Quantum Entanglement in a System of Two Spatially Separated Atoms Coupled to the Thermal Reservoir

We study quantum entanglement between two spatially separated atoms coupled to the thermal reservoir. The influences of the initial state of the system, the atomic frequency difference and the mean number of the thermal field on the entanglement are examined. The results show that the maximum of the entanglement obtained with nonidentical atoms is greater than that obtained with identical atoms. The degree of entanglement is progressively decreased with the increase of the thermal noise. Interestingly, the two atoms can be easily entangled even when the two atoms are initially prepared in the most mixed states.     

Fabrication of Long-Period Fibre Gratings Using 800 nm Femtosecond Laser Pulses

Long-period fibre gratings inside standard single-mode optical communication fibres are successfully fabricated with infrared femtosecond laser pulses. The refractive index perturbations are well confined within the fibre core by choosing the proper laser focusing parameters and translation speed of the fibre during the direct laser writing process. With the self-focusing effect considered and at a constant average irradiation dose of 1.62 × 10^3 J/（cm^2μm）, the threshold intensity for fabricating long-period gratings with infrared femtosecond laser pulses is determined to be 5.13 × 10^13 W/cm2.     

Suppression of Chaos and Phase Locking in Two Coupled Nonidentical Neurons under Periodic Input

Dynamical behaviour of two coupled neurons with at least one of them being chaotic is presented. Bifurcation diagrams and Lyapunov exponents are calculated to diagnose the dynamical behaviour of the coupled neurons with the increasing coupling strength. It is found that when the coupling strength increases, a chaotic neuron can be controlled by the coupling between neurons. At the same time, phase locking is studied by the maxima of the differences of instantaneous phases and average frequencies between two coupled neurons, and the inherent connection of phase locking and the suppression of chaos is formulated. It is observed that the onset of phase locking is closely related to the suppression of chaos. Finally, a way for suppression of chaos in two coupled nonidentical neurons under periodic input is suggested.     

High Pressure effects on electrical resistivity and dielectric properties of nanocrystalline SnO2

Nanocrystalline tin oxide (SnO₂) was prepared by chemical precipitation method with different grain sizes. The X-ray diffraction studies showed the structural stability of nanocrystalline SnO₂ under high-pressure. Electrical and dielectric properties were studied on these samples using complex impedance spectroscopy under different hydrostatic pressures. Electrical resistivity and dielectric studies showed a transition in nanocrystalline SnO₂ when it was subjected to high-pressure. The transition pressures obtained from both the resistivity and dielectric measurements agree with each other. The transition pressures were found to increase considerably with the decrease in grain size. Dielectric constant was found to decrease with the reduction of grain size. In order to find whether the transition with pressure is structure- related or not, Raman spectroscopy was done at normal temperature and pressure (NTP) and as a function of pressure at room temperature. Raman modes at NTP showed lines which correspond to tetragonal rutile structure of SnO₂. In situ high-pressure Raman measurements were carried out up to 3.38 GPa. No structural change was found with pressure.     

Quantum Secret Sharing with Two-Particle Entangled States

We present a new protocol for the quantum secret sharing （QSS） task among multiparties with two-particle entangled states. In our scheme, the secret is split among a number of participatlng partners and the reconstruction requires collaboration of all the authorized partners. Instead of multiparticle Greenberger-Horne-Zeillnger states, only two-particle entangled states are employed in this scheme. By local operations and individual measurements on either of the two entangled particles, each authorized partner obtains a sequence of secret bits shared with other authorized partners. This protocol can be experimentally realized using only linear optical elements and simple entanglement source. It is scalable in practice.     

