Entanglement induced by a single-mode heat environment

A thermal field, which frequently appears in problems of decoherence, provides us with minimal information about the field. We study the interaction of the thermal field and a quantum system composed of two qubits and find that such a chaotic field with minimal information can nevertheless entangle qubits that are prepared initially in a separable state. This simple model of a quantum register interacting with a noisy environment allows us to understand how memory of the environment affects the state of a quantum register.

Strong parallel magnetic field effects on the hydrogen molecular ion

Equilibrium distances, binding energies and dissociation energies for the ground and low-lying states of the hydrogen molecular ion in a strong magnetic field parallel to the internuclear axis are calculated and refined, by using the two- dimensional pseudospectral method. High-precision results are presented for the binding energies over a wider field regime than already given in the literature (Kravchenko and Liberman 1997 Phys. Rev. A 55 2701). The present work removes a long- standing discrepancy for the R-eq value in the 1sigma(u) state at a field strength of 1.0 x 10(6) T. The dissociation energies of the antibonding 1pi(g) state induced by magnetic fields are determined accurately. We have also observed that the antibonding 1pi(g) potential energy curve develops a minimum if the field is sufficiently strong. Some unreliable results in the literature are pointed out and discussed. A way to efficiently treat vibrational processes and coupling between the nuclear and the electronic motions in magnetic fields is also suggested within a three-dimensional pseudospectral scheme.

A reactive force field simulation of liquid-liquid phase transitions in phosphorus

A force field model of phosphorus has been developed based on density functional (DF) computations and experimental results, covering low energy forms of local tetrahedral symmetry and more compact (simple cubic) structures that arise with increasing pressure. Rules tailored to DF data for the addition, deletion, and exchange of covalent bonds allow the system to adapt the bonding configuration to the thermodynamic state. Monte Carlo simulations in the N-P-T ensemble show that the molecular (P-4) liquid phase, stable at low pressure P and relatively low temperature T, transforms to a polymeric (gel) state on increasing either P or T. These phase changes are observed in recent experiments at similar thermodynamic conditions, as shown by the close agreement of computed and measured structure factors in the molecular and polymer phases. The polymeric phase obtained by increasing pressure has a dominant simple cubic character, while the polymer obtained by raising T at moderate pressure is tetrahedral. Comparison with DF results suggests that the latter is a semiconductor, while the cubic form is metallic. The simulations show that the T-induced polymerization is due to the entropy of the configuration of covalent bonds, as in the polymerization transition in sulfur. The transition observed with increasing P is the continuation at high T of the black P to arsenic (A17) structure observed in the solid state, and also corresponds to a semiconductor to metal transition. (C) 2004 American Institute of Physics.

Changes in functional behavior of 93 % Pb(Mg1/3Nb2/3)O-3-7 % PbTiO3 thin films induced by ac electric fields

The dielectric properties of Au/[93%Pb(Mg1/3Nb2/3)O-3-7%PbTiO3] (PMN-PT)/(La0.5Sr0.5)CoO3/MgO thin-film capacitor heterostructures, made using pulsed laser deposition, have been investigated, with particular emphasis on the changes in response associated with increasing the magnitude of the ac measuring field. It was found that increasing the ac field caused a change in the frequency spectrum of relaxators, increasing the speed of response of "slow" relaxators, with an associated decrease in the freezing temperature (T-f) of the relaxor system; in addition, other characteristic parameters relating to polar relaxation (activation energy E-a and attempt frequency 1/tau(0)), described by fitting of the dielectric response to a Vogel-Fulcher expression, were found to change continuously as ac field levels were increased.

Fast-beam study of H2+ ions in an intense femtosecond laser field

A fast beam of H-2(+) ions, produced from a low energy ion accelerator, has been used for the first time in intense laser field experiments. The technique has enabled neutral dissociation products to be analysed and detected for the first time in such studies. Energy spectra of neutral and ionized fragments, product yields as a function of focused laser intensity and angular distributions of neutral dissociation products have been measured. Significant differences are observed between the present results and those obtained from experiments involving neutral H-2 molecules. These differences are indicative of the precursor H-2 molecule playing an important and hitherto neglected formative role in the laser-induced fragmentation processes.

Rotation of a nanoparticle cloud in an inductively coupled plasma induced by weak static magnetic fields

Hydrocarbon nanoparticles with diameters between 10 and 30 nanometres are created in a low pressure plasma combining capacitive and inductive power coupling. The particles are generated in the capacitive phase of the experiment and stay confined in the plasma in the inductive phase. The presence of these embedded particles induces a rotation of a particle-free region (void) around the symmetry axis of the reactor. The phenomenon is analysed using optical emission spectroscopy both line integrated and spatially resolved via an intensified charge coupled device camera. From these data, electron temperatures and densities are deduced. We find that the rotation of the void is driven by a tangential component of the ion drag force induced by an external static magnetic field. Two modes are observed: a fast rotation of the void in the direction opposite to that of the tangential component and a slow rotation in the same direction. The rotation speed decreases linearly with the size of the particles. In the fast mode the dependence on the applied magnetic field is weak and consequently the rotation speed can serve as a monitor to detect particle sizes in low temperature plasmas.

