Effect of the Variable B-Field on the Dynamic of a Central Electron Spin Coupled to an Anti-Ferromagnetic Qubit Bath

This present issue is an extension of the work of Y. Xiao-Zhong et al. who investigated the influence of constant external magnetic field on the decoherence of a central electron spin of atom coupled to an anti-ferromagnetic environment. We have shown in this work that the character variability of the field induces oscillations amongst the eigen modes of the environment. This observation is made via the derivation of the transition probability density of state, a manner by which critical parameters (parameters where transition occur) of the system could be obtained as it shows resonance peak. We equally observed that the two different magnons modes resulting from the frequency splitting via the application of the time-varying external B-Field, exhibit each a resonant peak of similar amplitude at different temperature ranges. This additional information shows that the probability for the central spin system to remain in its initially prepared diabatic state is enhanced for some temperature ranges for the corresponding two magnon modes. Hence, these temperature ranges where the probability density is maximum could save as decoherence free environment;an important requirement for the implementation of quantum computation and information processing in solid state circuitry. The theoretical and numerical results presented for the decoherence time and the probability density are that of a decohered central electron spin coupled to an anti-ferromagnetic spin bath. The theory is based on a spin wave approximation and on the density matrix using both transformations of Bloch, Primakov and Bogoliobuv in the adiabatic limit.

Spin fluctuations and unconventional superconducting pairing in iron-based superconductors

In this article, we review the recent theoretical works on the spin fluctuations and superconductivity in iron-based superconductors. Using the fluctuation exchange approximation and multi-orbital tight-binding models, we study the char- acteristics of the spin fluctuations and the symmetries of the superconducting gaps for different iron-based superconductors. We explore the systems with both electron-like and hole-like Fermi surfaces （FS） and the systems with only the electron-like FS. We argue that the spin-fluctuation theories are successful in explaining at least the essential part of the problems, indicating that the spin fluctuation is the common origin of superconductivity in iron-based superconductors.

The c—Axis Infrared Conductivity of a dx^2—y^2— Wave Superconductor with the Hopping Assisted by the Spin Fluctuations

A theory of the c-axis infrared conductivity of a dx2-y2-wave superconductor due to the competition between the interlayer direct hopping and the hopping assisted by the spin fluctuations has been developed. The prediction of our theory captures the main feature of the experiment. Thus we argue that the anomalous behavior of the c-axis infrared conductivity of the underdoped cuprates in superconducting state may be properly understood within the theory.

Exploring charge and spin fluctuations in infinite-layer cuprate SrCuO_(2)from a phonon perspective

The infinite-layer cuprate ACu O_(2)(A=Ca,Sr,Ba)possesses the simplest crystal structure among numerous cuprate superconductors and can serve as a prototypical system to explore the unconventional superconductivity.Based on the first-principles electronic structure calculations,we have studied the electronic and magnetic properties of the infinite-layer cuprate SrCuO_(2)from a phonon perspective.We find that interesting fluctuations of charges,electrical dipoles,and local magnetic moments can be induced by the atomic displacements of phonon modes in SrCuO_(2)upon the hole doping.Among all optical phonon modes of SrCuO_(2)in the antiferromagnetic Néel state,only the A_(1g)mode that involves the full-breathing O vibrations along the Cu-O bonds can cause significant fluctuations of local magnetic moments on O atoms and dramatic charge redistributions between Cu and O atoms.Notably,due to the atomic displacements of the A_(1g)mode,both the charge fluctuations on Cu and the electrical dipoles on O show a dome-like evolution with increasing hole doping,quite similar to the experimentally observed behavior of the superconducting T_(c);in comparison,the fluctuations of local magnetic moments on O display a monotonic enhancement along with the hole doping.Further analyses indicate that around the optimal doping,there exists a large softening in the frequency of the A_(1g)phonon mode and a van Hove singularity in the electronic structure close to the Fermi level,suggesting potential electron-phonon coupling.Our work reveals the important role of the full-breathing O phonon mode playing in the infinite-layer SrCuO_(2),which may provide new insights in understanding the cuprate superconductivity.

