Scientific Review: New Software for Neutron Scattering Data Visualization

New software for neutron scattering data visualization, reduction, and analysis is being developed at IPNS through collaboration between IPNS and the University of Wisconsin-Stout. Recent advances in this Integrated Spectral Analysis Workbench (ISAW) package include: 1) a data analysis package for Single Crystal Diffractometers, 2) a data reduction package for small angle scattering, 3) wizards-a new method of operation which allows the user to step through a series of input forms to do a complete analysis, and 4) a newly designed set of viewers which work with basic data arrays and thus do not require the more complex data objects used for the first generation of viewers.     

凝聚体中的拓扑量子态

探寻拓扑上非平庸的凝聚体物质状态,特别是其电子结构和输运性质,是当前凝聚体物理 学领域非常重要的前沿研究方向。本文讨论的大多数主题都与电子波函数的拓扑性质有关。全文 除简短的引言外,包括拓扑量子现象、各种拓扑相、拓扑性准粒子的异常输运性质、拓扑性集 体激发和耦合激发,以及继续发展的拓扑量子态研究五个章节。这些章节着重反映拓扑量子态研 究的各个侧面,汇总起来方可以凸显凝聚体中拓扑量子态的全貌。     

Compton Scattering of Attosecond X-Ray Pulses on a Hydrogen Atom

The Compton scattering of attosecond X-ray pulses on a hydrogen atom has been studied theoretically in terms of the spectral angular scattering probability during the action of a pulse. The dependence of scattering on the carrier frequency, pulse duration, and scattering angle has been analyzed. It has been shown that the probability of the process at certain parameters of the problem is a nonlinear function of the pulse duration.     

Book Review: Classical and Quantum Dynamics in Condensed Phase Simulations

Journal of Statistical Physics -     

中子散射对快中子照相质量影响的分析

通过一内空的圆柱体模型，对在快中子照相时由样品引起的散射中子强度与样品形状和探测距离之间的关系进行模拟，并用^241Am—Be作中子源对散射中子的影响进行实验验证。结果表明，在快中子照相时，由样品引起的散射中子的强度与探测距离以及样品形状有关。对于同一样品，探测距离增加，散射中子的影响则降低。The relationships between intensities of scattered neutrons by specimens and their shapes and detecting distances have been simulated using a hollow cylinder model, and the results were validated by experiments of fast neutron imaging using ^241Am-Be neutron source. The results showed that the intensities of scattered neutrons are closely related to the detecting distances and sample＇ s shapes. The influences of scattered neutronns in fast neutron imaging will be reduced while detecting distances increased.     

Scientific Review: Prospects and Challenges in Single Crystal Diffuse Scattering

Until comparatively recently, condensed matter physics was mostly concerned with understanding the properties of ideally crystalline solids, and this has led to a detailed understanding of both the structure and dynamics of well-ordered materials. There is however growing interest in understanding complex materials in which disorder, and the nanoscale self-organization associated with it, plays an important role in their bulk properties, as many new phenomena that are attracting considerable interest in materials science are enhanced by the controlled introduction of quenched disorder [1]. Examples include magnetoresistive oxides, superconducting cuprates, ferroelectric relaxors, and fast-ion conductors.     

Real Space Triplets in Quantum Condensed Matter: Numerical Experiments Using Path Integrals,Closures, and Hard Spheres

Path integral Monte Carlo and closure computations are utilized to study real space triplet correlations in the quantum hard-sphere system. The conditions cover from the normal fluid phase to the solid phases face-centered cubic (FCC) and cI16 (de Broglie wavelengths 0.2≤λB*<2, densities 0.1≤ρN*≤0.925). The focus is on the equilateral and isosceles features of the path-integral centroid and instantaneous structures. Complementary calculations of the associated pair structures are also carried out to strengthen structural identifications and facilitate closure evaluations. The three closures employed are Kirkwood superposition, Jackson–Feenberg convolution, and their average (AV3). A large quantity of new data are reported, and conclusions are drawn regarding (i) the remarkable performance of AV3 for the centroid and instantaneous correlations, (ii) the correspondences between the fluid and FCC salient features on the coexistence line, and (iii) the most conspicuous differences between FCC and cI16 at the pair and the triplet levels at moderately high densities (ρN*=0.9, 0.925). This research is expected to provide low-temperature insights useful for the future related studies of properties of real systems (e.g., helium, alkali metals, and general colloidal systems).     