Nitrogen-Doped Chemical Vapour Deposited Diamond： a New Material for Room-Temperature Solid State Maser

Electron spin resonance （ESR） in polycrystalline diamond films grown by dc arc-jet and microwave plasma chemical vapour deposition is studied. The films with nitrogen impurity concentration up to 8 × 10^18 cm^-3 are also characterized by Raman, cathodoluminescence and optical absorption spectra. The ESR signal from P1 centre with g-factor of 2.0024 （nitrogen impurity atom occupying C site in diamond lattice） is found to exhibit an inversion with increasing the microwave power in an H102 resonator. The spin inversion effect could be of interest for further consideration of N-doped diamonds as a medium for masers operated at room temperature.     

Controllability of pure states for the Pöschl-Teller potential with a dynamical group SU(2)

The controllability of a quantum system for the modified Pöschl-Teller (MPT) potential with the discrete bound states is investigated. The creation and annihilation operators of this potential are constructed directly from the normalized wave function with the factorization method and associated to an su(2) algebra. It is shown that this quantum system with the nondegenerate discrete bound states can, in principle, be strongly completely controllable, i.e., the system eigenstates can be guided by the external field to approach arbitrarily close to a target state, which could be theoretically realized by the actions of the creation and annihilation operators on the ground state.     

Structural, elastic and electronic properties and formation energies for hexagonal (W0.5Al0.5)C in comparison with binary carbides WC and Al4C3 from first-principles calculations

First principle calculations have been performed with the purpose to understand the peculiarities of the structural, elastic parameters and electronic properties and interatomic bonding for novel hexagonal carbide (W_0.5Al_0.5)C in comparison with binary phases WC and Al₄C₃. The geometries of all phases were optimized and their structural, elastic parameters and theoretical density were established. Besides, we have evaluated the formation energies (E_form) of W_0.5Al_0.5C for different possible preparation routes (namely for the reactions with the participation of simple substances (metallic W, Al and graphite, binary W or Al carbides and metallic Al and W, or binary W and Al carbides). The results show that the synthesis of the ternary carbide from simple substances is more favorable in comparison with the reactions with participation of W and Al carbides. Moreover, band structures, total and partial densities of states were obtained and analyzed systematically for (W_0.5Al_0.5)C, WC and Al₄C₃ phases in comparison with available theoretical and experimental data. The bonding picture in W_0.5Al_0.5C was described as a mixture of metallic, ionic and covalent contributions with the high anisotropy for the covalent W-C and Al-C bonds, where p-p like Al-C bonds become weaker than p-d like W-C bonds.     

Application of Electron-Shelving Detection via 423 nm Transition in Calcium-Beam Optical Frequency Standard

A new scheme of small compact optical frequency standard based on thermal calcium beam with application of 423 nm shelving detection and sharp-angle velocity selection detection is proposed. Combining these presented techniques, we conclude that a small compact optical frequency standard based on thermal calcium beam will outperform the commercial caesium-beam microwave dock, like the 5071 Cs clock （from Hp to Agilent, now Symmetricom company）, both in accuracy and stability.     

Terahertz Quantum Cascade Laser at 3.39THz

We demonstrate the growth of terahertz quantum cascade laser （THz QCL） by gas source molecular beam epitaxy. X-ray diffraction and cross-sectional transmission electron microscopic measurements show the high crystalline quality of the THz QCL active region, From the cross-sectional transmission electron microscopy image, sharp interfaces are observed and the deduced cascade period thickness is consistent with the result of x-ray diffraction. The test device is lasing at 3.39THz and operating up to lOOK in pulsed mode. At IOK, the maximum output power is greater than 1 mW with a threshold current density of 738 A/cm^2.     

Adsorption and deposition of anthraquinone-2-carboxylic acid on alumina studied by inelastic electron tunneling spectroscopy, infrared reflection absorption spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy

