Showing papers in "European Physical Journal D in 2012"

UKRmol: a low-energy electron- and positron-molecule scattering suite

Abstract: We describe the UK computational implementation of the R-matrix method for the treatment of electron and positron scattering from molecules. Recent developments in the UKRmol suite are detailed together with the collision processes it is enabling us to treat.

Scheme for n phase gates operation and one-step preparation of highly entangled cluster state

Abstract: In the system with superconducting quantum interference devices (SQUIDs) in a cavity, we propose a scheme for simultaneous implementing n phase gates and one step preparing the highly entangled cluster states based on the two-channel Raman interaction. In our scheme, the system is independent to the photon number of the cavity field, the cavity field can be initially in an arbitrary state, which is convenient for the experimental operation. The n phase gates operation and the cluster state generation are realized by using only the two lower flux states of the SQUID and the excited state would not be excited so that the influence of the decoherence due to spontaneous emission of the SQUID’s levels is possible to minimize. More importantly, the operation time of the phase gates is independent of the number n of the qubits. Finally, the experimental feasibility is also discussed in detail.

Atmospheric-pressure cold plasma treatment of contaminated fresh fruit and vegetable slices: inactivation and physiochemical properties evaluation

Abstract: A direct-current, atmospheric-pressure air cold plasma microjet (PMJ) was applied to disinfect Salmonella directly deposited on fresh fruit and vegetable slices. Effective inactivation was achieved on sliced fruit and vegetables after 1 s plasma treatment. The physiochemical properties of the slices, such as water content, color parameters, and nutritional content were monitored before and after plasma treatment. It was found that the physiochemical properties changes caused by the plasma were within an acceptable range. Reactive oxygen species, which are believed to be the major bactericidal agents in the plasma, were detected by electron spin resonance spectroscopy and optical emission spectroscopy.

Absolute OH density determination by laser induced fluorescence spectroscopy in an atmospheric pressure RF plasma jet

Abstract: In this paper, the ground state OH density is measured in high pressure plasma by laser-induced fluorescence (LIF) spectroscopy. The OH density determination is based on the simulation of the intensity fraction of fluorescence from the laser-excited level of OH (A) in the total detected LIF signal. The validity of this approach is verified in an atmospheric pressure Ar + H2O plasma jet sustained by a 13.56 MHz power supply. The transition line P1 (4) from OH (A,v′ = 1,J′ = 3) → OH (X,v′′ = 0,J′′ = 4) is used for the LIF excitation. The absolute OH density is determined to be 2.5 × 1019 m-3 at 1 mm away from the jet nozzle. It corresponds to a dissociation of 0.06% of the water vapor in the working gas. Different mechanisms of OH (X) production in the core of the plasma jet are discussed and analyzed.

Light with orbital angular momentum interacting with trapped ions

Abstract: We study the interaction of light beams carrying angular momentum with a single, trapped and well localized ion. We provide a detailed calculation of selection rules and excitation probabilities for quadrupole transitions. The results show the dependencies on the angular momentum and polarization of the laser beam as well as the direction of the quantization magnetic field. In order to optimally observe the specific effects, focusing the angular momentum beam close to the diffraction limit is required. We discuss a protocol for examining experimentally the effects on the S1/2 to D5/2 transition using a 40Ca+ ion. Various applications and advantages are expected when using light carrying angular momentum: in quantum information processing, where qubit states of ion crystals are controlled, parasitic light shifts could be avoided as the ion is excited in the dark zone of the beam at zero electric field amplitude. Such interactions also open the door to high dimensional entanglement between light and matter. In spectroscopy one might access transitions which have escaped excitation so far due to vanishing transition dipole moments.

