Improved Roothaan-Hartree-Fock wave functions are reported for the atoms from Cs through U. The largest improvement in the energy, relative to the wave functions of McLean and McLean [At. Data Nucl. Data Tables 26, 197 (1981)], is 0.065 hartree for Yb. The improved energies lie no more than 0.005 hartree above numerical Hartree-Fock limits.

Starting from a completely local relativistic density-functional theory, the total kinetic energy is first related to the virial plus contributions from the chemical potential of the electron cloud and classical potential-energy terms. Using the derivative of the Euler equation of the theory, the force term is then replaced in the virial by a function of the ground-state electron density. The theory is exemplified by two examples: (a) the relativistic Thomas-Fermi theory due to Vallarta and Rosen, and (b) heavy atoms in intense magnetic fields.

The ground-state energy of positronium negative ions, ${\mathrm{Ps}}^{\mathrm{-}}$, is calculated using double-basis-set Hylleraas functions in which four nonlinear parameters are used. The optimized result of E=-0.524 010 140 465 7 Ry obtained by using 744-term function represents the lowest variational energy for ${\mathrm{Ps}}^{\mathrm{-}}$ in the literature to date to our knowledge. The wave function is then used to calculate the positron annihilation rate for ${\mathrm{Ps}}^{\mathrm{-}}$.

A simple model employing the independent-electron approximation was developed to investigate orientation effects on the cross sections for multielectron ionization of diatomic molecules in fast-heavy-ion collisions. The model was used to compare K- and L-shell ionization cross sections for ${\mathrm{O}}_2$ molecules with internuclear axes oriented parallel and perpendicular to the beam.

The convergent close-coupling approach developed by the authors is applied to positron scattering from atomic hydrogen below the first excitation threshold. In this approach the multichannel-expansion one-electron states are obtained by diagonalizing the target Hamiltonian in a large Laguerre basis. It is demonstrated that this expansion of the scattering wave function is sufficient to reproduce the very accurate low-energy variational results, provided target states with l≤15 are included in the expansions.

We present a procedure for assessing changes in the order-1 Renyi entropy of the Bloch-vector trajectory of a two-level atom using only one Bloch-vector component. Entropy changes of the Bloch-vector trajectory are manifested in an alternate three-dimensional trajectory constructed from the time series of atomic-population variations using a simple delay-coordinate embedding procedure. This technique is shown to be robust in the presence of noise. Hence it provides a tool to aid in the experimental investigation of the correlations between Rabi resonances and entropy enhancements in atomic systems.

An interference experiment with signal photons from two parametric down-converters, based on the process of induced coherence without induced emission, has been performed. A low-Q optical cavity provides a possible time delay for the idlers. Whether the idler photon is to be delayed or not then determines whether the signal photon behaves like a wave and exhibits interference or behaves like a particle.

This Brief Report reports a study of coherent phenomena occurring in the collisional excitation of an atomic continuum of ionization structured by intense laser radiation. Two interfering pathways to the continuum, induced by interatomic interaction processes (collision-induced ionization and radiative-collisional excitation followed by photoionization), give rise to Fano-type line shapes for the cross section of the process.

In a recent paper Jamieson, Dalgarno, and Yukich [Phys. Rev. A 46, 6956 (1992)] discuss the elastic scattering of two hydrogen atoms at very low collision energies. They use as an input to their numerical calculations the potential-energy curve of the ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{u}}^{+}{}_{}{}^{}$ state obtained from a configuration-interaction (CI) calculation and report a triplet scattering length that is much larger than found previously. We show that the difference is a consequence of the neglect of a systematic shift in the b ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{u}}^{+}{}_{}{}^{}$ curve. Furthermore, we show that by taking the systematic shift into account, the scattering length of the CI potential reduces to a value of (1.2±0.2)${\mathit{a}}_0$, which is in agreement with previous results.

