A semiclassical coupled-channels description of electron-molecule scattering is developed within the vibron model of diatomic molecules. The inclusive quasielastic scattering cross section is calculated for a typical system. The effect of the rotational coupling is taken into account by evaluating a rotationally inclusive cross section.

Positronium formation and target excitation in positron-helium scattering have been investigated using the close-coupling approximation with realistic wave functions for the positronium and helium atoms. The following eight states have been used in the close-coupling scheme: $\mathrm{He}\mathrm{}\left(1s1s\right),$ $\mathrm{He}{(1s2\mathrm{}}^{1}s),$ $\mathrm{He}{(1s2\mathrm{}}^{1}p),$ $\mathrm{He}{(1s3\mathrm{}}^{1}s),$ $\mathrm{He}{(1s3\mathrm{}}^{1}p),$ $\mathrm{Ps}\mathrm{}\left(1s\right),$ $\mathrm{Ps}\mathrm{}\left(2s\right),$ and $\mathrm{Ps}\mathrm{}\left(2p\right),$ where Ps stands for the positronium atom. Calculations are reported of differential cross sections for elastic scatering, inelastic target excitation to $\mathrm{He}{(1s2\mathrm{}}^{1}s)$ and $\mathrm{He}{(1s2\mathrm{}}^{1}p)$ states, and rearrangement transition to $\mathrm{Ps}\mathrm{}\left(1s\right),$ $\mathrm{Ps}\mathrm{}\left(2s\right),$ and $\mathrm{Ps}\mathrm{}\left(2p\right)\mathrm{}$ states for incident positron energies between 40 and 200 eV. The coincidence parameters for the transition to the $\mathrm{He}{(1s2\mathrm{}}^{1}p)$ state of helium are also reported and briefly discussed.

An extended version of the statistical energy-deposition model is used for a description of multiple ionization of molecules by energetic ion impact. The energy transferred to the molecule during the collision is calculated as a function of the impact parameter within the local-electron-density approximation for a fixed molecular orientation. The fluctuating character of the deposited energy is taken into account by introducing a straggling of the energy transfer. For a given deposited energy the probability of multiple ionization of the molecule is assumed to be proportional to the volume of phase space available at the considered ionization state. The total ionization cross section is obtained by integrating over impact parameters and averaging over all orientations of the molecule. Sample calculations for collisions of He and F ions with N${}_2$ and CO molecules are presented and compared with experimental data. A dependence of the multiple ionization cross section on the molecular orientation is considered. A strong molecule alignment effect has been obtained in agreement with recent experimental findings.

Based on the $R$-matrix method, photoionization cross sections of He below the $N=2\mathrm{}$ threshold of ${\mathrm{He}}^{+}$ are calculated, and a definite assignment of the doubly excited resonance states is determined by the eigenchannel treatment. Our results are in good agreement with the experimental data and other theoretical works. The polarization effects on the doubly excited states are studied in detail. We elucidate the effects of the dynamic polarization within the reaction zone (i.e., $R$-matrix box) and the long-range static polarization potentials outside the reaction zone, which influence the resonance energies and the profiles of He resonance states.

An uncoupled correlated variational method (i.e., explicitly using the interelectronic coordinates) for calculations involving several electrons is introduced. All the overlap and Hamiltonian matrix elements, including those involving the electron-electron interaction, are simple products of one-dimensional integrations. Although simple to implement, the method yields the best available energy for the ground state of the He zeroth-order Hamiltonian $H_0{=H}_1{+H}_2{+1/r}_{12}.$ Preliminary nonoptimized and nonextrapolated calculations yield $E=-2.9037243770341195938\left(50\right)\mathrm{}\mathrm{a}.\mathrm{u}.\mathrm{}$

The photoelectron imaging spectrometer has been used to investigate the resonant multiphoton ionization of xenon and hydrogen. Under certain conditions, extremely sharp unexpected features appear in the photoelectron images. It is shown that these features are produced by the residual ions acting as a microscopic lens that distorts the trajectories of the photoelectrons. The relevance of this phenomenon in zero electron kinetic energy spectroscopy and in experiments concerned with angular distribution measurements in strong-laser-field multiphoton ionization or in the photodetachment microscope is discussed.