The adsorption state of anthraquinone-2-carboxylic acid (AQ-2-COOH) deposited from acetone solutions (0.01-1.00 mg/ml) on native oxide surfaces of Al films was characterized by inelastic electron tunneling spectroscopy, infrared reflection absorption spectroscopy, and X-ray photoelectron spectroscopy. The oxide was prepared on evaporated Al films at room temperature in an oxygen-dc glow discharge. The morphology of the deposited AQ-2-COOH on the oxide surfaces was observed and analyzed by atomic force microscopy. These surface analyses showed that AQ-2-COOH is adsorbed predominantly as a uniform nanometer-scale film of carboxylate anions on the oxide surfaces deposited from solutions with concentrations lower than or equal to 0.02 mg/ml. It was found that AQ-2-COOH is adsorbed as both a uniform film of anions and as micron-sized particles of neutral molecules with heights of a few tens of nanometers when AQ-2-COOH is deposited from solutions with concentrations higher than 0.02 mg/ml. A comparison of the results obtained by these surface analytical techniques clearly shows the features and advantages of these analytical techniques.     

Instability of Solution of Phase Retrieval in Direct Diffraction Phase-Contrast Imaging with Partially Coherent X-Ray Source

The theoretical model of direct diffraction phase-contrast imaging with partially coherent x-ray source is expressed by an operator of multiple integral. It is presented that the integral operator is linear. The problem of its phase retrieval is described by solving an operator equation of multiple integral. It is demonstrated that the solution of the phase retrieval is unstable. The numerical simulation is performed and the result validates that the solution of the phase retrieval is unstable.     

Modelling the sensitivity of infrared emissivity of magnetic thin films to giant magnetoresistance

The correlation between emissivity and giant magnetoresistance (GMR) in magnetic thin films is investigated at infrared (IR) wavelengths using a thin-film model of emissivity. The sensitivity of emissivity to GMR is shown to depend upon film thickness, and agrees excellently with bulk-material results for films thicker than the material skin depth. However, for films thinner than the skin depth the sensitivity to GMR is shown to weaken. In addition, at mid-to-far IR wavelengths the spectral dependence of the correlation is investigated using a modified Drude-type expression for the refractive index combined with the thin-film model. This is applied to a multilayered GMR material, and the sensitivity of emissivity to GMR is shown to have a similar spectral dependence to that of the magnetorefractive effect. An analytical interpretation in terms of skin depth is also developed at long wavelengths, and shown to agree excellently with thin-film simulations.     

Transformation mechanism of n-butyl terminated Si nanoparticles embedded into Si1−xCx nanocomposites mixed with Si nanoparticles and C atoms

Bright-field transmission electron microscopy (TEM) images, high-resolution TEM (HRTEM) images, and fast-Fourier transformed electron-diffraction patterns showed that n-butyl terminated Si nanoparticles were aggregated. The formation of Si_1−xC_x nanocomposites was mixed with Si nanoparticles and C atoms embedded in a SiO₂ layer due to the diffusion of C atoms from n-butyl termination shells into aggregated Si nanoparticles. Atomic force microscopy (AFM) images showed that the Si_1−xC_x nanocomposites mixed with Si nanoparticles and C atoms existed in almost all regions of the SiO₂ layer. The formation mechanism of Si nanoparticles and the transformation mechanism of n-butyl terminated Si nanoparticles embedded into Si_1−xC_x nanocomposites mixed with Si nanoparticles and C atoms are described on the basis of the TEM, HRTEM, and AFM results. These results can help to improve the understanding of the formation mechanism of Si nanoparticles.     

Saturation and isotope mixing during low-temperature implantations of hydrogen into metals

Deuterons of 10 keV energy and protons with the same mean projected range have been implanted into several metals at a temperature of approximately 35 K and at dose rates of approximately 2 × 10¹⁴ cm^–2 s^–1. The amount of retained deuterium saturates at fluences larger than roughly 2 × 10¹⁸ cm^–2. After implantation of deuterons and subsequent bombardment with protons, the deuteron depth profiles show characteristic double peak structures, which indicate a replacement process. The experimental data are in good agreement with a simple model of local saturation and mixing. The possible implications of this model are discussed.     

