Dynamics of photon–photon entanglement in a bimodal nonlinear nanocavity

The photon–photon entanglement dynamics in a bimodal nanocavity, filled with a centrosymmetric nonlinear medium, is studied. In the present study, we have included the first and third order susceptibilities, giving rise to linear and the Kerr-type couplings. With no restrictions placed on the relative strength of these effects, we prove that the corresponding Hamiltonian is block-diagonal, each with ever-growing dimensions. We then show that, depending upon the initial total photon number, one needs to diagonalize a specific low-dimensional block, leading to the time evolution operator. Consequently, the time-evolution of the von Neumann entropy, as a measure of entanglement, is determined. From an analysis of the von Neumann entropy, we show that the entanglement exhibits oscillations, with plateaus, whose characteristics (period, duration, … ) strongly depend upon the strength of third order susceptibility. Moreover, it is shown that the entanglement is enhanced as the linear coupling is increased. The effect of detuning between photon's frequencies is also discussed.     

Gas chromatographic technique for determination of Irgafos 168 in polyolefin samples after conversion to the related phenolic compound by saponification

A gas chromatographic technique is reported for the determination of a secondary antioxidant, Irgafos 168, in polymeric samples. Irgafos 168 [tris(2,4-di-tert-butyl phenyl)phosphite] is extracted by dissolution/precipitation, saponified to 2,4-di-tert-butyl phenol by refluxing in the presence of methanolic potassium hydroxide, and determined by gas chromatography-flame ionization detection. The method’s repeatability is good, and the relative standard deviation is 7.5% (between runs) and 15.5% (between days). This method was applied to the determination of Irgafos 168 in commercial polymers, and the obtained results were in relatively good agreement with those obtained by the previously reported spectrophotometric method. Correspondence: Mir Ali Farajzadeh, Department of Chemistry, Faculty of Science, Urmia University, Urmia, Iran     

Thermal entanglement of a two-level atom and bimodal photons in a Kerr nonlinear coupler

In this paper thermally induced entanglement between a two-level atom and photons inside a bimodal nonlinear coupler is studied. The interaction occurs in the presence of a centrosymmetric medium which couples the two photonic modes via the first and third order susceptibilities. Such effects on the atom–photons interaction, however, are assumed negligible so that the linear Jaynes–Cummings model applies. It is further assumed that the coupler is held at a temperature T$T$, so that each of the combined atom–photon states, with a definite, T$T$ dependent, probability, is present. The partially transposed density matrix and, consequently, the negativity, as a measure of entanglement, are determined as functions of temperature. The negativity so calculated shows that the system of a two-level atom and photons is separable at zero temperature, becomes more entangled, reaching the maximal at a certain temperature and asymptotically disentangles. Effect of medium characteristics on such behavior is also discussed.     

Enhanced lithium electrochemical performance and optical properties of CeO<Subscript>2</Subscript>–SnO<Subscript>2</Subscript> nanocomposite thin films by transition metal (TM: Ni,Mn, and Co) doping

Undoped and transition metal (TM: Ni, Mn, Co)-doped CeO₂–SnO₂ nanocomposite thin films were prepared by sol-gel dip coating (SGDC) technique. The grazing incidence X-ray diffraction (GIXRD) patterns indicated that CeO₂–SnO₂ film has a cubic structure of CeO₂ and the crystallinity deteriorated with incorporation of dopant. The scanning electron microscopy (SEM) and atomic force microscopy (AFM) images showed that the surface morphology of the films was affected by TM incorporation. The surface roughness and fractal dimensions of CeO₂–SnO₂ films increased with doping. The average transmittance of CeO₂–SnO₂ thin film is found nearly 80% in the visible region and increased with doping. The absorption edge revealed a blue shift toward shorter wavelengths after incorporation of TM ions. The compositional dependence of optical parameters such as refractive index, extinction coefficient, and optical conductivity were also investigated. Cyclic voltammetry measurements showed that ion storage capacity was decreased significantly with increasing scan rate. The undoped and doped CeO₂–SnO₂ films showed good reversible cycle of intercalation/deintercalation of Li⁺ ions. The ion storage capacity and electrochemical stability were enhanced with transition metal doping. The Mn-doped CeO₂–SnO₂ composite thin film had better ion storage capacity rather than other samples due to its special porous morphology. The Li diffusion toward electrode surface was described in terms of self-similar fractal dimension. A quenching in blue-green photoluminescence (PL) intensity of CeO₂–SnO₂ films was occurred by transition metal doping.

