Density-functional theory requires knowledge of the kinetic-energy density $t\left(\mathbf{r}\right)$ in terms of the ground-state density $\rho \left(\mathbf{r}\right).\mathrm{}$ Of course, the direct route to total kinetic energy is from the momentum density $n\left(\mathbf{p}\right),$ which in turn is directly related by Fourier transform to the first-order density matrix $\gamma (\mathbf{r},{\mathbf{r}}^{\prime }).\mathrm{}$ Here, an alternative route to calculate the total kinetic energy is explored, via the Fourier transform $ñ\left(\mathbf{r}\right)$ of the momentum density $n\left(\mathbf{p}\right).\mathrm{}$ It is shown that $ñ\left(\mathbf{r}\right)$ is related to the density matrix γ through its contracted form $\int \gamma ({\mathbf{r}}^{\prime }-\mathbf{r},{\mathbf{r}}^{\prime })d{\mathbf{r}}^{\prime }=ñ\left(\mathbf{r}\right).\mathrm{}$ As examples, bare Coulomb field and harmonic confinement for arbitrary numbers of closed shells are treated. Finally, a localized potential $V\left(\mathbf{r}\right)$ embedded in an initially uniform electron gas is considered, but now to low order in a perturbation series in $V\left(\mathbf{r}\right).\mathrm{}$

A model is proposed to study the inner-shell (K- shell) ionization of the inert gas atoms (e.g., Ne, Ar, etc.) by fast electron impact in coplanar geometry in the framework of a distorted wave approximation. An independent particle model is employed with a one-electron orbital for the multielectron target atom. Triple differential cross sections (TDCS) are presented for both symmetric and asymmetric kinematics of neon atom. The most salient feature noted in the TDCS structure is the presence of intense recoil peak that for certain dynamics (particularly when the ejected energy is much lower than the K-shell binding energy) is even larger than the binary peak, an unusual feature for the outer-shell ionization process. Results are compared with the relative measurements [P. Bickert and W. Hink, in 2nd European Conference on $\mathrm{}(e,2e)\mathrm{}$ Collisions and Related Problems (Kaiserslautern, 1989), edited by H. Ehrhardt] and the theoretical distorted-wave Born approximation results, available only for asymmetric kinematics. The qualitative agreement of the present results with the experiment by Bickert and Hink is quite good, particularly in respect to the binary/recoil intensity ratio, the latter being greater than unity in both cases for the particular dynamics at which the measurements by Bickert and Hink were performed. Additional results are also presented for symmetric as well as some other asymmetric kinematics.

We demonstrate the usefulness of the time-dependent coupled channel (TDCC) method in theoretical studies of atomic rearrangement collisions. In the TDCC method, coupled-channel partial differential equations for scattering wave functions are solved time dependently. We develop the Hankel-interpolation method, which is used to transform wave functions from an initial coordinate to a final coordinate system. By using this method, reaction cross sections of rearrangement collisions can be directly extracted from solutions of TDCC equations. We calculate positronium-formation cross sections in positron-hydrogen collisions in which a considerable number of theoretical calculations and precise experiments have been made. The present results for positron energies of 6.8–35 eV are in excellent agreement with the recent experiment of Zhou et al. [Phys. Rev. A 55, 361 (1997)].

We prove that for a symmetric complex potential, the probabilities of quantal reflection and transmission of a particle are independent of the direction of incidence of the particle. However, the reflectivity for a nonsymmetric complex potential is found to be sensitive to the direction of incidence of the particle whether it is incident from left or right.

We have used the one-center close coupling method to calculate the electron detachment cross sections of the hydrogen negative ion by antiproton impact. The one- and two-electron treatments give similar cross sections for single detachment. The double-detachment cross section is estimated within an independent particle model, and is at most a few percent of the single-detachment cross section. The single-ionization cross sections of helium in antiproton impact are recalculated including the double-ionization channels which were completely neglected in our previous calculation [Phys. Rev. A $62,$ 052722 (2000)]. However, the inclusion of the double-ionization channels does not make a great difference for the single-ionization cross sections above 1 keV and disagreement still remains with the data measured by Hvelplund et al. [J. Phys. B $27,$ 925 (1994)].