QCT-based vibrational collisional models applied to nonequilibrium nozzle flows

Abstract: Thermal and chemical nonequilibrium effects are investigated in hypersonic nozzle expanding flows by means of vibrational collisional models. The rate coefficients for rovibrational dissociation and excitation are provided by two chemical databases for the N + N2 system recently developed at NASA Ames Research Center and the University of Bari. Vibrationally averaged rate coefficients for N + N2 collisions are computed based on the hypothesis of equilibrium between translational and rotational modes. N2 + N2 collisions are also considered based on literature data. Inviscid and quasi 1D governing equations are discretized in space by means of a finite volume method. A fully implicit time integration method is applied to obtain steady state solutions. Results show that, for both N + N2 and N2 + N2 collision dominated flows, the populations of vibrational levels deviate from a Boltzmann distribution. An accurate investigation of vibrational level dynamics shows the different behavior of low and high-lying states. Comparison against experimental data acquired at the EAST facility of NASA Ames Research Center demonstrate good agreement between the computed and experimental results.

Experimental g factor of hydrogenlike silicon-28

Abstract: The g factor of the electron bound in hydrogenlike 28Si13+ has been measured to 10 significant digits. The value agrees very well with bound-state quantum-electrodynamical calculations and represents to date the most stringent test of the theory. The experiment uses a single ion confined in a triple Penning trap. Here we present details of the setup, the experimental procedure and the data evaluation.

Cross section data sets for electron collisions with H2, O2, CO, CO2, N2O and H2O

Abstract: We review earlier cross section data sets for electron-collisions with H2, O2, CO, CO2, H2O and N2O, updated here by experimental results for their electronic states. Based on our recent measurements of differential cross sections for the electronic states of those molecules, integral cross sections (ICSs) are derived by applying a generalized oscillator strength analysis and then assessed against theory (BEf-scaling [Y.-K. Kim, J. Chem. Phys. 126, 064305 (2007)]). As they now represent benchmark electronic state cross sections, those ICSs for the above molecules are added into the original cross section sets taken from the data reviews for H2, O2, CO2 and H2O (the Itikawa group), and for CO and N2O (the Zecca group).

Spatial Schmidt modes generated in parametric down-conversion

Abstract: This paper presents the general spatial Schmidt decomposition of two-photon fields generated in spontaneous parametric down-conversion (SPDC). It discusses in particular the separation of the radial and azimuthal degrees of freedom, the role of projection in modal analysis, and the benefits of collinear phase mismatch. The paper is written in a review style and presents a wealth of numerical results. It aims at emphasising the physics beyond the mathematics, through discussions and graphical representations of key results. The two main conclusions of the paper are the finding of a better law to describe the effective dimensionality of the spatial part of the total Hilbert space and a possible novel feature of the radial Schmidt modes.

Enhanced frequency upconversion in Er 3+-doped sodium lead tellurite glass containing silver nanoparticles

Abstract: A series of silver nanoparticle embedded in erbium-doped tellurite glasses were synthesized using a one step melt-quenching method. Density and refractive index of glasses were measured. Thermal and optical characterizations were performed and plasmon bands of elliptical nanoparticles were observed. An enhancement of green (525 and 550 nm) and red (632 nm) lines in luminescence spectra of Er3+-doped silver-embedded tellurite glass was recorded and explained by energy transfer mechanism from silver nanoparticles to erbium ion in addition to enhanced local field in vicinity of metallic nanoparticles in the glass. The presence of nanoparticles was confirmed by transmission electron microscopy imaging and reduction of silver ions to silver neutral particles discussed through the redox potential estimation in probable reactions. Silver-erbium co-doped tellurite glass exhibits strong novel optical properties which nominate it as the promising glass for laser, color displays, and photonic applications.

Wave-particle duality of solitons and solitonic analog of the Ramsauer-Townsend effect

Abstract: We show that the scaling symmetry breaking in soliton scattering reveals the hidden role of the soliton self-interaction (“binding”) energy and its dramatic impact on the wave-particle duality of solitons. Solitonic analog of the de Broglie wavelength and phenomenon similar to the Ramsauer-Taunsend effect can be discovered for Schrodinger solitons.

