Teleportation and thermal entanglement in two-qubit Heisenberg X Y Z spin chain with the Dzyaloshinski-Moriya interaction and the inhomogeneous magnetic field

This paper studies the average fidelity of teleportation and thermal entanglement for a two-qubit Heisenberg X Y Z chain in the presence of both an inhomogeneous magnetic field and a Dzyaloshinski-Moriya interaction. It shows that for a fixed Dz, the increase of bz will broaden the critical temperature at the cost of decreasing the thermal entanglement. And it can modulate the inhomogeneous magnetic field and the Dzyaloshinski-Moriya interaction for the average fidelity of teleportation to be optimal.     

The quantum compass chain in a transverse magnetic field

We study the magnetic behaviors of a spin-1/2 quantum compass chain (QCC) in a transverse magnetic field, by means of the analytical spinless fermion approach and numerical Lanczos method. In the absence of the magnetic field, the phase diagram is divided into four gapped regions. To determine what happens by applying a transverse magnetic field, using the spinless fermion approach, critical fields are obtained as a function of exchanges. Our analytical results show, the field-induced effects depend on in which one of the four regions the system is. In two regions of the phase diagram, the Ising-type phase transition happens in a finite field. In another region, we have identified two quantum phase transitions (QPT)s in the ground state magnetic phase diagram. These quantum phase transitions belong to the universality class of the commensurate-incommensurate phase transition. We also present a detailed numerical analysis of the low energy spectrum and the ground state magnetic phase diagram. In particular, we show that the intermediate state (h _c1 < h < h _c2) is gapful, describing the spin-flop phase.     

Bipartite entanglement of a two-qubit system with anisotropic couplings under nonuniform magnetic fields

This paper investigates bipartite entanglement of a two-qubit system with anisotropic couplings under an inhomogeneous magnetic field. This work is mainly to investigate the characteristics of a Heisenberg XYZ chain and obtains some meaningful results. By the concept of negativity, it finds that the inhomogeneity of magnetic field may induce entanglement and the critical magnetic field is independent of J_z. The inhomogeneous magnetic field can increase the value of critical magnetic field B_c. It also finds that the magnetic field not only suppresses the entanglement but also can induce it to revival for some time.     

Huygens' principle in inhomogeneous,isotropic media and a general integral equation applicable to optical resonators

Huygens' principle is derived for short wavelengths in inhomogeneous, isotropic media from considerations of Green's second theorem and the solution to the time-independent wave-equation for a point-source in an inhomogeneous, isotropic medium. This principle leads to an integral equation for the field distribution on optical resonator mirrors, whose parameters depend only upon the geometrical-optics ABCD-matrices. The resonator parametersF, G ₁,G ₂, the resonance and stability conditions as well as the spot size of the fundamental mode at the mirrors are given as functions of A, B, C, D, for the special case of a rotationally symmetric optical system between square mirrors. The resonator parameters,F, G ₁,G ₂, are calculated by this new method for a case familiar from the literature.This work forms part of a dissertation approved by the Faculty of Electrical Engineering of the University (T.H.) of Karlsruhe.     

SÕ(n) — Symmetric field equations

Field equations satisfied by the irreducible realizations of any inhomogeneous pseudo-orthogonal group are derived. For those representations which are characterized by the vanishing of the invariants of the inhomogeneous group, the field equations are of first order, of the formS _{AB p B} =p _A . The possibility of consideringSO(q ₁,q ₂) as a higher symmetry group is discussed briefly.     

EPR and NMR line shapes in disordered ferroelectric crystals

A theory is developed for the magnetic resonance line shape in disordered ferroelectric crystals. In a study of the random fields responsible for inhomogeneous line broadening, nonlinear and spatial correlation effects are taken into account. It is shown that homogeneous broadening depends on the temperature and on the magnitude and orientation of the external magnetic field, as well as on the nonlinearity parameters of the ferroelectric material. The resonance line shape is calculated as the envelope of homogeneously broadened Lorentzian spin packets. Analytic expressions for I ₂(ω) and I ₃(ω) are introduced to account for nonlinearity and correlation effects of second and third order, respectively. Calculations are done for centrally symmetric crystals, as well as for those without a center of symmetry. It is shown that homogeneous broadening is important near the line peak, while the wings are determined mainly by inhomogeneous broadening. Manifestations of the predicted effects in the spectrum lines of disordered ferroelectric crystals are discussed. Fiz. Tverd. Tela (St. Petersburg) 40, 340–347 (February 1998)     

NMRON studies of the antiferromagnetic and paramagnetic phases of54Mn-MnCl2 · 4H2O

Pulsed NMRON, CW NMRON and thermal NMR-NO methods have been utilized to study⁵⁴Mn-MnCl₂ · 4H₂O. The⁵⁴Mn spin-lattice relaxation timeT ₁ in zero applied field has been measured between 35 and 90 mK in the antiferromagnetic phase. Above 65 mK the dominant relaxation mechanism is a Raman process with the electronic magnons, but at lower temperatures a direct process takes over. NMRON has been observed for the first time in the paramagnetic phase, and a line width of 300 kHz, with both homogeneous and inhomogeneous contributions, is observed. In the antiferromagnetic phase the line width is 35 kHz, and there are also homogeneous and inhomogeneous contributions. The dependence ofT ₁ for the⁵⁴Mn spins on field and temperature was studied in the paramagnetic phase. AT ₁ minimum centred atB ₀=2.64 T was observed. The hyperfine parameter <⁵⁴ AS>/h=−513.6(3) MHz in the paramagnetic phase, and comparison with the value in the antiferromagnetic phase gives 0.013(1) for the zero point spin deviation.     

