Experimental Simulation of Spin Squeezing by Nuclear Magnetic Resonance

We report on the experimental simulation of spin squeezing using a liquid-state nuclear magnetic resonance (NMR) quantum information processor. This was done by identifying the energy levels within the symmetric subspace of a system of n spin-1/2 nuclei with the energy levels of the simulated spin-(n/2) system. The results obtained for our simulations of spin-1 and spin-3/2 systems are consistent with earlier theoretical studies of spin squeezing, and illustrate interesting relations between the degree of squeezing and the strength of the correlations among the underlying spin-1/2 particles.     

Controlling Spin Qubits in Quantum Dots

We review progress on the spintronics proposal for quantum computing where the quantum bits (qubits) are implemented with electron spins. We calculate the exchange interaction of coupled quantum dots and present experiments, where the exchange coupling is measured via transport. Then, experiments on single spins on dots are described, where long spin relaxation times, on the order of a millisecond, are observed. We consider spin-orbit interaction as sources of spin decoherence and find theoretically that also long decoherence times are expected. Further, we describe the concept of spin filtering using quantum dots and show data of successful experiments. We also show an implementation of a read out scheme for spin qubits and define how qubits can be measured with high precision. Then, we propose new experiments, where the spin decoherence time and the Rabi oscillations of single electrons can be measured via charge transport through quantum dots. Finally, all these achievements have promising applications both in conventional and quantum information processing. PACS: 03.67.Lx, 03.67.Mn, 73.23.Hk, 85.35.Be     

电子自旋的时间量子控制

提出一种时间量子控制方案,通过控制所加外部控制场的作用时间能有效地控制电子自旋到达给定的目标量子态,同时发现电子自旋状态能随控制场作用时间呈周期性变化．讨论了外部控制场与其作用时间的关系,结果表明：对于给定的量子控制任务。在选定的某个周期内,作用时间与控制场强度成反比．     

Theory of Single Spin Detection with STM

We propose a mechanism for detection of a single spin center on a non-magnetic substrate. In the detection scheme, the STM tunnel current is correlated with the spin orientation. In the presence of magnetic field, the spin precesses and the tunnel current is modulated at the Larmor frequency. The mechanism relies on the effective spin-orbit interaction between the injected unpolarized STM current and the local spin center, which leads to the nodal structure of the spatial signal profile. Based on the proposed mechanism, the strongest spin-related signal can be expected for the systems with large spin-orbit coupling and low carrier concentration. PACS: 74.40.Gk; 72.70.+m; 73.63.Kv; 85.65.+h     

Feedback Control of Spin Systems

The feedback stabilization problem for ensembles of coupled spin 1/2 systems is discussed from a control theoretic perspective. The noninvasive nature of the bulk measurement allows in principle for a fully unitary and deterministic closed loop. The Lyapunov-based feedback design presented does not require spins that are selectively addressable. With this method, it is possible to obtain control inputs also for difficult tasks, like suppressing undesired couplings in identical spin systems.      

基于小波变换的无驱动结构微机械陀螺信号自旋频率的提取

针对一种新型陀螺,它能敏感旋转载体的俯仰、偏航和滚转角速度,敏感信号是一种调幅波信号,载波频率是自旋频率,包络是横向角速度。实际应用中,需要精确提取自旋频率。基于此,提出了一种提取载波频率的新的方法——小波变换构造解析函数法,对自旋频率解算算法进行了理论推导,并通过MATLAB软件对噪声比为30 dB的模拟陀螺调幅波信号进行了自旋频率的提取和误差分析,其中Hilbert变换相对误差为0.033 6,小波变换相对误差为0.017 8。对三轴精密转台实时测试的横向角速度为180°/s的陀螺信号进行了自旋频率的提取和误差分析,其中Hilbert变换相对误差为0.035 9,均方差MSE为7.915 9;小波变换相对误差为0.001 8,均方差MSE为0.293 7。小波变换较Hilbert变换求解自旋频率精度提高二十倍,降噪性能和频率稳定性更好。     

Atomic Spin Polarization Controllability Analysis: A Novel Controllability Determination Method for Spin-Exchange Relaxation-Free Co-Magnetometers

This paper investigates the atomic spin polarization controllability of spin-exchange relaxation-free co-magnetometers(SERFCMs). This is the first work in the field of controllability analysis for the atomic spin ensembles systems, whose dynamic behaviors of spin polarization are described by the Bloch equations. Based on the Bloch equations, a state-space model of the atomic spin polarization for SERFCM is first established,which belongs to a particular class of nonlinear systems. For this clas...     