Effects of exchange interaction and spin-fluctuation on the magnetic and magneto-optic properties of NdF_3

The exchange interaction between the electrons in the different magnetic ions and the spin-fluctuation of the magnetic ions exist in the paramagnetic media NdF3. The exchange interaction between the electrons in the different magnetic ions may be equivalent to an effective field Hin that is in direct proportion to the magnetization M. The spin-fluctuation of the magnetic ions leads the coefficient of the effective field to vary with temperature. The effective field is given as Hin = -（0.75 ＋ 0.22T） × 10^-5M in NdF3. When the secondary crystal field effect is taken into account, the magnetic susceptibility and Verdet constant are calculated for NdF3 by means of the effective field Hin and the applied field He. The calculated results are in agreement with the measured ones.

Particle–hole fluctuations and possible superconductivity in doped α-RuCl_3

We study various particle–hole excitations and possible superconducting pairings mediated by these fluctuations in doped α-RuCl_3 by using multi-band Hubbard model with all t_(2g) orbitals. By performing a random-phase-approximation(RPA) analysis, we find that among all particle–hole excitations, the j_(eff)= 1/2 pseudospin fluctuations are dominant, suggesting the robustness of j_(eff)= 1/2 picture even in the doped systems. We also find that the most favorable superconducting state has a d-wave pairing symmetry.

聚酯熔体黏度的调控及对直纺涤纶长丝品质的影响

当聚合熔体黏度超出控制范围时,会影响涤纶长丝的生产状况,造成飘丝、断头多等问题,产品线密度、断裂强度、断裂伸长率的变异系数都会上升,影响后道加弹生产情况并造成产品性能指标的下降。分析了聚酯生产过程中催化剂浓度、缩聚反应温度、缩聚真空度、停留时间、终缩聚釜搅拌器转速等对熔体黏度的影响,得出如下结论:熔体在线黏度需根据工艺参数调节,使产品黏度控制在规定范围内,保证产品生产过程的稳定性。

基于特征空间变换的纺纱过程多关联参数质量波动异常检测

纺纱过程参数众多且相互关联,模糊了过程参数与纱线质量指标间的重要信息,针对纺纱过程参数强耦合带来的纺纱过程质量波动难以检测与控制的问题,提出一种基于特征空间变换的纺纱过程多关联参数质量波动异常检测方法。首先,分析纺纱过程参数间的关联关系,采用偏最小二乘法(PLS)消除参数之间的相关性,获得具有正交性的特征空间。然后,利用新的特征空间数据计算局部离群因子(LOF)统计量,判定纺纱过程是否稳定,定位异常波动区域。最后将相关性分析后的异常波动数据作为深度置信网络(DBN)模型的输入,识别纺纱过程异常波动类型。通过算例进行验证,结果显示所提模型将纺纱过程多关联参数异常检测精度提高到98.2%。

基于窗口波动模式识别的纺纱过程质量波动异常预警

纺纱过程受到多因素的影响,其质量波动呈现复杂性。文章针对纺纱过程质量波动异常难以及时预警的问题,提出一种基于窗口波动模式识别的纺纱过程质量波动异常预警方法。首先对纺纱过程参数时序集进行窗口分解,定义异常波动率对窗口序列的波动程度进行表征;然后根据窗口是否存在异常预期信号对模式进行判别,并构建参数优化的随机森林模型对窗口波动模式进行识别,据此构建纺纱过程质量波动异常预警策略。通过细纱过程数据集进行验证,结果显示所提方法在实现对纺纱质量异常波动进行预警的同时还能够准确追溯异常波动源头,为纺纱生产质量稳定提供保证。

市场动力学原理——经济动力学与标准模型(Ⅱ)