High work function of Al-doped zinc-oxide thin films as transparent conductive anodes in organic light-emitting devices

Deposition of Al-doped ZnO (AZO) films with various film thicknesses on glass substrates was performed to investigate the feasibility of using AZO films as anode electrodes in organic light-emitting devices (OLEDs). The electrical resistivity of the AZO films with a 180-nm thickness was 4.085 × 10⁻² Ω cm, and the average optical transmittance in the visible range was 80.2%. The surface work function for the AZO films, determined from the secondary electron emission coefficients obtained with a focused ion beam, was as high as 4.62 eV. These results indicate that AZO films grown on glass substrates hold promise for potential applications as anode electrodes in high-efficiency OLEDs.     

The effect of Ehrlich-Schwoebel step-edge barrier on the formation of self-organized Si nanodots by ion-sputter erosion

The ion flux dependence of the self-organized Si nanodots induced by 1.5 keV Ar⁺ ion sputter erosion has been studied. It shows that for the regime with ion flux >∼280 μA/cm², the currently adopted Bradley-Harper (BH) model, which is incorporated in a dynamic continuum equation holds valid. However, for ion flux <∼280 μA/cm², the measured dot size and surface roughness deviate drastically from the BH model. To interpret the data for this lower ion flux regime, the effect of the Ehrlich-Schwoebel (ES) step-edge barrier was introduced into the continuum equation. A consistency between the calculated and the experimental results was reached, furthermore, a reasonable trend was found, that is, the effective ES diffusion decreases steadily with the increasing ion flux, and at ∼280 μA/cm², it became negligibly small.     

The photoacoustic spectroscopic investigations of the surface preparation of ZnSe crystals with the use of the optimization methods

This paper shows results of the photoacoustic (PA) spectral studies, with the microphone detection, of a series of ZnSe crystals with differently prepared surfaces. All samples exhibited the surface absorption connected with defects states located on their surfaces. The quality of the surface preparation is expressed by the surface absorption coefficient spectra of the samples times the thickness of a damaged layer. In this paper both theoretical and experimental photoacoustic amplitude and phase spectra as also the corresponding computed surface and volume optical absorption coefficient spectra of the samples with differently prepared surfaces are presented and discussed. The procedure of computations of the volume and surface absorption spectra with the use of the optimization method is presented in the paper too.     

Manifestation of MnCl2 fillers incorporated into the polymer matrices in their dielectric properties

Polyethyl methacrylate (PEMA) films filled with different mass fractions of MnCl₂ were prepared using a casting method. The structural and electrical properties were studied. The filling content dependence of certain IR absorption bands was correlated with the obtained physical parameter characterizing the other properties. DC electrical resistivity (ρ) was measured in the temperature range 340-420 K for PEMA films filled with MnCl₂ fillers. An intrachain one-dimensional interpolaron hopping mechanism was assumed to interpret the electrical conduction. AC conductivity behavior of all the prepared samples was investigated over the frequency range (42-5M) Hz and under different isothermal stablilization in the temperature range 300-423 K. It suggested that the hopping mechanism might be playing an important role in the conduction process, in low temperature regime. The values of σ₀, A, and S satisfying the suitable fit of the conductivity data, as well as the corresponding (σ_DC).     

Variable-coefficient higher-order nonlinear Schrödinger model in optical fibers: Variable-coefficient bilinear form,Bäcklund transformation,brightons and symbolic computation

Symbolically investigated in this Letter is a variable-coefficient higher-order nonlinear Schrödinger (vcHNLS) model for ultrafast signal-routing, fiber laser systems and optical communication systems with distributed dispersion and nonlinearity management. Of physical and optical interests, with bilinear method extend, the vcHNLS model is transformed into a variable-coefficient bilinear form, and then an auto-Bäcklund transformation is constructed. Constraints on coefficient functions are analyzed. Potentially observable with future optical-fiber experiments, variable-coefficient brightons are illustrated. Relevant properties and features are discussed as well. Bäcklund transformation and other results of this Letter will be of certain value to the studies on inhomogeneous fiber media, core of dispersion-managed brightons, fiber amplifiers, laser systems and optical communication links with distributed dispersion and nonlinearity management.