离心解脱试验中瞬时转速的测试程序

如何动态地对离心电机的转速进行测试,为产品离心解脱试验中解脱时的解脱加速度的计算提供准确的转速值,从而保证产品的质量,这是个非常的重要问题。针对这个问题,编制了一套基于LabVIEW的离心解脱试验中瞬时转速的测试程序,对产品离心解脱试验中产品解脱时的速度进行实时测试,为产品离心解脱试验及类似的转速测试提供了强有力的技术支持。     

基于MEMS传感器的风洞尾旋姿态测量研究

尾旋是飞机在失去控制后的一种极危险的飞行状态,陷入尾旋极易造成飞机的坠毁,在飞机研制过程中为了提高其机动性及抗尾旋能力,必须对这种极限飞行状态进行研究。在立式风洞中开展尾旋试验是目前效率最高,安全性最有保障的技术手段。试验测试的主要参数是飞机在尾旋及改出过程中的姿态角（包括俯仰角、偏航角和滚转角）。在此简要介绍了通过陀螺仪、加速度计和地磁计进行姿态数据融合的算法,以及采用了一种MEMS传感器进行尾旋姿态测量的试验技术,并且其姿态数据可由Zigbee无线数据模块实时传送到测量计算机。通过试验验证,该技术简单有效,不受现场环境限制,系统动态性能稳定可靠,角度测试精度为优于1°,满足了试验需求,提高了试验效率及数据质量。     

Spin stiffness of vector spin glasses

We study domain-wall excitations for O(m) vector spin glasses in the limit m→∞, where the energy landscape is simplified considerably compared to XY or Heisenberg models due to the complete disappearance of metastability. Using numerical ground-state calculations and appropriate pairs of complementary boundary conditions, domain-wall defects are inserted into the systems and their excitation energies are measured. This allows us to determine the stiffness exponents for lattices of a range of spatial dimensions d=2,…,7. Compiling these results, we can finally determine the lower critical dimension of the model. The outcome is compared to estimates resulting from field-theoretic calculations.     

Spin light of the electron in dense matter

We derive the modified Dirac equation for an electron subject to Standard-Model interaction with nuclear matter. Exact solutions to this equation and the electron energy spectrum in matter are obtained. This establishes rather a powerful method of studying different processes which are possible when electrons propagate in background matter. On this basis, we study in detail the spin light of the electron (SLE) in nuclear matter, a new type of electromagnetic radiation which can be emitted by electronsmoving in dense matter. It is expected that this introduced mechanism of electromagnetic radiation can have applications in astrophysics and cosmology (in particular, the SLE can be turned on when a relativistic electron penetrates into the dense matter of a neutron star). The developed theory of new mechanism of electromagnetic radiation by an electron in nuclear matter can be applied in a straightforward manner to the case of an electron propagating through a dense neutrino gas. The SLE in neutrino environment may take place during supernova explosions and gamma-ray bursts.     

Controllability of One Spin and Two Interacting Spins

Mathematics of Control, Signals, and Systems - ?We consider the problem of steering control for the systems of one spin ½ particle and two interacting spin ½ particles in an...     

Input-Output Equivalence of Spin Networks under Multiple Measurements

Two quantum control systems that are driven by an external field are said to be input–output equivalent if, for any control field, the measured value of a given observable is the same. Equivalent models cannot be distinguished by experiments involving state evolutions and measurements. In this paper, we characterize the equivalent models of networks of spin driven by electro-magnetic fields for which the expectation value of the total magnetization is measured. Extending previous results and definitions that only dealt with the case of a single measurement, we describe the class of equivalent models under a sequence of Von Neumann measurements. The results are motivated by the problem of parameter identification for Heisenberg spin systems modeling molecular magnets.Mathematics Subject Classifications (2000): 93B30, 17B45, 17B81Partially supported by M.I.U.R., project Viscosity, metric, and control theoretic methods for nonlinear partial differential equations.Supported by NSF Career Grant, ECS0237925.     

