Absolute optical oscillator strength densities for the excitations of the electrons $4p,$ $4s,$ and $3d$ have been measured. Their absolute optical oscillator strengths have also been obtained. An enhancement above the $4p$ ionization threshold in the photoabsorption spectrum was assigned as a delayed maximum which arises from the photoionization process of $4\overrightarrow{p}\epsilon d$ according to present Dirac-Slater calculation. In the energy region of $4s$ autoionization, we have observed several features that are absent in previous fast-electron-impact work, but exist in optical measurements. We clarify this discrepancy here. Two Rydberg series of optically forbidden transitions, i.e., ${4s}^{-1}{ns(}^{1}S)$ $\mathrm{}(n=5,6,7\mathrm{})\mathrm{}$ and ${4s}^{-1}{nd(}^{1}D)$ $\mathrm{}(n=4,5,6,7\mathrm{})\mathrm{}$ have been observed when the spectrometer worked at conditions with larger momentum transfers, namely, $K^2=0.23\mathrm{}$ a.u. and 0.67 a.u. Furthermore, the absolute optical oscillator strengths for the $3d$ excitation have been obtained.

Calculations of rate constants for the process of dissociative attachment of low-energy electrons to hydrogen halides HCl, HBr, and HI and for the reverse process of associative detachment based on the nonlocal resonance model are reported. The calculated data are of importance for the modeling of plasma processes, environmental chemistry, etc. The calculated dissociative attachment rate constants are found to be in good agreement with existing experimental data. It is shown that at low temperatures the rate constants are very sensitive to small changes of the parameters of the nonlocal resonance model used for the calculation of the rate constants and represent a severe test of the theory. The isotopic effect and its dependence on the temperature is also discussed. The calculations of rate constants for the reverse process of associative detachment are also reported and discussed.

We present a theoretical study of electron collisions on SiH and SiF free radicals in the low- and intermediate-energy range. More specifically, calculated elastic differential, integral and momentum transfer cross sections as well as grand total (elastic and inelastic) and absorption cross sections are reported in the (1–500)-eV energy range. A complex optical potential is used to represent the electron-radical interaction while the Schwinger variational iterative method combined with the distorted-wave approximation is used to solve the scattering equations. Comparisons were made between the calculated cross sections for SiH and SiF as well as with the existing experimental and theoretical data for electron scattering by silane molecule. Some interesting aspects of this comparison are discussed here.

We demonstrate the transfer of orbital angular momentum from a light beam to a trapped low-index particle. The particle is trapped in a dark annular region of a high-order Bessel beam and rotates around the beam axis due to scattering from the helical wave fronts of the light beam. A general theoretical geometrical optics model is developed that, applied to our specific situation, corroborates tweezing and transfer of orbital angular momentum to the low-index particle. Good quantitative agreement between theory and experiment for particle rotation rates is observed.

We generalize the theory of electromagnetically induced transparency (EIT) and slow group velocity for the case of the homogeneous and inhomogeneous line broadening in both one- and two-photon transitions which unavoidably takes place in solid materials with a long-lived spin coherence. We identify regimes of EIT where the linewidth can be essentially reduced due to inhomogeneous broadening and, moreover, can be proportional to the amplitude of the driving field rather than the intensity. We suggest also a class of solid materials, namely, rare-earth ion doped semiconductors or dielectrics with electricdipole allowed transitions, that is very promising for realization and applications of EIT.

We measure the power spectral densities, at relaxation oscillation frequencies, of the individual longitudinal modes and the total intensity of a Nd-doped yttrium aluminum garnet laser at low pumping rate. We then test relationships between these quantities that are derived from the modal rate equations theory. The theoretical relations for the two mode case are confirmed by the experiment. However, in the three-mode regime, theory and experiments do not agree well.

An experimental scheme for preparing a polarization entangled W states from four photons emitted by parametric down-conversion is proposed. We consider two different configurations and a method of improving the yield by using single-photon sources. In the proposed scheme, one uses only linear optical elements and photon detectors, so that this scheme is feasible by current technologies.

In a previous paper [Bhatia and Temkin, Phys. Rev. A $64,$ 032709-1 (2001)], electron-hydrogen S-wave scattering phase shifts were calculated using the optical potential approach. This method is now extended to the singlet and triplet electron-${\mathrm{He}}^{+}$ scattering in the elastic region. Phase shifts are calculated using Hylleraas-type correlation functions with up to 95 terms. Results are rigorous lower bounds to the exact phase shifts.

We propose using eight lasers with appropriate orientations and conditions to generate stable trio coherent states of an ion in a three-dimensional isotropic trap. Seven lasers whose orientations are important should be detuned to the third lower sideband of the ion vibrational motion. The eighth laser whose direction is not important should be in resonance with the ionic transition.

We present here a theoretical analysis of the propagation of a sequence of ultrashort pulses in an optically dense medium. The interaction is resonant and treated in the weak-field regime. Dispersion is dominant and induces important reshaping effects. We show that these effects depend crucially on the relative phase shift φ between the pulses. Compared to the case of a train of independent pulses (i.e., mutually incoherent), a pulse sequence with $\phi =0\mathrm{}$ is shown to be sensitive to dispersion for lower optical depths, whereas a pulse sequence with $\phi =\pi$ is shown to be more robust.