市场动力学以经典电动力学为基础,以量子电动力学为参考模型框架,其构造自始至终贯穿布尔巴基结构主义思想。市场动力学研究价格、需求和供给三者之间的相互作用,量子电动力学研究光子、电子和正电子三者之间的相互作用;两者都属于单荷动力学范畴,共享U(1)对称群。市场动力学引入了市场荷,并以此分别定义了需求与供给。通过考察市场犹豫现象,为需求和供给引入自旋作为其内禀性质。于是,需求与供给可由狄拉克旋量定义。通过引入钱锥和价壳,定义了虚价格;需求与供给通过交换虚价格而相互作用。这些相互作用可为费曼图所刻画。认知场具有极化决策的功能,由磁场所刻画。市场动力学认为,社会经济本身是一个实验,每个市场参与者都是观测者。我们建立了市场观测的非对易关系以及观测信息的市场版测不准原理,并以此定义了量子版看不见的手。在经典电动力学的基础上,讨论了价格场与麦克斯韦场的关系,并引入了规范势的概念。高阶认知(包括博弈、决策与推理)引起的市场涨落(包括介观与量子涨落)。各种市场内在的涨落现象既是理解市场参与者认知又是理解市场相变的基础。定义了市场波函数的六个组分,即全局相因子,全局规范势与全局规范场强,以及局域相因子,局域规范势与局域规范场强。规范变换是量子电动力学和市场动力学的精彩部分,随后给出规范原理,说明全局对称性是局域对称性的必要条件。引入了四个算子,即牛顿均值算子、爱因斯坦钱锥算子、薛定谔演化算子和狄拉克场论算子,将这四个算子分别施用于市场波函数,呈现市场波函数的四种算子相态;算子态的改变,称为市场波函数的相变。

High-T_c superconductivity in FeSe at high pressure:Dominant hole carriers and enhanced spin fluctuations

With the support by the National Natural Science Foundation of China and the Ministry of Science and Technology of China,a collaborative study led by Prof.Cheng Jinguang(程金光)from the Institute of Physics,Chinese Academy of Sciences found evidence for the presence of hole pockets and the enhanced spin fluctuations in the pressure-induced high-Tcsuperconductivity phase of FeSe,which was published

基于改进神经网络的降低锭子转速波动控制算法

针对细纱在电锭细纱机上卷绕过程中易出现断头的问题,在不升级电锭细纱机设备的前提下,提出一种改进的神经网络在线实时整定锭子转速PID控制算法。对于神经网络的缺陷,引入粒子群优化(particle swarm optimization,PSO)算法,使电锭细纱机锭子运行过程中转速和转矩波动更小,更好地应对某处纱线张力波动较大的扰动响应。通过搭建实验平台,验证了锭子无刷直流电机优化后的算法相较于经典PID算法,转速波动降低了2.08%,转矩波动降低了8.3%,从而减少了细纱卷绕过程中断头的产生。该方法可应用在细纱产量和质量的优化领域。

新几何阻挫物质M_2(OH)_3X的新颖量子磁性———磁有序和涨落在均匀自旋系的共存

几何阻挫引起诸多的未知新颖量子状态,这些新颖量子相的理解预计将带来物理学的突破。笔者通过材料科学研究,偶然发现了新型几何阻挫系列M2(OH)3X[M=Cu,Co,Ni,Mn,Fe etc.;X=Cl,Br,I]。它们初步展示了新颖的磁性,虽然这些物质是由单一磁性离子组成的均匀晶体,在这些化学均匀系中自旋的有序[如铁磁或反铁磁秩序]和自旋涨落同时共存。因为d电子磁性离子的量子性,本物质系列提供了研究几何阻挫引发的新颖量子特性的绝好舞台。本文综合介绍我们在这一方面最近取得的主要成果。他山之石可以攻玉,新材料的发现往往会带来物理学的新进展,本文同时也例证了材料科学对凝聚态物理的重要性。