Transmission of highly charged ions through microcapillaries is studied theoretically by a classical trajectory simulation. The interaction of highly charged ions with the internal surface of the capillary is treated within the framework of dielectric-response theory. The simulation is based on the classical over-the-barrier model modified for open cylindrical surfaces. The multielectron evolution and relaxation is taken into account as a stochastic event sequence. We consider ${\mathrm{N}}^{6+}$ and ${\mathrm{Ne}}^{10+}$ with an energy of 2.1 keV/amu passing through a metallic microcapillary of Ni. We analyze the distance of closest approach, the angular distribution, and the distribution of the mean occupation numbers of n shells of highly charged ions. We find the resulting charge state distribution of transmitted projectiles in good agreement with recent measurements. Implications for nanotube targets will be discussed.

This paper seeks to address the problem of collisional energy transfer between atoms or molecules arranged in connecting layers on a solid surface in response to impulsive photon impact. An analysis based on classical trajectories of the motions of a line of touching spheres subject to impact at one end, computed by Green’s method, is adopted to describe the collisional behavior of atoms or molecules attached to a metal subsequent to electronic excitation by an ultrafast laser pulse. To highlight the essential dynamics, the characteristic line dissociation and rebound behavior of a series of connected spheres is investigated for different impact durations, amplitudes, and numbers of particles. The individual particle trajectories reveal the propagation of a disturbance along the line which results in fragmentation of the outermost particles from the remainder. In applying this scheme to energy transfer between molecules stacked on a low-temperature metal, a model of photon-induced, resonant electron scattering between displaced harmonic oscillators is invoked to estimate the magnitude of the impulsive force that acts on the atoms or molecules immediately adjacent to the solid surface. From the time-dependent line fragmentation velocities, kinetic energy distributions are calculated for photodesorption of benzene molecules from $\mathrm{Pt}\{111\}$ by a normally incident laser beam, and are compared with recent experimental measurements.

We have demonstrated that Raman transitions between adjacent momentum states of ground-state atoms can be used for velocimetry. We report measurements of the transverse velocity distribution of atoms in a beam with a thermal longitudinal velocity. The atomic density was 100 times lower than atoms released from a magneto-optical trap, and the resolution was a few recoils, under conditions where the usual geometric measurement would have been 100 times worse.

In this paper we report on the first purely “pump-probe” nonlinear laser spectroscopy results in a slow atomic beam. We have observed Raman, Rayleigh, and recoil-induced resonances (RIR) in a continuous beam of slow and cold cesium atoms extracted from a two-dimensional (2D) magneto-optical-trap (MOT) with the moving molasses technique. The RIR enabled us to measure the velocity distribution, therefore the average speed (0.6–4 m/s) and temperature (50–500 μK) of the atomic beam. Compared to time of flight, this technique has the advantage of being local, more sensitive in the low-velocity regime $(v<\mathrm{}1\mathrm{}\hspace{0.5em}\mathrm{m}/\mathrm{s}),$ and it gives access to transverse velocities and temperatures. Moreover, it may be extended to measure atomic velocities in the 2D MOT source of the atomic beam.

We present experiments of a laser with variable pulse energy and beam width saturating sodium vapor near the $D_1$-line transition. At high optical depth and in a buffer gas atmosphere of argon, the effect of nonlinear radiation trapping is shown to drastically change the spatial distribution and temporal evolution of the excited-state population and of the fluorescence light trapped by the nonlinear medium. Besides observing the transient behavior of the fluorescence light, a pump-probe beam experiment enables us to gain a tomographic view inside the atomic vapor. Nitrogen as a buffer gas is used to compare with the situation where radiation trapping effects are negligible. Finally, numerical simulations based upon equations of radiative transfer for a two-level atomic system elucidate the role of nonlinear radiation trapping and support given interpretations of the experiments.

Based upon our previous works [Eur. Phys. J. D 6, 319 (1999); Chin. Phys. Lett. 18, 236 (2001)], we develop a classical approach to calculate the high-order harmonic generation of the laser-driven atoms and molecules. The Coulomb singularities in the system have been removed by a regularization procedure. Action-angle variables have been used to generate the initial microcanonical distribution that satisfies the inversion symmetry of the system. The numerical simulation show, with a moderate laser intensity, a harmonic plateau with only odd harmonics appears. At higher intensities, the spectra become noisier because of the existence of chaos. With further increase in laser intensity, ionization takes place, and the high-order harmonics disappear. Thus, chaos introduces noise in the spectra, and ionization suppresses the harmonic generation, with the onset of the ionization follows the onset of chaos.