The series of H${}^{-}$ resonances of ${}^1{P}^o$ symmetry predicted to converge exponentially to all thresholds has been investigated below the H$\mathrm{}(n=2\mathrm{})\mathrm{}$ threshold. It is shown that the series will be terminated already after the third resonance when the relativistic and radiative splitting of the H$\mathrm{}(n=2\mathrm{})\mathrm{}$ states is considered. Resonance parameters of this third resonance have been calculated with highly correlated wave functions. The resonance is predicted to be situated $19\mu$eV below H${(2p}_{1/2})$ with a width of $0.06\mu$eV. Accurate resonance parameters are also given for the first two resonances and the photoabsorption cross section is calculated for the threshold region.

The leading Lamb-shift terms are evaluated for the valence electrons of neutral alkali-metal and coinage metal atoms (groups 1 and 11, respectively). The vacuum polarization (VP) contribution is treated using the Uehling potential and the self-energy (SE) contribution using either a density-based ${\alpha }^3$ expression or the $E_{\mathrm{SE}}{/E}_{\mathrm{VP}}$ ratios by Johnson and Soff [At. Data Nucl. Data Tables 33, 405 (1985)]. Both Dirac-Fock and model-potential wave functions are tested. The result for the valence $\mathrm{ns}$ electron is a destabilization, rising at moderate $Z$ values (30–80) as $Z^2$ and more steeply at high $Z.\mathrm{}$ The $\left(n-1\right)d$ electrons suffer an indirect stabilization. The effects are opposite those of kinetic Dirac relativity and about 1–2% of them. They are roughly half of the valence Breit interaction and rise to about 0.5% of the ionization potential for $Z=111\mathrm{}–119.$

Recent high-energy $\mathrm{}(e,3e)\mathrm{}$ experiments indicate that the one-step mechanism (shake-off process) is insufficient. We have performed an ab initio calculation that takes into account all the two-step mechanisms of double ionization. This calculation uses the second Born approximation and correlated wave functions for the initial bound state. We show that the two-step processes are not negligible and must be added to the one-step process with the production of interference terms.

Dissociative electron attachment (DA) to single NO molecules and NO clusters is studied in two independent crossed electron–molecular-beam experiments with high-energy resolution including a kinetic-energy analysis of the ${\mathrm{O}}^{\mathrm{-}}$ fragment ions. It is shown that the DA cross section exhibits a vertical onset near 7.45 eV that corresponds to the energetic threshold of the DA channel ${\mathrm{O}}^{\mathrm{-}}{(}^{2}P)+{\mathrm{N}}^{*}{(}^{2}D).\mathrm{}$ No indication of the ground-state channel ${\mathrm{O}}^{\mathrm{-}}{(}^{2}P)+\mathrm{N}{(}^{4}S)$ [O. J. Orient and A. Chutjian, Phys. Rev. Lett. 74, 501 (1995)] and no indication of long-lived ${\mathrm{N}}^{\mathrm{-}}$ [H. Hiraoka, R. K. Nesbet, and L. W. Welsh, Jr., Phys. Rev. Lett. 29, 130 (1977)], as recently proposed, could be found. ${\mathrm{O}}^{\mathrm{-}}$ formation from NO clusters shows the same features as from single NO molecules, indicating the same reaction mechanism, thus also excluding coupling to the ground-state DA channel clusters.

A persistent problem in traditional high-field photoionization experiments is the intensity averaging caused by the use of focused laser beams. We show that it is possible to deconvolve ionization probabilities directly from data for experiments in which the detection volume is restricted. The inversion technique is outlined and as an example we apply it to multiphoton multiple-ionization measurements of xenon.

We demonstrate that weak magnetic fields can significantly enhance laser cooling and state preparation of Cs atoms in a one-dimensional optical lattice. A field parallel to the lattice axis increases the vibrational ground-state population of the stretched state $|m=F〉$ to $28\%$. A transverse field reduces the kinetic temperature. Quantum Monte Carlo simulations agree with the experiment, and predict $45\%$ ground-state population for optimal parallel and transverse fields. Our results show that coherent mixing and local energy relaxation play important roles in laser cooling of large-$F$ atoms.