Recent advances in understanding CO oxidation on gold nanoparticles using density functional theory

Since the discovery of a series of Au-based catalysts by Haruta et al. considerable progress has been made in understanding the active role of Au in CO oxidation catalysis. This review provides a summary of recent theoretical work performed in this field; in particular it addresses DFT studies of CO oxidation catalysis over free and supported gold nanoparticles. Several properties of the Au particles have been found to contribute to their unique catalytic activity. Of these properties, the low-coordination state of the Au atoms is arguably the most pertinent, although other properties of the Au cluster atoms, such as electronic charge, cannot be ignored. The current consensuses regarding the mechanism for CO oxidation over Au-based catalysts is also discussed. Finally, water-enhanced catalysis of CO oxidation on Au clusters is summarized.

Identifying an O-2 supply pathway in CO oxidation on Au/TiO2(110): A density functional theory study on the intrinsic role of water

Au catalysis has been one of the hottest topics in chemistry in the last 10 years or so. How O-2 is supplied and what role water plays in CO oxidation are the two challenging issues in the field at the moment. In this study, using density functional theory we show that these two issues are in fact related to each other. The following observations are revealed: (i) water that can dissociate readily into OH groups can facilitate O-2 adsorption on TiO2; (ii) the effect of OH group on the O-2 adsorption is surprisingly long-ranged; and (iii) O-2 can also diffuse along the channel of Ti (5c) atoms on TiO2(1 10), and this may well be the rate-limiting step for the CO oxidation. We provide direct evidence that O-2 is supplied by O-2 adsorption on TiO2 in the presence of OH and can diffuse to the interface of Au/TiO2 to participate in CO oxidation. Furthermore, the physical origin of the water effects on Au catalysis has been identified by electronic structure analyses: There is a charge transfer from TiO2 in the presence of OH to O-2, and the O-2 adsorption energy depends linearly on the 02 charge. These results are of importance to understand water effects in general in heterogeneous catalysis.

Catalytic role of gold in gold-based catalysts: A density functional theory study on the CO oxidation on gold

Gold-based catalysts have been of intense interests in recent years, being regarded as a new generation of catalysts due to their unusually high catalytic performance. For example, CO oxidation on Au/TiO2 has been found to occur at a temperature as low as 200 K. Despite extensive studies in the field, the microscopic mechanism of CO oxidation on Au-based catalysts remains controversial. Aiming to provide insight into the catalytic roles of Au, we have performed extensive density functional theory calculations for the elementary steps in CO oxidation on Au surfaces. O atom adsorption, CO adsorption, O-2 dissociation, and CO oxidation on a series of Au surfaces, including flat surfaces, defects and small clusters, have been investigated in detail. Many transition states involved are located, and the lowest energy pathways are determined. We find the following: (i) the most stable site for O atom on Au is the bridge site of step edge, not a kink site; (ii) O-2 dissociation on Au (O-2-->20(ad)) is hindered by high barriers with the lowest barrier being 0.93 eV on a step edge; (iii) CO can react with atomic O with a substantially lower barrier, 0.25 eV, on Au steps where CO can adsorb; (iv) CO can react with molecular O-2 on Au steps with a low barrier of 0.46 eV, which features an unsymmetrical four-center intermediate state (O-O-CO); and (v) O-2 can adsorb on the interface of Au/TiO2 with a reasonable chemisorption energy. On the basis of our calculations, we suggest that (i) O-2 dissociation on Au surfaces including particles cannot occur at low temperatures; (ii) CO oxidation on Au/inactive-materials occurs on Au steps via a two-step mechanism: CO+O-2-->CO2+O, and CO+O-->CO2; and (iii) CO oxidation on Au/active-materials also follows the two-step mechanism with reactions occurring at the interface.

Bystander effects induced by diffusing mediators after photodynamic stress.

The bystander effect, whereby cells that are not traversed by ionizing radiation exhibit various responses when in proximity to irradiated cells, is well documented in the field of radiation biology, Here we demonstrate that considerable bystander responses are also observed after photodynamic stress using the membrane-localizing dye deuteroporphyrin (DP). Using cells of a WTK1 human lymphoblastoid cell line in suspension and a transwell insert system that precludes contact between targeted and bystander cells, we have shown that the bystander signaling is mediated by diffusing species. The extranuclear localization of the photosensitizer used suggests that primary DNA damage is not the trigger for initiating these bystander responses, which include elevated oxidative stress, DNA damage (micronucleus formation), mutagenesis and decreased clonogenic survival. In addition, oxidative stress in the bystander population was reduced by the presence of the membrane antioxidant vitamin E in the targeted cells, suggesting that lipid peroxidation may play a key role in mediating these bystander effects. The fluence responses for these bystander effects are non-linear, with larger effects seen at lower fluences and toxicity to the target cell population. Hence, when considering outcomes of photodynamic action in cells and tissue, bystander effects may be significant, especially at sublethal fluences.