Quantum Entanglement Dynamics of Two Atoms in Quantum Light Sources

Quantum entanglement dynamics of two Tavis-Cummings atoms interacting with the quantum light sources in a cavity is investigated. The results show the phenomenon that the concurrence disappears abruptly in a finite time, which depends on the initial atomic states and the properties of squeezed states. We find that there are two decoherence-free states in squeezed vacuum fields: one is the singlet state, and the other entangled state is the state
that combines both excited states and ground states with a relative phase being equal to the phase of the squeezed state.     

Direct observation of tunneling in KDP using Neutron Compton scattering

Neutron Compton scattering measurements presented here of the momentum distribution of hydrogen in KH2PO4 just above and well below the ferroelectric transition temperature are sufficiently sensitive to show clearly that the proton is coherent over both sites in the high temperature phase, a result that invalidates the commonly accepted order-disorder picture of the transition. The Born-Oppenheimer potential for the hydrogen, extracted directly from data for the first time, is consistent with neutron dif-fraction data, and the vibrational spectrum is in substantial agreement with infrared absorption measurements. The measurements are sensitive enough to detect the effect of surrounding ligands on the hydrogen bond, and can be used to study the systematic effect of the variation of these ligands in other hydrogen bonded systems.     

Aspects of Entanglement in Quantum Many-Body Systems

Knowledge of the entanglement properties of the wave functions commonly used to describe quantum many-particle systems can enhance our understanding of their correlation structure and provide new insights into quantum phase transitions that are observed experimentally or predicted theoretically. To illustrate this theme, we first examine the bipartite entanglement contained in the wave functions generated by microscopic many-body theory for the transverse Ising model, a system of Pauli spins on a lattice that exhibits an order-disorder magnetic quantum phase transition under variation of the coupling parameter. Results for the single-site entanglement and measures of two-site bipartite entanglement are obtained for optimal wave functions of Jastrow-Hartree type. Second, we address the nature of bipartite and tripartite entanglement of spins in the ground state of the noninteracting Fermi gas, through analysis of its two- and three-fermion reduced density matrices. The presence of genuine tripartite entanglement is established and characterized by implementation of suitable entanglement witnesses and stabilizer operators. We close with a broader discussion of the relationships between the entanglement properties of strongly interacting systems of identical quantum particles and the dynamical and statistical correlations entering their wave functions.     

Scientific Review: A New Epithermal Neutron Diffractometer at KENS (EXCED)

Neutron scattering experiments on highly absorbing materials like boron (10B), cadmium (113Cd), rare earths (Sm, Eu, Gd, Dy), etc., are extremely difficult to perform and have so far discouraged research activities on relevant compounds. However, recent topical phenomena such as charge ordering and orbital ordering have highlighted the importance of studying 4f-electron systems and raised a large demand for neutron scattering studies. Unfortunately, the preparation of isotope enriched (weakly absorbing) samples are costly, and very often the large amount of sample required for experiments can not be produced. An alternative way consists of reducing the absorption cross-section _a by utilizing epithermal neutrons of the order of several eV.     

Calculation of Nuclear Deeply Virtual Compton Scattering in HERMES Experiment

We investigate the possibility to acquire information of nuclear generalized parton distribution （GPD） H by studying the deeply virtual Compton scattering （DVCS） off several nuclear targets at the HERMES group （Hadron Electron Ring Accelerator Measurement of Spin）. Two different models are used and developed to demonstrate the leading asymmetry amplitude.A^sinФ LU for coherent-enriched and incoherent-enriched parts with both statistical and systematic uncertainties estimated. It is found that a clear enhancement of ratio of nuclear asymmetry A ^AsinФ to free proton asymmetry A^H,sinФ LU in the coherent-enriched region is expected by both models,and a decrease of the ratio in incoherent-enriched region; both give the information about nuclear modifications. It is also possible to distinguish between those two models even under the limited statistics.     

Spatial Entanglement of Fermions in One-Dimensional Quantum Dots

The time-dependent quantum Monte Carlo method for fermions is introduced and applied in the calculation of the entanglement of electrons in one-dimensional quantum dots with several spin-polarized and spin-compensated electron configurations. The rich statistics of wave functions provided by this method allow one to build reduced density matrices for each electron, and to quantify the spatial entanglement using measures such as quantum entropy by treating the electrons as identical or distinguishable particles. Our results indicate that the spatial entanglement in parallel-spin configurations is rather small, and is determined mostly by the spatial quantum nonlocality introduced by the ground state. By contrast, in the spin-compensated case, the outermost opposite-spin electrons interact like bosons, which prevails their entanglement, while the inner-shell electrons remain largely at their Hartree–Fock geometry. Our findings are in close correspondence with the numerically exact results, wherever such comparison is possible.