Electron-scale electrostatic solitary waves and shocks: the role of superthermal electrons

Abstract: The propagation of electron-acoustic solitary waves and shock structures is investigated in a plasma characterized by a superthermal electron population A three-component plasma model configuration is employed, consisting of inertial (“cold”) electrons, inertialess κ (kappa) distributed superthermal (“hot”) electrons and stationary ions A multiscale method is employed, leading to a Korteweg-de Vries (KdV) equation for the electrostatic potential (in the absence of dissipation) Taking into account dissipation, a hybrid Korteweg-de Vries-Burgers (KdVB) equation is derived Exact negative-potential pulse- and kink-shaped solutions (shocks) are obtained The relative strength among dispersion, nonlinearity and damping coefficients is discussed Excitations formed in superthermal plasma (finite κ) are narrower and steeper, compared to the Maxwellian case (infinite κ) A series of numerical simulations confirms that energy initially stored in a solitary pulse which propagates in a stable manner for large κ (Maxwellian plasma) may break down to smaller structures or/and to random oscillations, when it encounters a small-κ (nonthermal) region On the other hand, shock structures used as initial conditions for numerical simulations were shown to be robust, essentially responding to changed in the environment by a simple profile change (in width)

Quantum entanglement in exactly soluble atomic models: the Moshinsky model with three electrons, and with two electrons in a uniform magnetic field

Abstract: We investigate the entanglement-related features of the eigenstates of two exactly soluble atomic models: a one-dimensional three-electron Moshinsky model, and a three-dimensional two-electron Moshinsky system in an external uniform magnetic field. We analytically compute the amount of entanglement exhibited by the wavefunctions corresponding to the ground, first and second excited states of the three-electron model. We found that the amount of entanglement of the system tends to increase with energy, and in the case of excited states we found a finite amount of entanglement in the limit of vanishing interaction. We also analyze the entanglement properties of the ground and first few excited states of the two-electron Moshinsky model in the presence of a magnetic field. The dependence of the eigenstates’ entanglement on the energy, as well as its behaviour in the regime of vanishing interaction, are similar to those observed in the three-electron system. On the other hand, the entanglement exhibits a monotonically decreasing behavior with the strength of the external magnetic field. For strong magnetic fields the entanglement approaches a finite asymptotic value that depends on the interaction strength. For both systems studied here we consider a perturbative approach in order to shed some light on the entanglement’s dependence on energy and also to clarify the finite entanglement exhibited by excited states in the limit of weak interactions. As far as we know, this is the first work that provides analytical and exact results for the entanglement properties of a three-electron model.

Structure and thermal stability of AgCu chiral nanoparticles

Abstract: The structure and thermal stability of AgCu core-shell chiral nanoparticles is investigated by means of global optimization searches and molecular-dynamics simulations within an atomistic model. The most energetically stable structures are searched for depending on the number N Ag of Ag atoms in the outer shell. Both icosahedral and C5 symmetry structures are considered. The thermal stability of the structures is studied for magic sizes and compositions by analyzing the melting transition. It is found that chiral shells are the most favourable in a wide range of N Ag and that the structures present a notable thermal stability.

Application of the time-dependent close-coupling approach to few-body atomic and molecular ionizing collisions

Abstract: We review the recent progress made in applying the time-dependent close-coupling approach to ionizing collisions of electrons, photons, and ions with small atoms and molecules. The last twenty years have seen a proliferation of non-perturbative approaches applied to fundamental atomic and molecular scattering processes. Such processes form the building blocks of describing the dynamics of plasmas over a wide range of temperatures and densities, and also provide insight into the long-range Coulomb interactions between charged particles. Studies of the few-body Coulomb problem presented in electron, photon, or ion-impact ionization of small atoms and molecules, by direct solution of the time-dependent Schrodinger equation, are particularly useful because the complicated three-body boundary conditions of more than one continuum particle in a Coulomb potential are not required. With the continuing growth and increasing availability of high-performance computing resources, such methods can now be applied to a wide variety of scattering processes. The recent progress made using such a time-dependent approach is described in this colloquium. In this paper, we focus on the recent results obtained for one-, two-, and three-electron systems, thus building on a previous review of the time-dependent close-coupling method [M.S. Pindzola et al., J. Phys. B 40, R39 (2007)], which also described the application to multi-electron targets.