基于光惯组合的风洞尾旋试验位姿参数测量方法

尾旋是飞机在失速时的一种复杂而危险的非正常飞行状态。研究飞机尾旋及改出特性的常用方法是开展立式风洞尾旋试验,其中测量方法是试验中的关键技术。在十几年的发展历程中,先后经历了双目立体视觉、编码标记图像识别和惯性航姿测量的技术改进,在不断提升的过程中对测量能力和数据质量也提出了更高要求,因此发展了一种基于光惯组合技术的尾旋6自由度数据测量方法,通过惯性系统测量三维姿态,光学系统测量空间位置信息。经过试验验证,该方法成功获取了尾旋模型6自由度数据,测量效率高,数据无缺失,根据模型运动轨迹在试验段截面投影可获得尾旋半径,增加了对于尾旋现象的认知维度。     

某型飞机模型失速/尾旋飞行试验技术

根据某型飞机失速／尾旋飞行试验参数测试的需要,提出一种飞机模型自由飞失速／尾旋飞行试验的测试技术,该技术包含测量原理与方法、测试系统组成、具体的实施步骤和方法、数据处理流程以及测量精度的检查等。经过10多架次的飞行试验证明,该技术实用、安全,测量数据可靠、精度高,测量结果能够满足此型号飞机失速／尾旋飞行试验的要求,并可在同类飞行试验课题中推广应用。     

Molecular spin in nano-confined fluidic flows

In this paper, we study the effect of molecular spin on the fluid dynamics of molecular nano-confined fluids using the extended Navier–Stokes equations. We show that the effect of spin is non-negligible for non-steady flows and we then discuss two examples, namely, a zero mean oscillatory flow and an oscillatory lid driven cavity flow. In the discussion of the former, we propose a dimensionless quantity that qualitatively predicts the effect of the spin. From this it is shown that only for sufficiently small system sizes and extremely high frequencies will molecular spin be relevant, depending on the molecular fluid’s rotational inertia and the rotational viscosity. In the lid driven cavity flow we observe that the thermodynamic energy dissipation due to molecular spin undergoes period doubling when increasing the Reynolds number and, under some circumstances, it may be negative.     

制导炮弹转速测量技术研究进展与展望

制导炮弹是由常规火炮发射,在飞行过程中进行搜索、导引和控制,能够对目标实施精确点打击的制导武器.制导炮弹转速的精确测量是实现精确制导和控制的基础.对制导炮弹转速测量技术进行了综述,首先,论述了制导炮弹的发展现状,接着分析了制导炮弹转速测量的必要性,并且阐述了制导炮弹转速测量的特点;然后,对现有旋转弹转速测量的方法和手段加以总结,并指出了适用于制导炮弹的转速测量及信息处理方法,包括利用磁阻传感器和高动态振动陀螺测量制导炮弹转速的原理以及关键技术;最后,指出了制导炮弹转速测量技术今后的研究方向和研究重点.     

Spin coherent states phenomena probed by quantum state tomography in Zeeman perturbed nuclear quadrupole resonance

Recently, we reported an experimental implementation of quantum information processing (QIP) by nuclear quadrupole resonance (NQR). In this work, we present the first quantum state tomography (QST) experimental implementation in the NQR QIP context. Two approaches are proposed, employing coherence selection by temporal and spatial averaging. Conditions for reduction in the number of cycling steps are analyzed, which can be helpful for larger spin systems. The QST method was applied to the study of spin coherent states, where the alignment-to-orientation phenomenon and the evolution of squeezed spin states show the effect of the nonlinear quadrupole interaction intrinsic to the NQR system. The quantum operations were implemented using a single-crystal sample of KClO\(_{3}\) and observing \(^{35}\)Cl nuclei, which posses spin 3/2.     

Spin Squeezing Criterion with Local Unitary Invariance

We propose a spin squeezing criterion for arbitrary multi-qubit states that is invariant under local unitary operations. We find that, for arbitrary pure two-qubit states, spin squeezing is equivalent to entanglement, and multi-qubit states are entangled if this new spin squeezing parameter is less than unity. PACS: 03.67.-a; 03.65.Ud     

Nuclear polarization and entanglement in spin systems

We investigated relationships between entanglement measures and the order parameter (nuclear polarization) in nuclear spin systems controlled by the nuclear magnetic resonance (NMR) technique. Since spin polarization can be easily manipulated by the NMR technique, experimentalists are presented with an opportunity to study the dynamic properties of entanglement, i.e., the creation and evolution of entangled states. Our approach may constitute the basis for researching the relations between the entanglement measures and measurable parameters of order in other quantum systems. An erratum to this article can be found at