Conservation of Angular Momentum in a Flux Qubit

Oscillations of superconducting current between clockwise and counterclockwise directions in a flux qubit do not conserve the angular momentum of the qubit. To compensate for this effect the solid containing the qubit must oscillate in unison with the current. This requires entanglement of quantum states of the qubit with quantum states of a macroscopic body. The question then arises whether slow decoherence of quantum oscillations of the current is consistent with fast decoherence of quantum states of a macroscopic solid. This problem is analyzed within an exactly solvable quantum model of a qubit embedded in an absolutely rigid solid and for the elastic model that conserves the total angular momentum. We show that while the quantum state of a flux qubit is, in general, a mixture of a large number of rotational states, slow decoherence is permitted if the system is macroscopically large. Practical implications of entanglement of qubit states with mechanical rotations are discussed.     

Dynamics of a Flux Qubit Coupled with a Quantized Electromagnetic Mode of a Lossy Cavity

The dynamics of a rf-SQUID qubit placed within a 1-D lossy resonant cavity is reported. Initially preparing the combined system in a state with no more than one excitation, the effects of loss mechanisms can be carefully analyzed, for different values of the cavity quality factor Q. The results here discussed demonstrate the possibility of controlling these phenomena in such a way to be able to observe “coherent” Rabi oscillations and the periodically generation of factorized and entangled states (with a priori known characteristics). The importance of these results in the general context of quantum communications is carefully discussed as well as some technical detail necessary for the experimental feasibility of my theoretical scheme.     

Dispersive Charge and Flux Qubit Readout as a Quantum Measurement Process

We analyze the dispersive readout of superconducting charge and flux qubits as a quantum measurement process. The measurement oscillator frequency is considered much lower than the qubit frequency. This regime is interesting because large detuning allows for strong coupling between the measurement oscillator and the signal transmission line, thus allowing for fast readout. Due to the large detuning we may not use the rotating wave approximation in the oscillator-qubit coupling. Instead we start from an approximation where the qubit follows the oscillator adiabatically, and show that non-adiabatic corrections are small. We find analytic expressions for the measurement time, as well as for the back-action, both while measuring and in the off-state. The quantum efficiency is found to be unity within our approximation, both for charge and flux qubit readout.      

Experiments on a Superconducting Qubit Manipulated by Fast Flux Pulses: The Issue of Non-adiabaticity

The double SQUID qubit is a superconducting interferometer (SQUID) made of two Josephson junctions and two superconducting loops. Its energy potential can be greatly modified in shape and symmetry by using two magnetic control fluxes that can change the potential from a double well to an almost harmonic single well: This feature is exploited for manipulating the qubit without resorting to the usual NMR-like techniques with microwave irradiation. The qubit machinery relies on these operations being performed non-adiabatically, realizing a transition between the two lowest-lying energy levels, at the same time avoiding excitation of upper levels, a condition that can be satisfied by using control pulses with proper risetime. We show experimental results referring to manipulation of the qubit at different rates and make a qualitative comparison with theoretical expectations.     

Spin Degree of Freedom and Tunneling through a Quantum Dot

A review is given on theoretical studies of roles of the spindegree of freedom in transport through a quantum dot with thetotal spin S for N electrons and for N+1electrons in the ground state. The conductance and the phasecoherency are expressed in terms of universal functions ofS, , and the spin splitting at small tunnelingrates in the absence of spin-orbit interactions and are shownto exhibit the correlation between tunnelings of electronswith opposite spins and the dephasing due to spin flips.     

单自由度含间隙和干摩擦碰撞振动系统的分岔与混沌

建立了单自由度含间隙和干摩擦的碰撞振动系统的动力学模型,利用半解析、数值摸拟方法求解系统的响应并给出了判定系统粘滑碰撞准则,阐述了判定系统周期运动稳定性的理论方法,对系统在不同摩擦力影响所呈现出的动力学行为进行了非线性动力学分析,并进一步分析了由干摩擦导致的粘-滑振动行为.     