Continuous deformations of the Grover walk preserving localization

Abstract: The three-state Grover walk on a line exhibits the localization effect characterized by a non-vanishing probability of the particle to stay at the origin. We present two continuous deformations of the Grover walk which preserve its localization nature. The resulting quantum walks differ in the rate at which they spread through the lattice. The velocities of the left and right-traveling probability peaks are given by the maximum of the group velocity. We find the explicit form of peak velocities in dependence on the coin parameter. Our results show that localization of the quantum walk is not a singular property of an isolated coin operator but can be found for entire families of coins.

Light-induced anisotropy of atomic response: prospects for emission spectrum control

Abstract: We present the quantum mechanical theory of the nonlinear atomic response in a strong laser field. The proposed approach provides the self consistent description of the atomic response both in the long (THz) and the short (XUV) wavelength regions. At the subrelativistic intensity of a laser pulse, our approach is valid for the arbitrary ratio between the laser and the intra-atomic field strengths. Instead of the traditional basis of the “free atom” eiegenfunctions, the basis of eiegenfunctions of the boundary value problem for “the atom in an external field” is used to calculate the matrix elements of the quantum mechanical operators. In this case the matrix elements of the generalized momentum operator and the Hamiltonian of the time-dependent Schrodinger equation are directly related with the experimentally measured dipole matrix elements and the energy spectrum of a free atom. The response of the atomic argon in the two-color laser field of arbitrary polarized components has been calculated numerically. The results of computer simulations show that the efficiency of the atomic response depends non-monotonically on the angle between the polarization vectors of the laser pulses. We also show that the most effective mechanism of THz emission in the two-color laser field appears mainly due to the atomic non-linearity, and not to the plasma non-linearities playing the dominant role in the case of the monochromatic laser field. The predictions of our theory coincide with the numerical and experimental results. This fact gives us a reliable base to provide the straightforward explanation of the observed dependencies, and to propose the methods of enhancement of efficiency of the nonlinear transformations both in the long and short wavelength spectral regions.

Analytical study on the self-healing property of Bessel beam

Abstract: With the help of Babinet principle, an analytical expression for the self-healing of Bessel beam is derived by using the Gaussian absorption function to describe the obstacle. Based on the analytical expression, the self-healing properties of Bessel beam are studied. It shows that Bessel beam has the ability to reconstruct its beam shape disturbed by an obstacle. However, during the self-healing process, not only the intensity of the beam behind the obstacle but also the other part will be affected by the obstruction. Meanwhile, the highlight spot, which intensity is larger than that without the obstacle will appear, and the size and strength of the highlight spot is determined by the size of the obstacle. From the change of Poynting vector and Babinet principle, the physical interpretations for the self-healing ability, the effects of the obstruction on the other part and the appearance of highlight spot are given.

Generation of a wave packet tailored to efficient free space excitation of a single atom

Abstract: We demonstrate the generation of an optical dipole wave suitable for the process of efficiently coupling single quanta of light and matter in free space. We employ a parabolic mirror for the conversion of a transverse beam mode to a focused dipole wave and show the required spatial and temporal shaping of the mode incident onto the mirror. The results include a proof of principle correction of the parabolic mirror’s aberrations. For the application of exciting an atom with a single photon pulse, we demonstrate the creation of a suitable temporal pulse envelope. We infer coupling strengths of 89% and success probabilities of up to 87% for the application of exciting a single atom for the current experimental parameters.

Collective excitations in the electron energy loss spectra of C-60

Abstract: The results of a joint experimental and theoretical investigation of the collective excitations in the energy loss spectra of the C60 fullerene are presented. A variation of the shape of the electron energy loss spectrum has been observed experimentally as the scattering angle increases. This variation is described within the frame of a new theoretical model which treats the fullerene as a spherical shell of a finite width and accounts for the two modes of the surface plasmon and for the volume plasmon as well. It is shown that at small angles the inelastic scattering cross section is determined mostly by the excitation of the symmetric mode of the surface plasmon, while at larger angles the excitation of the antisymmetric surface and volume plasmons becomes prominent.