We have measured and analyzed the clear emergence of ac-Stark-shifted multiphoton resonances with successive photon orders in xenon. The remarkable quality of our data illustrates the unambiguous evolution through parity-allowed resonances at the eight- and subsequent nine-photon levels. This marks a significant advance in showing that the transient resonance model is valid and strong optical-field ionization remains multiphoton in character at higher intensities. Furthermore, a simple Landau-Zener picture is sufficient to understand the basic principles.

We describe a method for measuring the density matrix of the transverse component of an atomic beam using a two-color, double-grating lateral shearing interferometer. From a set of measurements made in the far field of the atom interferometer, it is possible to reconstruct the one-particle density matrix with a very simple algorithm that involves no integral transforms.

Coherent states in the harmonic oscillator may be defined in several equivalent ways. One definition describes coherent states as special states satisfying a minimum-uncertainty requirement in position and momentum spaces. This definition is generalized for other potentials according to a method developed by Nieto et al. [Phys. Rev. D 20, 1321 (1979)] and is herein applied to the Pöschl-Teller potential. A classical limit based on the harmonic-oscillator coherent-state classical limit is then developed and applied to the Pöschl-Teller minimum-uncertainty states. In this limit, classical behavior may be obtained from these quantum states. Together with a completeness argument for the generalized coherent states, this result provides insight into quantum classical correspondence through the statistical interpretation of quantum mechanics.

An inequality is deduced from Einstein’s locality and a supplementary assumption. This inequality defines an experiment that can actually be performed with present technology to test local realism. Quantum mechanics violates this inequality a factor of 1.5. In contrast, quantum mechanics violates previous inequalities [for example, those of J. F. Clauser, M. A. Horne, A. Shimony, and R. A. Holt, Phys. Rev. Lett. 23, 880 (1969); S. J. Freedman and I. F. Clauser ibid. 28, 938 (1972); and J. F. Clauser and M. A. Horne, Phys. Rev. D 10, 526 (1974)] by a factor of $\sqrt{2}.$ Thus the magnitude of violation of the inequality derived in this paper is approximately 20.7% larger than the magnitude of violation of previous inequalities. This result can be particularly important for the experimental test of locality.

We propose an implementation of a universal set of one- and two-quantum-bit gates for quantum computation using the spin states of coupled single-electron quantum dots. Desired operations are effected by the gating of the tunneling barrier between neighboring dots. Several measures of the gate quality are computed within a recently derived spin master equation incorporating decoherence caused by a prototypical magnetic environment. Dot-array experiments that would provide an initial demonstration of the desired nonequilibrium spin dynamics are proposed.

In order to use quantum error-correcting codes to improve the performance of a quantum computer, it is necessary to be able to perform operations fault-tolerantly on encoded states. I present a theory of fault-tolerant operations on stabilizer codes based on symmetries of the code stabilizer. This allows a straightforward determination of which operations can be performed fault-tolerantly on a given code. I demonstrate that fault-tolerant universal computation is possible for any stabilizer code. I discuss a number of examples in more detail, including the five-quantum-bit code.

Approximate semianalytical solutions of the integral equation for the relativistic optimized potential are constructed by extending a method recently proposed by Krieger, Li, and Iafrate [Phys. Lett. A 146, 256 (1990)] to the relativistic regime. The quality of the approximation is tested in the longitudinal $x$-only limit where fully numerical solutions of the relativistic optimized effective potential integral equation are available for spherical atoms. The results obtained turn out to be in excellent agreement with the exact $x$-only values. The proposed method provides significant improvement over the conventional relativistic local density approximation and generalized gradient approximation schemes.

The ground-state hyperfine splitting values and the transition probabilities between the hyperfine structure components of high-$Z$ lithiumlike ions are calculated in the range $Z=49\mathrm{}$–83. The relativistic, nuclear, QED, and interelectronic interaction corrections are taken into account. It is found that the Bohr-Weisskopf effect can be eliminated in a combination of the hyperfine splitting values of the hydrogenlike and lithiumlike ions of an isotope. This gives a possibility for testing the QED effects in a combination of the strong electric and magnetic fields of the heavy nucleus. Using the experimental result for the $1s$ hyperfine splitting in ${}^{209}{\mathrm{Bi}}^{82+}$, the $2s$ hyperfine splitting in ${}^{209}{\mathrm{Bi}}^{80+}$ is calculated to be $\Delta E=0.7976\mathrm{}\left(2\right)\mathrm{}$ eV.