铁磁体中磁振子的压缩态

研究了铁磁体中磁振子的压缩态.采用霍尔斯坦和普里马科夫提出的二次量子化方法把磁振子系统的哈密顿量简化,并应用平均场理论处理了哈密顿量中的非线性相互作用项;通过计算自旋涨落的平均值得到了产生压缩态的周期性条件;测得压缩态的周期,可得到铁磁材料的一些重要的物理量的信息,如交互积分等.实验表明,利用铁磁共振扩散实验可以检测磁振子的压缩态,压缩程度越大,共振吸收系数(RAC)越小.实验还表明,磁振子压缩态的量子涨落小于相干态时的量子涨落,这也提高了对可观测量的测量精度.

耗散腔中两二能级原子态的自旋压缩量子Fisher信息和最大自旋涨落

在能量耗散腔中,原子用泡利算符描述,光场用相干态描述,运用密度矩阵理论,得到了两二能级原子密度矩阵元的演化规律,分析了与单模辐射场作用过程中原子态的自旋压缩、量子Fisher信息和最大自旋涨落.结果表明:自旋压缩,大于1/2的最大自旋涨落可以作为量子纠缠的充分必要判据.自旋压缩,大于1/2的最大自旋涨落和量子纠缠,它们互相等价.大于1的Fisher信息与它们之间没有等价关系,但可以作为自旋压缩和量子纠缠的充分判据.

μSR技术与穆斯堡尔谱学

本文对近年来发展起来的μSR技术(μ子自旋转动)进行了介绍,并与穆斯堡尔谱学进行了比较,最后讨论了μSR技术在磁学中关于内磁场的测量和自旋动力学方面的研究应用。

中子三轴谱仪的应用

中子三轴谱仪是最早被发明,同时也是应用最广泛的中子散射谱仪之一。它利用了单色器、样品、和分析器3个转动轴的原理,使测量时可以直观地观测倒空间和能量空间的某一个点的散射性质,因此非常适合研究固体中的各种元激发。简单介绍了三轴谱仪的基本原理,然后给出一些三轴谱仪应用的例子。在这些例子中,既包括弹性散射也包括非弹性散射,例如铜单晶中的声子谱,非常规超导体中的磁共振峰,PrO s4As12中的晶格场,以及单层锰氧化合物Pr1-xCa1+xMnO4中的漫散射。

一种面向色纺过程质量异常波动的因素提取方法

为探究色纺纺纱过程中质量特征值的波动机理,对色纺纱质量特征值波动原因进行分析。同时,对影响质量波动不确定因素的产生机理及不确定因素对色纺纱质量的影响行为进行研究。利用灰关联分析方法,设计了影响因素与纺纱质量之间的关联系数和关联度函数,进而提出一种色纺纱关键因素提取方法。结合实验和仿真,最终结果表明:关键因素提取方法能够精准得出不确定因素与色纺纱质量特征值之间的关联系数和关联度,并确定其中的关键因素;进而得出:色纺纱质量波动预测模型有利于实现色纺纱质量特征值波动规律的分析和各类不确定因素对色纺纱质量特征值影响的预警,从而为我国纺织行业提供智能分析色纺纱质量问题和提高资源利用率的理论依据。

低渗杂LaSrCuO C-轴光导(英文)

本文提出自旋涨落协助跃迁光导理论 ,理论计算与实验一致 ,因此本文认为低掺杂铜氧化物的C -轴光导的异常行为可以用自旋涨落协助跃迁光导理论解释。

强关联体系中的自旋与电荷密度涨落的共存性(英文)

对于具有晶格结构的固体 ,利用在相对论狄喇克方程的非相对论极限下得到的电子自旋—轨道相互作用 推导出自旋涨落—声子相互作用。利用此相互作用推导出自旋磁化率、电荷极化率、声子格林函数的一组自洽方程 然后 。