Resonant charge transfer at dielectric surfaces

Abstract: We report on the theoretical description of secondary electron emission due to resonant charge transfer occurring during the collision of metastable N2(3Σ+ u ) molecules with dielectric surfaces. The emission is described as a two step process consisting of electron capture to form an intermediate shape resonance N2 -(2Π g ) and subsequent electron emission by decay of this ion, either due to its natural life time or its interaction with the surface. The electron capture is modeled using the Keldysh Green’s function technique and the negative ion decay is described by a combination of the Keldysh technique and a rate equation approach. We find the resonant capture of electrons to be very efficient and the natural decay to be clearly dominating over the surface-induced decay. Secondary electron emission coefficients are calculated for Al2O3, MgO, SiO2, and diamond at several kinetic energies of the projectile. With the exception of MgO the coefficients turn out to be of the order of 10-1 over the whole range of kinetic energies. This rather large value is a direct consequence of the shape resonance acting as a relay state for electron emission.

The energy eigenvalues of the Kratzer potential in the presence of a magnetic field

Abstract: Two dimensional solution of the Schrodinger equation for the Kratzer potential with and without the presence of a constant magnetic field is investigated within the framework of the asymptotic iteration method. The energy eigenvalues are analytically obtained for the absence of the magnetic field case. However, in the presence of a constant magnetic field, the energy eigenvalues are calculated numerically using the same method. The results obtained by using different Larmor frequencies and potential parameters are compared with the results of the absence of the magnetic field case (ω L = 0). Effect of the magnetic field on the energy eigenvalues of the Kratzer potential is precisely presented.

Increase in the beam intensity of the linac-based slow positron beam and its application at the Slow Positron Facility, KEK

Abstract: Recent developments of the Slow Positron Facility at the Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK) are reported. We have modified the converter/moderator assembly for slow positron beam production, yielding an increase of an order of magnitude in the intensity of the beam. The first observation of the photodetachment of the positronium negative ion (Ps−), and the installation of a reflection high-energy positron diffraction (RHEPD) station and the initial data obtained are reported.

Information leak in Liu et al.’s quantum private comparison and a new protocol

Abstract: In a recent paper [W. Liu, Y.B. Wang, Z.T. Jiang, Opt. Commun. 284, 3160 (2011)], a quantum private comparison (QPC) protocol based on W states was presented. Compared to the previous QPCs, the protocol is promising for that it can prevent the comparison result from revealing to the third party. However, this study point out that a flaw of information leak is existent in the protocol. And a new QPC which can avoid the flaw and has higher efficiency is proposed in this paper.

Ni nanoparticle catalyzed growth of MWCNTs on Cu NPs @ a-C:H substrate

Abstract: NiCu NPs @ a-C:H thin films with different Cu content were prepared by co-deposition by RF-sputtering and RF-plasma enhanced chemical vapor deposition (RF-PECVD) from acetylene gas and Cu and Ni targets. The prepared samples were used as catalysts for growing multi-wall carbon nanotubes (MWCNTs) from liquid petroleum gas (LPG) at 825 °C by thermal chemical vapor deposition (TCVD). By addition of Cu NPs @ a-C:H thin layer as substrate for Ni NPs catalyst, the density of the grown CNTs is greatly enhanced in comparison to bare Si substrate. Furthermore the average diameter of the grown CNTs decreases by decreasing of Cu content of Cu NPs @ a-C:H thin layer. However Cu NPs @ a-C:H by itself has no catalytic property in MWCNTs growth. Morphology and electrical and optical properties of Cu NPs @ a-C:H thin layer is affected by Cu content and each of them is effective parameter on growth of MWCNTs based on Ni NPs catalyst. Moreover, adding of a low amount of Ni NPs doesn’t vary optical, electrical and morphology properties of Cu NPs @ a-C:H thin layer but it has a profound effect on its catalytic activity. Finally the density and diameter of MWCNTs can be optimized by selection of the Cu NPs @ a-C:H thin layer as substrate of Ni NPs.

Applications of a simplified bilinear method to ion-acoustic solitary waves in plasma

Abstract: In this paper, we propose a computational method for nonlinear partial differential equations modeling ion-acoustic waves as well as dusty plasmas in laboratory and space sciences. Many types of solitary waves including soliton solutions, N-soliton solutions and singular N-soliton solutions are derived. The characteristic line method and graphical analysis are applied to discuss the solitonic propagation and collision, including the bidirectional solitons and elastic interactions. Furthermore, the effects of inhomogeneities of media and nonuniformities of boundaries, depicted by the variable coefficients, on the soliton behavior are discussed.