爆炸冲击荷载作用下SRC柱等效单自由度模型

爆炸冲击荷载作用下结构构件的反应分析方法常用的是等效单自由度模型，在现有的有关资料中，等效单自由度模型主要用于钢筋混凝土构件和钢构件。等效单自由度模型的关键是确定等效弹性位移、破坏位移和屈服强度。以通用有限元分析软件LS—DYNA为基础，研究了钢骨混凝土（SRC）柱在爆炸冲击荷载作用下的反应特征，确定出了等效单自由度模型的等效弹性位移和破坏位移；以常规SRC柱设计理论为基础，提出了等效单自由度模型的等效屈服强度计算公式。最后用所建立的等效单自由度模型和LS—DYNA软件分别对8根SRC柱共48种爆炸冲击荷载工况进行对比分析，验证了所提出的等效单自由度模型。     

机械合金化与热处理制备Al3Ti金属间化合物

以高纯Al粉和Ti粉为原料,通过高能球磨机械合金化和空气中热处理制备了Al3Ti金属间化合物粉末.使用XRD和SEM测试分析了球磨过程中粉末的物相结构和形貌的变化过程,对热处理后的粉末进行了XRD晶体结构测试.结果表明,高能球磨60h后,原料粉末转变为非晶态粉末.将非晶态粉未在500℃以上热处理后,转变为Al3 Ti金属间化合物.     

滞后阻尼结构的复模态综合技术及其界面自由度的减缩

本文在Craig固定界面模态综合法基础上提出了一个针对滞后阻尼结构的复模态综合方法。算例说明该方法不仅在频率上,而且在振型上都具有较好的精度。本文还探讨了综合自由度的进一步减缩。     

氮气流量对UBMS制备TiN薄膜结构和力学性能的影响

利用非平衡磁控溅射离子镀技术研究了不同氮气流量对TiN薄膜结构、摩擦性能、附着力及显微硬度的影响.研究结果表明:N2流量对TiN薄膜的择优取向有很大影响,N2流量较小时,TiN薄膜显示出{111}择优取向生长趋势,在N2流量为15sccm条件下沉积的TiN薄膜的(111)衍射峰强度最强,与之对应的薄膜硬度和膜基结合强度最高,耐磨性能也最好;N2流量的大小对TiN薄膜的沉积速率和摩擦系数影响显著,并随N2流量增加都有较明显的下降趋势.     

碳纳米管和氧化铝混杂增强铝基复合材料的制备及力学性能

采用化学气相沉积结合机械球磨的方法制备了碳纳米管(CNTs)和Al_2O_3颗粒混杂增强铝基复合材料,研究了球磨时间、Al_2O_3含量对复合材料组织和力学性能的影响。结果表明:本方法可以获得CNTs和Al_2O_3颗粒在铝基体内的均匀分散。随球磨时间的增加,复合材料的硬度随之增大;当球磨时间为180min时,复合材料硬度达纯铝的2.1倍。此外,随Al_2O_3颗粒含量的增加,复合材料的硬度和压缩屈服强度均不断提高。当Al_2O_3的质量分数为4%时,CNTsAl_2O_3/Al复合材料的硬度达112.1HV,为纯铝的2.8倍;压缩屈服强度达416MPa,为纯铝的4.6倍,说明CNTs和Al_2O_3的混杂加入发挥了良好的协同增强效果。     

The Effect of Magnetic Field on a Quantum Rod Qubit

The Hamiltonian of a quantum rod (QR) with an ellipsoidal boundary is given after a coordinate transformation, which changes the ellipsoidal boundary into a spherical one. We then study the eigenenergies and eigenfunctions of the ground and the first excited states of an electron strongly coupled to the LO-phonon in the QR under a magnetic field. The present system may be used as a two-level qubit. When the electron is in the superposition state of the ground and the first excited states, we obtained the time evolution of the electron probability density oscillating in the QR. It is found that the magnitude of the probability density is increased by the magnetic field, whereas it decreases the oscillation period of the probability density. The oscillation period is a increasing function of the ellipsoid aspect ratio, the transverse and longitudinal effective confinement lengths of the QR, but a decreasing one of the electron-phonon coupling strength and the cyclotron frequency of the magnetic field.     

二自由度线性系统跌落响应影响因素分析

把运输包装件简化为两自由度系统,基于Matlab,运用四阶龙格-库塔法对具有线性弹性材料的缓冲包装系统进行数值分析,分别讨论了跌落高度、阻尼比、频率比、质量比对主体及易损件位移及加速度响应的影响;该方法和结论对缓冲包装设计具有重要意义.     

