The direct differential cross section and the total cross section for scattering of 0.5-, 1.5-, and 5.0-keV ${\mathrm{H}}^{+},$ H, and He projectiles by He and Ne targets over the laboratory scattering angle range $0.01°-10.0°$ are studied using the electron nuclear dynamics theory, which treats the simultaneous dynamics of all electrons and nuclei. Emphasis is put on the quantum effects of the forward peak scattering. Comparison of the present results with available experimental data shows very good agreement.

Multiple-vacancy states for outer-shell electrons created in heavy-ion–atom collision have been studied through high-resolution measurement of the $L\gamma$ x rays emitted from ${}_{65}\mathrm{Tb}$ induced by 15- and 30-MeV carbon ions. For the $L{\gamma }_1$ x-ray emission, it is found that the satellite structure due to N-shell multiple vacancies can be well resolved from the satellite structures due to M-shell multiple vacancies. The spectral features observed provide experimental evidence for the manifestation of the exchange interaction between the ${4d}_{3/2}$ hole and the unpaired $4f$ electrons in the presence of several N vacancies. An interpretation of the observed satellite structure for the complex $L{\gamma }_{2,3}$ x-ray emission is presented.

The electronic stopping power of a material for swift molecules or clusters need not be an incoherent superposition of the stopping powers for the constituent atomic ions. However, only the stopping of hydrogen clusters is understood theoretically. Experimental results indicate that effects due to coherent stopping are smaller for heavier molecules and clusters, and occasionally destructive interferences were found experimentally when constructive interferences were expected. The present theoretical study aims at differences between the stopping of hydrogen and heavier clusters. The role of projectile screening is emphasized, and explicit estimates are presented for coherent-stopping effects due to target excitation or ionization. The importance of a proper description of target resonances is pointed out. As expected, projectile screening reduces the significance of coherent stopping. Competing effects such as projectile excitation or ionization, variations in charge-state and charge-dependent stopping, and the clearing-the-way effect are discussed qualitatively. The main focus is on randomly oriented beams, but attention is also given to stopping of aligned molecules.

We calculate the two-photon ionization of clusters for photon energies near the surface plasmon resonance. The plasmon is described in a schematic jellium-RPA model assuming a separable residual interaction between electrons determined so that the plasmon energy is reproduced. The ionization rate of a double plasmon excitation is calculated perturbatively. In ${\mathrm{Na}}_{93}^{+}$ clusters we find an ionization rate of the order of at most $0.05–0.10\hspace{0.5em}{\mathrm{fs}}^{-1}.$ This rate is used to determine the ionization probability in an external field in terms of the number of absorbed photon pairs and the duration of the field. We discuss the dependence of the results on the choice of our empirical separable force. The number of emitted electrons per pair of absorbed photons is found to be small, in the range ${10}^{-5}$ to ${10}^{-3}.$

In the presence of an intensive laser field the radiative recombination of the continuum electron into an atomic bound state generally is accompanied by absorption or emission of several laser quanta. The spectrum of emitted photons represents an equidistant pattern with the spacing equal to the laser frequency. The distribution of intensities in this spectrum is studied employing the Keldysh-type approximation, i.e., neglecting interaction of the impact electron with the atomic core in the initial continuum state. Within the adiabatic approximation the scale of emitted photon frequencies is subdivided into classically allowed and classically forbidden domains. The highest intensities correspond to emission frequencies close to the edges of classically allowed domain. The total cross section of electron recombination summed over all emitted photon channels exhibits negligible dependence on the laser field intensity.

Two internal hyperfine states of a Bose-Einstein condensate in a dilute magnetically trapped gas of ${}^{87}\mathrm{Rb}$ atoms are strongly coupled by an external field that drives Rabi oscillations between the internal states. Due to their different magnetic moments and the force of gravity, the trapping potentials for the two states are offset along the vertical axis, so that the dynamics of the internal and external degrees of freedom are inseparable. The rapid cycling between internal atomic states in the displaced traps results in an adiabatic transfer of population from the condensate ground state to its first antisymmetric topological state. This has a pronounced effect on the internal Rabi oscillations, modulating the fringe visibility in a manner reminiscent of collapses and revivals. We present a detailed theoretical description based on zero-temperature mean-field theory.