Asymptotic solutions to the Knizhnik-Zamolodchikov equation and crystal base

The Knizhnik-Zamolodchikov equation associated withsl ₂ is considered. The transition functions between asymptotic solutions to the Knizhnik-Zamolodchikov equation are described. A connection between asymptotic solutions and the crystal base in the tensor product of modules over the quantum groupU _q sl ₂ is established, in particular, a correspondence between the Bethe vectors of the Gaudin model of an inhomogeneous magnetic chain and the Q-basis of the crystal base.Dedicated to the memory of Ansgar SchnizerThe author was supported by NSF Grant DMS-9203929     

Polariton reflectance spectra from thin ZnSxSe1−x layers

A study of reflectance spectra from thin ZnS_xSe_1−x solid-solution layers in the region of excitonic resonances is reported. It has been found that an increase in sulfur concentration in the layers increases the inhomogeneous broadening of the quantized polariton lines. It has been established that the inhomogeneous line broadening in a reflectance spectrum depends on the magnitude of exciton-photon mixing; it is small in the long-wavelength region where the photon component of the polariton is large, and large at short wavelengths where the mechanical component dominates. Fiz. Tverd. Tela (St. Petersburg) 40, 867–868 (May 1998)     

Note on the E × B Instability

Without appeal to trial functions an instability criterium for the inhomogeneous plasma slab is derived. The growth rate for the flute type instabilities is expressed in terms of the density perturbation n₁. When n₁ is put equal to the trial function used by SIMON (1963), a growth rate which differs somewhat from that of Simon is found. The reason for the discrepancy is pointed out.     

Statistical modeling of excitation transfer processes in the case of an inhomogeneous dopant distribution

A computer program based on the Monte Carlo method was used to simulate upconversion processes and the migration of excitation in an ensemble of optical centers. The dependence of the upconversion coefficient C _up on the pump power and the concentration of centers are determined for inhomogeneous materials with clusters. It is shown that the nonmonotonic character of the upconversion coefficient dependence on the pump power in inhomogeneous materials is caused by a spatial inhomogeneities of excited centers distribution.     

Single-Pulse Echo and Its Secondary Signals in Two-Level Spin Systems

The dependences of the amplitudes of single- and two-pulse spin echoes and their secondary signals in NMR (protons of glycerin in an inhomogeneous magnetic field) in the exciting-pulse repetition period T _r have been compared. The difference in origin of the primary and secondary signals of a single-pulse echo in a two-level spin system has been confirmed. It is shown that only a primary single-pulse echo observed when T _r > T ₁ (T ₁ is the spin lattice relaxation time) results from single-pulse excitation. The secondary single-pulse echo signals are observed for T _r < T ₁ and are due to the multiphase formation mechanism. The results obtained for magnetically ordered substances are analyzed. Based on these data, it was inferred earlier that primary and secondary single-pulse echo signals were formed by one and the same multiphase mechanism.     

Letter: Spherically Symmetric Metrics with Shear Controlling Expansion

An isotropic spatially inhomogeneous spacetime with the stress tensor satisfying the limiting case of the strong energy condition [T₀₀ + 1/2)T] = 0 in the locally inertial coordinates where the observer's four-velocity is u ^a = ₀ ^a satisfying the constraint u ^a u_a = –1 is studied. Special metrics with accelerating expansions of the inhomogeneous spacetime merely controlled by the shear are presented as an alternative model.     

Theoretical exploration of asymmetric molecular harmonic emission and attosecond pulse generation in the presence of spatially inhomogeneous plasmon-enhanced field

Asymmetric molecular harmonic generation from HeH²⁺ ion in the presence of the spatially inhomogeneous plasmon-enhanced field has been theoretically investigated by solving the two-dimensional non-Born–Oppenheimer time-dependent Schrödinger equation (both the electron and nuclear motions are considered only along the laser polarisation axis). It shows that (1) for the normal homogeneous field, the harmonic cut-off from the asymmetric molecule is beyond the classical harmonic cut-off energy from the atom (I_p + 3.17 U_p). Further analyses show that the multi-channels ionisation–recombination process is responsible for the harmonic extension. (2) For the spatially inhomogeneous plasmon-enhanced field, the harmonic cut-off can be further enhanced, and an optimal 3.0 dB enhanced field with a 482 eV supercontinuum has been obtained. Quantum time-frequency harmonic analyses have been shown to explain the harmonic characteristics and the harmonic extension process. (3) Initial vibrational state and isotopic effects show that intense harmonics can be generated from higher initial vibrational state and the heavier molecule. Finally, by properly superposing the harmonics, a series of sub-30 as attosecond pulses can be obtained.     