机器人手指尖六维力/力矩传感器的研制

提出一种机器人手指尖六维力／力矩传感器,并对其弹性体结构进行详细论述;分析应变量与测量量的对应关系;采用现代设计手段对弹性体进行模态分析,并介绍了传感器放大处理电路,给出实验结果。     

线性冲击隔离系统的抗冲击性能及参数优化研究

对单自由度线性冲击隔离系统的最优抗冲击性能进行了理论研究,推导了抗冲击性能指标J1和J2之间的关系,获得了最优参数的表达式,为线性冲击隔离系统的设计提供了理论基础。     

人体6自由度运动参数无线测试系统BTViewer的设计与开发

为解决测试人体在三维空间中的关节运动参数,自主设计了人体六自由度运动参数测试系统BTViewer.基于惯性传感器跟踪技术,设计了整体的系统平台工作流程,同时完成了相关算法.为降低误差、减少漂移现象,本实验采用集成的三轴加速度计、三轴磁力计的模块LSM303DLH以及三轴陀螺仪动态采集样本数据,通过无线装置传输到电脑,有效合理地对采集到的数据进行预处理,将原始数据互补滤波之后解析成实际数据,准确地得到人体六自由度运动参数.最后,运用Qt集成的OpenGL等模块进行曲线、三维等可视化显示.实验表明,该系统的设计达到了预期的要求,能够较好地跟踪人体6自由度运动参数.     

Magnetic Flux Penetration in a Mesoscopic Superconductor with a Slit

In this work, the vortex nucleation process in a mesoscopic squared superconductor with a slit is numerically investigated in terms of time dependent Ginzburg–Landau theory. We have calculated, simultaneously, the Gibbs free energy and the vortex configuration in function of time, it allows to identify the correspondence between special points in the Gibbs free energy and the configuration of the vortex system.     

Dynamics of Uniaxial Tension of a Viscoelastic Strain-Hardening Body in a System with One Degree of Freedom. Part 4. Action of an External Force on a Compound Body

A rheological model and the dynamics of an open mechanical system, comprising an elastic machine element and a compound body consisting of two irreversibly deformable bodies connected in series with one degree of freedom under the action of an external force are considered. If the system is subjected to a load below the elastic limit of both bodies, the motion of the mechanical system is described by a classical second-order dynamic system. If the system is subjected to a load above the elastic limit of one of the bodies, the motion of the mechanical system is described by a third-order dynamic system, and when it is loaded above the elastic limit of both bodies, the motion is described by a dynamic system of two third-order differential equations. The solutions of this dynamic system are damped oscillations in character, with the damping factor increasing with the ratios of the elastic stiffness and strain hardening values to the value of viscous resistance of deformable bodies.     

MWCNTs/PVC电纺纤维及其力学性能

用静电纺技术制备了多壁碳纳米管/聚氯乙烯(MWCNTs/PVC)超细纤维,对复合纤维的形貌、结构、结晶行为及热稳定性进行了分析测试,着重研究了复合纤维膜的力学性能与MWCNTs用量的关系。结果表明,MWCNTs能有效地分散于PVC溶液中,并成功纺出MWCNTs/PVC超细纤维。随着MWCNTs含量的增加,纤维直径变细,改善了纤维的结晶性,但热稳定性变差。纤维膜的拉伸断裂强度和断裂伸长率随MWCNTs含量增加出现先增加后下降的趋势。     

Ti对金红石型药芯焊丝熔敷金属组织性能影响

以金红石型药芯焊丝为基础,通过在焊丝中加入不同含量的钛铁,研究了Ti对熔敷金属组织及力学性能的影响。结果表明,随焊丝钛含量的增加,脱氧方式从Ti、Si、Mn联合脱氧逐渐转为以Ti脱氧为主,且熔敷金属中夹杂物的Ti含量逐渐增大,同时熔敷金属中合金元素含量增加,屈服强度逐渐趋近抗拉强度,塑性变差。组织分析发现,以复合氧化物形式存在的化合钛对针状铁素体的形成有促进作用,以合金元素形式存在的固溶钛对针状铁素体的形成有抑制作用。