Exact solutions to many-body interacting systems of both bosonic and fermionic particles confined to harmonic potential in an arbitrary number of dimensions are given. Energy levels and their degeneracies for trapped identical particles interacting via harmonic forces are calculated. This specific form of the interaction allows for analytical solutions. The mutual interaction, attractive or repulsive, modifies significantly the properties of the considered system. For a large number of particles the interaction essentially results in a frequency shift. Statistical properties (e.g., microcanonical and grand canonical partition functions) as well as some illustrative, physically relevant examples are discussed. Our results give an unusual opportunity for further studies of interacting systems in the framework of the exactly soluble model.

We study the dynamics of a collection of two-level atoms interacting with a single mode of a quantized field in a dissipative cavity in the dispersive regime. The quantized mode is driven by a classical driving field. The steady-state density matrix is obtained. The influence of the driving field on the quantized driven field and on atomic properties in both the dissipative and the lossless cases is studied. The atomic decoherence time in the dissipative-driven case is obtained. We show that the external driving field strongly suppresses the atomic coherence (in comparison with the dissipative cavity without the driving field).

The continuous transition from a low resolution quantum nondemolition measurement of light field intensity to a precise measurement of photon number is described using a generalized measurement postulate. In the intermediate regime, quantization appears as a weak modulation of measurement probability. In this regime, the measurement result is strongly correlated with the amount of phase decoherence introduced by the measurement interaction. In particular, the accidental observation of half integer photon numbers preserves phase coherence in the light field, while the accidental observation of quantized values increases decoherence. The quantum mechanical nature of this correlation is discussed and the implications for the general interpretation of quantization are considered.

Starting from local universal isotropic disentanglement, a threshold inequality for reduction factors is proposed, which is necessary and sufficient for this type of disentanglement processes. Furthermore, we give the conditions realizing ideal disentanglement processes provided that some information on quantum states is known. In addition, based on a fully entangled fraction, a concept called inseparability correlation is presented. Some properties on inseparability correlation coefficient are studied.

Although there is no relative motion among different points on a rotating disk, each point belongs to a different noninertial frame. This fact, not recognized in previous approaches to the Ehrenfest paradox and related problems, is exploited to give a correct treatment of a rotating ring and a rotating disk. Tensile stresses are recovered, but, contrary to the prediction of the standard approach, it is found that an observer on the rim of the disk will see equal lengths of other differently moving objects as an inertial observer whose instantaneous position and velocity are equal to that of the observer on the rim. The rate of clocks at various positions, as seen by various observers, is also discussed. Some results are generalized for observers arbitrarily moving in flat or curved spacetime. The generally accepted formula for the space line element in a non-time-orthogonal frame is found inappropriate in some cases. The use of Fermi coordinates leads to the result that for any observer the velocity of light is isotropic and is equal to c, providing that it is measured by propagating a light beam in a small neighborhood of the observer.

Coupling nanocrystals (quantum dots) to a high-$Q$ whispering gallery mode (WGM) of a silica microsphere, can produce a strong coherent interaction between the WGM and the electronic states of the dots. Shifting the resonance frequencies of the dots, for instance by placing the entire system in an electric potential, then allows this interaction to be controlled, permitting entangling interactions between different dots in a way analogous to the ion-trap computer of Cirac and Zoller. Thus, a more advanced system of this type could potentially be used to implement a simple quantum computer.

The harmonic inversion method is applied in the case of the hydrogen atom in a magnetic field to extract classical information from the quantum photo-ionization cross section. The study is made close to a saddle-node bifurcation for which the usual semiclassical formulas give diverging contributions. All quantities (actions, stabilities, and Maslov indices) for real orbits above the bifurcation and for complex ghost orbits below the bifurcation, are found to be in excellent agreement with the modified semiclassical predictions based on a normal form approach.

It is shown that a specific beyond-dipole-approximation polarization effect in elastic photon-atom scattering, resulting in circular dichroism when the scattered photon has a suitable observed linear polarization, has significance in the x-ray regime. Ground-state atoms are considered, assumed to be randomly oriented. The cross section, given our assumptions, is written in terms of photon Stokes parameters and four real photon-polarization-independent atomic parameters (which depend on the vectors of the problem and the two invariant scattering amplitudes). Numerical results are given for the case of scattering from ground-state atoms with $Z=29,$ $Z=54,$ and $Z=92.\mathrm{}$ Attention is given to determining the regime where the dichroism effect may be experimentally observable. An ideal experiment would involve measuring the difference between the cross sections for right-handed and left-handed circularly polarized incident photons, observing a fixed linear polarization for the scattered photon which makes an angle of $45°$ with respect to the scattering plane. The effect is seen to be largest for intermediate angles, high Z and high (hundreds of keV) photon energies, increasing to an approximately 20% effect in cross sections. The parameter determining this effect is also responsible for the appearance of elliptically polarized scattered photons for the case of a suitable linearly polarized incident beam.