Magnetic- and stress-fields of cylindrical non-uniform current density superconducting coils

Superconducting coils with an inhomogeneous current density distribution yield more field for less volume of superconductor. The advantages of these systems are lower costs and an improved cooling. The latter is important for high field magnets. Mechanical stresses induced by the electromagnetic forces are the limiting factor in designing such coils. The inhomogeneous current field is produced by a set of concentric subcoils. The radial and tensile stresses and the radial displacements in the subcoils are calculated. This calculation requires the field-shape in the coils. An exact calculation shows a linear decrease of the field with the radius in each subcoil. Thus the stress-calculations are very simple and one does not need a computer. As an example this method is applied to a 10 T-magnet with three subcoils. In this case the results of our exact calculation differ from the approximation of Kilbet al., Steklyet al. and from the magnetic pressure estimateB ²/2μ ₀ up to a factor of three.     

Methods for correlating T1ρ and FID components in wideline H NMR studies of motionally heterogeneous polymer systems

We address the problem of correlating the observed FID and T_1ρ components in wideline ¹H relaxation measurements of motionally heterogeneous polymers, and show that different methods of data treatment can highlight different aspects of the correlations present. For a sample of polypropylene we find that the T_1ρ relaxation behaviour is driven by relaxation associated with the intermediate FID component, which strongly suggests a motionally inhomogeneous amorphous region in the sample.     

Distributions of transverse relaxation times for soft-solids measured in strongly inhomogeneous magnetic fields

The single-sided NMR-MOUSE sensor that operates in highly inhomogeneous magnetic fields is used to record a CPMG ¹H transverse relaxation decay by CPMG echo trains for a series of cross-linked natural rubber samples. Effective transverse relaxation rates 1/T_2,short and 1/T_2,long were determined by a bi-exponential fit. A linear dependence of transverse relaxation rates on cross-link density is observed for medium to large values of cross-link density. As an alternative to multi-exponential fits the possibility to analyze the dynamics of soft polymer network in terms of multi-exponential decays via the inverse Laplace transformation was studied. The transient regime and the effect of the T₁/T₂ ratio in inhomogeneous static and radiofrequency magnetic fields on the CPMG decays were studied numerically using a dedicated C++ program to simulate the temporal and spatial dependence of the CPMG response. A correction factor T₂/T_2,eff is derived as a function of the T₁/T₂ ratio from numerical simulations and compared with earlier results from two different well logging devices. High-resolution T₁–T₂ correlations maps are obtained by two-dimensional Laplace inversion of CPMG detected saturation recovery curves. The T₁–T₂ experimental correlations maps were corrected for the T₁/T₂ effect using the derived T₂/T_2,eff correction factor.     

外磁场下XY模型中两量子位热纠缠的性质及其调控研究

在海森堡XY模型中,为了统一研究均匀磁场和非均匀磁场对系统热纠缠的影响,在两个量子位分别施加独立可控的外磁场(B+b)和(B-b). 发现在均匀磁场和低温条件下的纠缠度有一个稳定的平台区并发生纠缠突变. 控制磁场不均匀度b和选择合适的材料就可以获得最有利的纠缠,并大大提高系统退纠缠的临界温度T_c. 调节磁场的B值,可以在更宽的温度范围内实现此体系的纠缠开关. 关键词： 热纠缠度 密度矩阵 XY模型')" href="#">XY模型     

One color,pulsed excited-state upconversion in YAG:Tm3+

One color red laser pumping of YAG:Tm³⁺ crystals results in a strong upconverted near ultraviolet and blue fluorescence from the excited¹ D ₂ and¹ G ₄ multiplets. It is found that under pulsed-pumping conditions the quasi-resonant excited-state absorption from the³ H ₄ multiplet is the responsible process. Analysis of the upconverted emission confirmed previous results on³ H ₄ level assignments as well as on inhomogeneous line broadening in the YAG structure.     

Thermal entanglement in two-qutrit spin-1 anisotropic Heisenberg model with inhomogeneous magnetic field

The thermal entanglement of a two-qutrit spin-1 anisotropic Heisenberg XXZ chain in an inhomogeneous magnetic field is studied in detail. The effects of the external magnetic field (B), a parameter b which controls the inhomogeneity of B, and the bilinear interaction parameters J_{x=Jy≠Jz on the thermal variation of the negativity are studied in detail. It is found that negativity N decreases when the values of magnetic field, inhomogeneity b and temperature are increasing. In addition, N remains at higher temperatures for higher values of Jz and lower values of B and b.}