance (EPR) method in a detonation nanodiamond sintered at high pressure and temperature. A high coherence of the electron spins at room temperature has been observed and the angular dependences of the EPR spectra indicate the complete orientation of the diamond system.     

氮掺杂和空位对石墨烯纳米带热导率影响的分子动力学模拟

石墨烯是近年纳米材料研究领域的一个热点,其独特的热学性质受到了广泛关注,为了实现对石墨烯传热特性的预期与可控,利用氮掺杂和空位缺陷对石墨烯进行改性.采用非平衡态分子动力学方法研究了扶手形石墨烯纳米带中氮掺杂浓度、位置及空位缺陷对热导率影响并从理论上分析了热导率变化原因.研究表明氮掺杂后石墨烯纳米带热导率急剧下降,氮浓度达到30%时,热导率下降了75.8%;氮掺杂位置从冷浴向热浴移动过程中,热导率先近似的呈线性下降后上升;同时发现单原子三角形氮掺杂结构比多原子平行氮掺杂结构对热传递抑制作用强;空位缺陷的存在降低了石墨烯纳米带热导率,空位缺陷位置从冷浴向热浴移动过程中,热导率先下降后上升,空位缺陷距离冷浴边缘长度相对于整个石墨烯纳米带长度的3/10时,热导率达到最小.石墨烯纳米带热导率降低的原因主要源于结构中声子平均自由程和声子移动速度随着氮掺杂浓度、位置及空位缺陷位置的改变发生了明显变化.这些结果有利于纳米尺度下对石墨烯传热过程进行调控及为新材料的合成应用提供了理论支持.     

Electron spin polarisation in the photoreduction of xanthone in alcohol: effect of concentration and temperature

Time-resolved EPR studies of the hydrogen abstraction reaction of photoexcited xanthone in 2-propanol were carried out as a function of the concentration of xanthone and the sample temperature. The temperature was varied from 22°C to about ?30°C, and the concentration from about 0.2 to 4.0?mM. At low temperature or concentration, the observed spectra of the xanthone ketyl radical and the propan-2-olyl radical could be simulated as a superposition of a hyperfine-independent component due to the emissive triplet mechanism and a hyperfine-dependent component due to the S–T₀ radical pair mechanism. However, with an increase in the concentration of xanthone, the relative contribution of TM decreases, and, concomitantly, the net absorptive component of only the xanthone ketyl radical increases. As the spin polarisation mechanisms do not predict any concentration dependence, this unusual behaviour is explained by invoking the enhancement of the spin–lattice relaxation rates due to Heisenberg spin exchange occurring at high local concentrations of the radicals. The net absorptive signal is attributed to thermally equilibrated radicals. The observed temperature dependence of the spin polarisation behaviour is similarly explained. The origin of the net absorptive signal in the TREPR spectra of the acetone?2-propanol system is also attributed to thermally equilibrated radicals. The self-quenching mechanism of xanthone is proposed to be an electron-transfer reaction from an excited xanthone molecule to another xanthone in the ground state.