Fully relativistic, self-consistent field calculations, based on the Dirac-Coulomb-Gaunt Hamiltonian, were performed on the ground state of HBr, the $\mathrm{Br}3d$–ionized ${\mathrm{HBr}}^{+},$ and the 4$p(\pi ,\sigma {)}^{-2}$ states of ${\mathrm{HBr}}^{2+}.$ Correlation in the ground and valence-excited states and partially in the $\mathrm{Br}3d$ ionized states was described using a configuration-interaction (CI) method. Calculated ionization energies and bond lengths were found to be in good agreement with recent experimental results. The distortion in the vibrational bands of the ${3d}^{-1}\to 4p{\pi }^{-2}$ Auger transitions due to lifetime vibrational interference was verified through ab initio calculations. Bands due to the transitions to bound and continuum vibrational states of the same electronic state were reproduced by calculations and compared with experimentally determined profiles. The nonadiabatic effects in the spin-orbit-induced avoided level crossing were investigated using adiabatic and diabatic electronic basis sets.

Differential, integrated elastic, momentum transfer, total cross sections, and spin polarization parameters S, T, and U for scattering of electrons from Yb, Rn, and Ra atoms in energy range of 2.0–500.0 eV are calculated using the relativistic Dirac equation. The projectile-target interaction is represented both by real- and complex-optical potential in the solution of Dirac equation for the scattered electrons. The real-optical potential includes the static, a parameter-free correlation polarization potential and modified semiclassical exchange potentials. The complex potential is included via a phenomenological absorption potential to account for the loss of flux into the nonelastic channels. We compare our results for differential cross sections and spin polarization parameters with the available calculations and experimental measurements.

We report on a method to measure charge-changing cross sections for ions passing through matter in nonequilibrium conditions. The charge states of an initial distribution are separated by applying a high voltage before they penetrate thin carbon foils; the charge states after those foils are identified using a high resolution magnetic spectrometer. Thus the full matrix of cross sections $\sigma {(q}_i{,q}_f)$ and energy losses $\Delta {E(q}_i{,q}_f)$ is obtained. The data are compared to calculated charge-state distributions based on microscopic cross sections for charge-changing processes in individual interaction steps and with a Monte Carlo simulation.

Electron energy distributions arising from 2–6-keV protons grazingly incident on an Al(111) surface are reported for two different azimuthal angles of incidence and for a range of observation angles. Although the protons have energies that are an order of magnitude below the generally accepted threshold for plasmon excitation, the spectra strongly suggest that excitation and subsequent decay of bulk plasmons takes place. To explain this remarkable observation we propose that a subthreshold proton may excite a bulk plasmon in a process in which not only energy and momentum are transferred to the plasmon but also, mainly momentum, to the target.

Both quantal and semiclassical mean-field theories based on the density-functional theory have recently been applied to describe the dynamical evolution of electrons during and after the collision between highly charged ions and metallic clusters. We here compare and assess both methods. The quantal calculation solves the time-dependent Kohn-Sham equations, whereas the semiclassical one solves the Vlasov equation with the same exchange-correlation functional. Predicted observables such as electron transfer and residual electronic excitations are in excellent agreement with each other. Ranges of applicability of both methods are discussed and complementarities are emphasized.

We study spontaneous emission of electromagnetic radiation by an electron with given initial asymptotic momentum in interaction with a Coulomb field and with a homogeneous monochromatic electric field (laser field in dipole approximation). The intense field effects are taken into consideration for the initial and final continuum electron states, by using improved Volkov-Coulomb wave functions, including second-order corrections in the interaction with the electromagnetic field. For the evaluation of the transition amplitudes, the so-called three-$\delta$ approximation introduced by Korol [A. V. Korol, J. Phys. B 28, 3873 (1995)] is adopted. The numerical results are presented for a linearly polarized field of frequency of 0.117 eV, intensities up to ${10}^{-6}$ a.u., electron energies in the range 50–500 eV, and incident momentum orthogonal to the laser polarization direction. The study focuses on spontaneous emission accompanied by exchange of a fixed number $n=0,\pm 1,\pm 2$ of photons with the external field. Deviations from Born results are shown in several cases. We illustrate in graphs how the spontaneous emission is drastically reduced by the presence of the external field.