A determination of the angular distribution parameter $\beta$ of the $3d$ and $4s$ main lines of atomic scandium in the resonance region of the $3\overrightarrow{p}nd,ms$ excitations has been carried out using electron spectrometry in conjunction with monochromatized synchrotron radiation. These measurements reveal strong variations of $\beta$ throughout the entire resonance region, highlighting the complicated nature of the ionization process for this first and seemingly simple $3d$ transition metal. The $\beta$ values of the photoelectrons resulting in $4s$ subshell ionization deviate significantly from 2.0 in qualitative, but not quantitative, agreement with recent many-body perturbation-theory calculations.

A relativistic version of the (consistent or decoherent) histories approach to quantum theory is developed on the basis of earlier work by Hartle, and used to discuss relativistic forms of the paradoxes of spherical wave packet collapse, Bohm’s formulation of the Einstein-Podolsky-Rosen paradox, and Hardy’s paradox. It is argued that wave function collapse is not needed for introducing probabilities into relativistic quantum mechanics, and in any case should never be thought of as a physical process. Alternative approaches to stochastic time dependence can be used to construct a physical picture of the measurement process that is less misleading than collapse models. In particular, one can employ a coarse-grained but fully quantum-mechanical description in which particles move along trajectories, with behavior under Lorentz transformations the same as in classical relativistic physics, and detectors are triggered by particles reaching them along such trajectories. States entangled between spacelike separate regions are also legitimate quantum descriptions, and can be consistently handled by the formalism presented here. The paradoxes in question arise because of using modes of reasoning which, while correct for classical physics, are inconsistent with the mathematical structure of quantum theory, and are resolved (or tamed) by using a proper quantum analysis. In particular, there is no need to invoke, nor any evidence for, mysterious long-range superluminal influences, and thus no incompatibility, at least from this source, between relativity theory and quantum mechanics.

The Casimir effect results from alterations of the zero-point electromagnetic energy introduced by boundary conditions. For ferromagnetic layers separated by vacuum (or a dielectric), such boundary conditions are influenced by the magneto-optical Kerr effect. We will show that this gives rise to a long-range magnetic interaction and discuss the effect for two different configurations (magnetization parallel and perpendicular to the layers). Analytical expressions are derived for two models and compared to numerical calculations. Numerical calculations of the effect for Fe are also presented and the possibility of an experimental observation of the Casimir magnetic interaction is discussed.

We have performed a proof-of-principle experiment in which qubits encoded in the polarization states of single photons from a parametric down-conversion source were coherently stored and read out from a quantum memory device. The memory device utilized a simple free-space storage loop, providing a cyclical readout that could be synchronized with the cycle time of a quantum computer. The coherence of the photonic qubits was maintained during switching operations by using a high-speed polarizing Sagnac interferometer switch.

A thorough numerical illustration of an optimal control scenario dealing with the laser-induced orientation of a diatomic molecule (LiF) is presented. Special emphasis is laid on the definition of the various targets dealing with different orientation characteristics, identified in terms of maximum efficiency (i.e., molecular axis direction closest to the direction of the laser polarization vector), maximum duration (i.e., the time interval during which this orientation is maintained), or of a compromise between efficiency and duration. Excellent postpulse orientation is achieved by sudden, intense pulses. Thermal effects are also studied with an extension of the control scenarios to Boltzmann averaged orientation dynamics at $T=5\mathrm{}\mathrm{K}.$

Motivated by a recent experiment [J. Eschner et al., Nature (London) 413, 495 (2001)], we now present a theoretical study on the fluorescence of an atom in front of a mirror. On the assumption that the presence of the distant mirror and a lens imposes boundary conditions on the electric field in a plane close to the atom, we derive the intensities of the emitted light as a function of an effective atom-mirror distance. The results obtained are in good agreement with the experimental findings.

The Grover quantum search algorithm is generalized to deal with an arbitrary mixed initial state. The probability to measure a marked state as a function of time is calculated, and found to depend strongly on the specific initial state. The form of the function, though, remains as it is in the case of initial pure state. We study the role of the von Neumann entropy of the initial state, and show that the entropy cannot be a measure for the usefulness of the algorithm. We give few examples and show that for some extremely mixed initial states (carrying high entropy), the generalized Grover algorithm is considerably faster than any classical algorithm.

We present an inequality that classifies mixed multipartite systems of an arbitrary dimension with respect to separability and positivity of partial transpose properties. This inequality gives a way to experimentally classify the observed state of multipartite systems of an arbitrary dimension. The inequality also implies that a sufficient condition for a density operator to have no positive partial transpose with respect to any subsystem is that the fidelity to a generalized Greenberger-Horne-Zeilinger state [A. Cabello, Phys. Rev. A 63, 022104 (2001)] is larger than 1/2 for mixed multipartite systems of an arbitrary dimension.

Theoretical models are constructed of the hard x-ray spectra resulting from electron capture by fully stripped ${\mathrm{Ne}}^{10+}$ ions traversing the gases Ne, He, ${\mathrm{H}}_2,$ ${\mathrm{CO}}_2,$ and ${\mathrm{H}}_2\mathrm{O}.$ The measured spectra are superpositions of individual lines of ${\mathrm{Ne}}^{9+}.$ An exact description of the radiative cascade is used. Initial excited populations that reproduce the measured spectra are derived and quantitative predictions of the energies and intensities of lines in the soft x-ray and extreme ultraviolet regions are made. These lines when observed will be powerful diagnostic probes of the capture mechanism and of the diverse range of laboratory and astrophysical plasmas in which it occurs.