Photodissociation probabilities of rotationless ${\mathrm{H}}_2^{+}$ at λ=769 nm, from numerical solutions of the time-dependent Schrödinger equation, exhibit minima which are attributed to trapping in one- and three-photon field-induced potential wells, leading to molecular stabilization. Rotational excitations are shown to destroy the three-photon stabilization, whereas the one-photon trapping and stabilization of the bound molecular states at high intensities can persist in the presence of rotational excitation.

The vibrational dependence of dissociative attachment in low-energy ${\mathrm{Na}}_2$(v’’)+${\mathit{e}}^{\mathrm{-}}$ collisions (${\mathit{E}}_{\mathit{e}\mathit{l}}$<1.0 eV) is studied with a crossed-beam apparatus. The ${\mathrm{Na}}_2$ vibrational distribution is controlled through Franck-Condon pumping. A range of vibrational levels with energies up to approximately 60% of the molecular binding energy is covered. We observe a three orders of magnitude increase in the dissociative attachment rate for low lying and intermediate vibrational levels v’’. Further analysis shows a strikingly abrupt leveling off above v’’≊12.

High-resolution (width ∼0.12 eV) resonant Auger spectra of HBr and DBr after the Br 3d→${\mathrm{\sigma }}^{\mathrm{*}}$ transition are reported. Besides the atomic decay of ${\mathrm{Br}}^{\mathrm{*}}$(3${\mathit{d}}^9$4${\mathit{s}}^2$4${\mathit{p}}^6$) produced by dissociation of HBr after the antibonding transition, the molecular decay of ${\mathrm{HBr}}^{\mathrm{*}}$(3${\mathit{d}}^9$${\mathrm{\sigma }}^{\mathrm{*}1}$) is also observed in this high-resolution study. Competition between the atomic and molecular decay is influenced by varying the photon energy and by isotopic substitution.

We propose a beam splitter for atomic de Broglie waves combining atomic reflection from an evanescent laser wave with induced transitions between ground-state sublevels in a homogeneous magnetic field. An inelastic change of Zeeman energy during the reflection results in an angular separation of the outgoing partial beams. By choosing suitable relative phases between the polarization components of the evanescent wave, a two-channel beam splitter with an adjustable splitting ratio can be realized.

We have calculated the ionization yield for a hydrogen atom irradiated by a short (5-cycle) intense pulse, with the atom initially in the 1s or 2p (m≠0) state. We numerically solved the time-dependent Schrödinger equation, first making the dipole approximation, and then including the photon momentum. At sufficiently high intensities we find significant differences between making and not making the dipole approximation, suggesting that atomic stabilization may break down in superintense fields.

Effects of radiation transport in the interaction of a laser beam with sodium vapor in an argon atmosphere are reported. Investigations of the temporal and spatial evolution of ground-state orientation, which is produced by optical pumping with a circularly polarized near-resonant laser beam, reveal a strong deviation from the expected pure diffusive behavior. Transverse profiles are narrowed considerably with increasing sodium density as well as with increasing pump intensity. The temporal decay of orientation is also drastically altered. A simplified nonlinear and nonlocal theoretical model of radiation trapping gives excellent qualitative agreement with the observations and allows an intuitive interpretation.

We show that polarization-gradient cooling occurs in the Λ system, simultaneously with velocity-selective coherent population trapping (VSCPT). Starting with a Doppler temperature sample, this process precools atoms and contains them, to within twice the recoil velocity, a range efficiently capturable by VSCPT. For sodium, this cooling may enhance the rate of three-dimensional VSCPT by 200 times over the rate achievable from Doppler precooling alone. We estimate that in 8 msec, for example, the atoms would be cooled in three dimensions to one-fourth the recoil temperature.

The quantum measurement of trigonometric variables is revisted. We show that the probability distributions of the sine and cosine operators of Susskind and Glogower [Physics 1, 49 (1964)] suffer unphysical features for nonclassical states. We suggest that any measurement of a trigonometric variable needs necessarily a joint measurement of the two cosine-sine phase quadratures. In this way unphysical quantum statistics are avoided, and no violation of the trigonometric calculus occurs for expected values. We show that this trigonometric measurement can be defined in general terms in the framework of quantum estimation theory.