Short pulse laser-induced dissociation of vibrationally cold, trapped molecular ions

An electrostatic trapping scheme for use in the study of light-induced dissociation of molecular ions is outlined. We present a detailed description of the electrostatic reflection storage device and specifically demonstrate its use in the preparation of a vibrationally cold ensemble of deuterium hydride (HD+) ions. By interacting an intense femtosecond laser with this target and detecting neutral fragmentation products, we are able to elucidate previously inaccessible dissociation dynamics for fundamental diatomics in intense laser fields. In this context, we present new results of intense field dissociation of HD+ which are interpreted in terms of recent theoretical calculations.

Role of creatine supplementation on exercise-induced cardiovascular function and oxidative stress

Many degenerative diseases are associated with increased oxidative stress. Creatine has the potential to act as an indirect and direct antioxidant; however, limited data exist to evaluate the antioxidant capabdities of creatine supplementation within in vivo human systems. This study aimed to investigate the effects of oral creatine supplementation on markers of oxidative stress and antioxidant defenses following exhaustive cycling exercise. Following preliminary testing and two additional familiarization sessions, 18 active males repeated two exhaustive incremental cycling trials (T1 and T2) separated by exactly 7 days. The subjects were assigned, in a double-blind manner, to receive either 20 g of creatine (Cr) or a placebo (P) for the 5 days preceding T2. Breath-by-breath respiratory data and heart rate were continually recorded throughout the exercise protocol and blood samples were obtained at rest (preexercise), at the end of exercise (postexercise), and the day following exercise (post24 h). Serum hypdroperoxide concentrations were elevated at postexercise by 17 +/- 5% above preexercise values (p = 0.030). However, supplementation did not influence lipid peroxidation (serum hypdroperoxide concentrations), resistance of low density lipoprotein to oxidative stress (t(1/2max) LDL oxidation) and plasma concentrations of non-enzymatic antioxidants (retinol, alpha-carotene, beta-carotene, alpha-tocopherol, gamma-tocopherol, lycopene and vitamin Q. Heart rate and oxygen uptake responses to exercise were not affected by supplementation. These findings suggest that short-term creatine supplementation does not enhance non-enzymatic antioxidant defence or protect against lipid peroxidation induced by exhaustive cycling in healthy males.

Generation of entangled coherent states via cross-phase-modulation in a double electromagnetically induced transparency regime

The generation of an entangled coherent state is one of the most important ingredients of quantum information processing using coherent states. Recently, numerous schemes to achieve this task have been proposed. In order to generate travelling-wave entangled coherent states, cross-phase-modulation, optimized by optical Kerr effect enhancement in a dense medium in an electromagnetically induced transparency (EIT) regime, seems to be very promising. In this scenario, we propose a fully quantized model of a double-EIT scheme recently proposed [D. Petrosyan and G. Kurizki, Phys. Rev. A 65, 33 833 (2002)]: the quantization step is performed adopting a fully Hamiltonian approach. This allows us to write effective equations of motion for two interacting quantum fields of light that show how the dynamics of one field depends on the photon-number operator of the other. The preparation of a Schrodinger cat state, which is a superposition of two distinct coherent states, is briefly exposed. This is based on nonlinear interaction via double EIT of two light fields (initially prepared in coherent states) and on a detection step performed using a 50:50 beam splitter and two photodetectors. In order to show the entanglement of an entangled coherent state, we suggest to measure the joint quadrature variance of the field. We show that the entangled coherent states satisfy the sufficient condition for entanglement based on quadrature variance measurement. We also show how robust our scheme is against a low detection efficiency of homodyne detectors.

Cold-Atom-Induced Control of an Optomechanical Device

We consider a cavity with a vibrating end mirror and coupled to a Bose-Einstein condensate. The cavity field mediates the interplay between mirror and collective oscillations of the atomic density. We study the implications of this dynamics and the possibility of an indirect diagnostic. Our predictions can be observed in a realistic setup that is central to the current quest for mesoscopic quantumness.

Retrodirective Array Performance in the Presence of Near Field Obstructions

We investigate the situation where there are obstructing elements present in the near field of a retrodirective array. We describe three scattering cases, (1) by an array of straight wires, (2) by low loss medium density fibre board partially obscuring the array, and (3) by concrete blocks, totally and then partially obscuring the array. For all scenarios retrodirective action was shown to be able to provide various degrees of automatic compensation for loss in gain relative to that which would have occurred for a conventional (non-retrodirective) array in the presence of the same scattering screens. Gain improvements of up to 10 dB were observed when the retrodirective array was used. In addition we show how the induced variation of received and re-transmited amplitudes across the array, caused by the scattering screens, is the principle mechanism causing deterioration of the retrodirective arrays monostatic response.