Within a mean field plus random-phase approximation formalism, we investigate the collective excitations of a three-component Fermi-Bose mixture of K atoms, magnetically trapped and subjected to repulsive s-wave interactions. We analyze both the single-particle excitation and the density oscillation spectra created by external multipolar fields for varying fermion concentrations. The formalism and the numerical output are consistent with the generalized Kohn theorem for the whole multispecies system. The calculations give rise to fragmented density excitation spectra of the fermion sample and illustrate the role of the mutual interaction in the observed deviations of the bosonic spectra with respect to Stringari’s rule.

Phase separation of a Bose-Fermi gas mixture in a trapping potential is strongly influenced by the interaction between the fermion and the boson. The stability condition for the mixture at zero temperature is deduced. It is found that mixture stability depends on the fermion-boson interaction, the total number of the bosons and the fermions, and the trapping frequencies. The stability conditions for the mixture at finite temperature are also derived and discussed.

The dielectronic recombination spectrum of ${\mathrm{N}}^{4+}$ has been measured with high resolution and accuracy. The ${1s}^{2}2p5l$ resonances in the energy range $0–1.6\mathrm{eV}$ were studied in detail. The experimental spectrum is compared with the results from four different calculations. An almost perfect agreement between the experiment and a calculation which combines relativistic many-body perturbation theory and complex rotation is found. The calculation provides accurate spectroscopic data for all fifty ${1s}^{2}2p5l$ states. The literature value for the ${1s}^{2}2p5s$ ${}^{1}P$ energy level is found to be off by more than 0.1 eV.

Electromagnetically induced transparency may lead to suppression of two-photon absorption in a four-level atomic system. This phenomenon is manifested by destructive quantum interference among multiple excitation paths created by a coherent coupling field. We report an experimental observation of such suppression of two-photon absorption in cold ${}^{87}\mathrm{Rb}$ atoms.

We present a detailed study of the interaction of ultrashort laser pulses with a resonant three level system (fine structure levels of rubidium). As expected, for low intensities a linear model and for higher intensities a semiclassical model (Maxwell-Bloch) is fully sufficient to describe the observed results. In both cases, however, it is essential to have an accurate knowledge of the incident electric field, i.e., the amplitude and the phase, in order to simulate the interaction process. It is shown that on small time scales the phase modulation of the incident pulse influences the reshaping process during pulse propagation whereas on longer time scales the reshaping is solely governed by the dynamics of the atomic system.

We show that there is no need for adiabatic passage in the storage and retrieval of information in the optically thick vapor of Lambda-type atoms. This information can be mapped into and retrieved out of long-lived atomic coherence with nearly perfect efficiency by strong writing and reading pulses with steep rising and falling edges. We elucidate similarities and differences between the “adiabatic” and “instant” light storage techniques, and conclude that for any switching time, an almost perfect information storage is possible if the group velocity of the signal pulse is much less than the speed of light in the vacuum c and the bandwidth of the signal pulse is much less then the width of the two-photon resonance. The maximum loss of the information appears in the case of instantaneous switching of the writing and reading fields compared with adiabatic switching, and is determined by the ratio of the initial group velocity of the signal pulse in the medium and speed of light in the vacuum c, which can be very small. Quantum restrictions to the storage efficiency are also discussed.

It is shown that the information losses due to the limited fidelity of continuous variable quantum teleportation are equivalent to the losses induced by a beam splitter of appropriate reflectivity.

We propose a scheme to accumulate fermionic or bosonic NH radicals ${(}^{14}\mathrm{NH}$ or ${}^{15}\mathrm{NH},$ respectively) in a magnetic trap in order to increase phase-space density. NH molecules prepared in a long-lived metastable state that exhibits a large Stark effect can be brought to a standstill using Stark deceleration. By applying an intense laser field, the NH radicals can then be forced to spontaneously decay to the electronic ground state. In the ground state the NH molecules are no longer sensitive to electric fields but show a significant Zeeman effect instead, enabling confinement and reloading of ground-state molecules in a magnetic trap.

An atom interferometer, whose arms are in the different sublevels, was demonstrated using two ${\sigma }^{+}$- and two ${\sigma }^{-}$-polarized, copropagating, laser beams in a magnetic field. Using the interferometer, Ramsey fringes with a width of 50 kHz were observed as a function of Zeeman shift frequency. The visibility of the interference fringes of 0.046 was obtained at an excitation power of almost $\pi /2\mathrm{}$ pulse area.