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Von Neumann entropy in a Rashba-Dresselhaus nanodot; dynamical electronic spin-orbit entanglement

The main purpose of the present article is to report the characteristics of von Neumann entropy, thereby, the electronic hybrid entanglement, in the heterojunction of two semiconductors, with due attention to the Rashba and Dresselhaus spin-orbit interactions. To this end, we cast the von Neumann entropy in terms of spin polarization and compute its time evolution; with a vast span of applications. It is assumed that gate potentials are applied to the heterojunction, providing a two dimensional parabolic confining potential (forming an isotropic nanodot at the junction), as well as means of controlling the spin-orbit couplings. The spin degeneracy is also removed, even at electronic zero momentum, by the presence of an external magnetic field which, in turn, leads to the appearance of Landau states. We then proceed by computing the time evolution of the corresponding von Neumann entropy from a separable (spin-polarized) initial state. The von Neumann entropy, as we show, indicates that electronic hybrid entanglement does occur between spin and two-dimensional Landau levels. Our results also show that von Neumann entropy, as well as the degree of spin-orbit entanglement, periodically collapses and revives. The characteristics of such behavior; period, amplitude, etc., are shown to be determined from the controllable external agents. Moreover, it is demonstrated that the phenomenon of collapse-revivals’ in the behavior of von Neumann entropy, equivalently, electronic hybrid entanglement, is accompanied by plateaus (of great importance in quantum computation schemes) whose durations are, again, controlled by the external elements. Along these lines, we also make a comparison between effects of the two spin-orbit couplings on the entanglement (von Neumann entropy) characteristics. The finer details of the electronic hybrid entanglement, which may be easily verified through spin polarization measurements, are also accreted and discussed. The novel results of the present article, with potent applications in the field of quantum information processing, provide a deeper understanding of the electronic von Neumann entropy and hybrid entanglement that occurs in two-dimensional nanodots.     

The reduction of rotational ambiguity in soft-modeling by introducing hard models

Rotational ambiguity is a major problem in the application of soft-modeling analysis to a variety of multivariate mixture resolution problems and particularly important in the analysis of kinetic data. Soft-modeling analyses rely on constraints that restrict the concentration profiles and/or the spectral responses of all components. The main goal of this work is to demonstrate how a hard-modeling constraint on concentration profiles drastically decreases the extent of the rotational ambiguity. Therefore, in the present paper the discussion is focused on systems in which hard-modeling information is available. The results of simulated examples reveal that the utilized hard constraint decreases the rotational ambiguity in estimated concentration profile even components that do not take part in the explicit model. In addition, the rate constant of known reaction is determined in this method.     

Design of a fast convergent backpropagation algorithm based on optimal control theory

The main contribution of this paper is using optimal control theory for improving the convergence rate of backpropagation algorithm. In the proposed approach, the learning algorithm of backpropagation is modeled as a minimum time control problem in which the step-size of its learning factor is considered as the input of this model. In contrast to the traditional backpropagation, learning algorithms which select the step-size by trial and error, it is selected adaptively based on optimal control criterion. The effectiveness of the proposed algorithm is evaluated in two simulations: XOR and 3-bit parity. In both simulation examples, the proposed algorithm outperforms well in speed and the ability to escape from local minima.     

A theoretical practice on grazing‐exit energy dispersive X‐ray spectroscopy as a surface analysis strategy to investigate BiVO4 nano‐films

In the current work, a thin film of bismuth vanadate was defined over a silicon substrate, and a calculative Monte Carlo approach was followed to achieve the best grazing‐exit angle to acquire compositional data from top few nanometers of surface. This strategy is very beneficial in order to increase X‐ray signals originated from surface and diminish the background X‐ray signals started off from the substrate. In this regard, grazing‐exit energy dispersive X‐ray spectroscopy can be considered as an accessible and economical analytical tool to investigate thin films and nano‐layers. The major advantage of this method is that just by applying a re‐arrangement in a scanning electron microscope, it can be used to study compositional properties of thin layers. In this contribution, a theoretical approach using Monte Carlo models was used to simulate the behavior of electron beams impinging onto BiVO₄ nano‐layers with thickness of 50 nm and electron trajectories inside the film. Characteristic X‐rays and spatial energy distribution of the backscattered electrons were also calculated. Under grazing‐exit angle of around 0.5°, the best surface signal/background noise ratio was achieved. Copyright © 2014 John Wiley & Sons, Ltd.