Quantum discord evolution of three-qubit states under noisy channels

Abstract: We investigated the dissipative dynamics of quantum discord for correlated qubits under Markovian environments. The basic idea in the present scheme is that quantum discord is more general, and possibly more robust and fundamental, than entanglement. We provide three initially correlated qubits in pure Greenberger-Horne-Zeilinger (GHZ) or W state and analyse the time evolution of the quantum discord under various dissipative channels such as: Pauli channels σ x , σ y , and σ z , as well as depolarising channels. Surprisingly, we find that under the action of Pauli channel σ x , the quantum discord of GHZ state is not affected by decoherence. For the remaining dissipative channels, the W state is more robust than the GHZ state against decoherence. Moreover, we compare the dynamics of entanglement with that of the quantum discord under the conditions in which disentanglement occurs and show that quantum discord is more robust than entanglement except for phase flip coupling of the three-qubits system to the environment.

Quantum Fisher information for a single qubit system

Abstract: The Fisher information is used for quantum state estimation and considered as a physical resource associated with various quantities. The concept of Fisher information in terms of the atomic density operator is introduced. We give the correlation between the Fisher information and quantum entanglement during the time evolution for a trapped ion in laser field. The effect of the initial state setting on the classical Fisher information and quantum Fisher information is examined. The results show that the Fisher information is efficacious tool to study single qubit dynamics as an indicator of entanglement under certain conditions. Our observations may have important implications in exploiting this quantity in quantum information processing and transmission.

Layers of cold dipolar molecules in the harmonic approximation

Abstract: We consider the N-body problem in a layered geometry containing cold polar molecules with dipole moments that are polarized perpendicular to the layers. A harmonic approximation is used to simplify the Hamiltonian and bound state properties of the two-body inter-layer dipolar potential are used to adjust this effective interaction. To model the intra-layer repulsion of the polar molecules, we introduce a repulsive inter-molecule harmonic potential and discuss how its strength can be related to the real dipolar potential. However, to explore different structures with more than one molecule in each layer, we treat the repulsive harmonic strength as an independent variable in the problem. Single chains containing one molecule in each layer, as well as multi-chain structures in many layers are discussed and their energies and radii determined. We extract the normal modes of the various systems as measures of their volatility and eventually of instability, and compare our findings to the excitations in crystals. We find modes that can be classified as either chains vibrating in phase or as layers vibrating against each other. The former correspond to acoustic and the latter to optical phonons. For the acoustic modes, our model predicts a smaller sound speed than one would naively get from expansion of the dipolar potential to second order around the origin. Instabilities can occur for large intra-layer repulsion and produce diverging amplitudes of molecules in the outer layers, and our model predicts how the breakup takes places. Lastly, we consider experimentally relevant regimes to observe the structures. The harmonic model considered here predicts that for the multi-layer systems under current study chains with one molecule in each layer are always bound whereas two chains comprised of two molecules in each layer will not be bound. However, since realistic systems have external confinement prevention the molecules from escaping to infinity, we still expect the unstable modes to show up as resonances in the dynamics.

Investigation of the SiC thin films synthetized by Thermionic Vacuum Arc method (TVA)

Abstract: Thermionic Vacuum Arc method (TVA) was used for the first time to prepare SiC thin films. This method is very suitable for deposition of high purity thin films with compact structure and extremely smooth in vacuum conditions. The nanocomposites were investigated using Transmission Electron Microscopy (TEM) analyses provided with HR-TEM and SAED facilities. The structure of the films can be indexed as following three forms: cubic structure of SiC (F4-3m) a = 0.4348 nm, cubic Si (Fd3m) a = 0.54307 nm and graphite (P63/mmc) a = 0.2456 nm; c = 0.6696 nm. The morphology, topography, wettability and wear properties were also performed by SEE system and by Raman Spectroscopy, increasing the interest for emerging applications.