Using the dark-spot Zeeman-tuned slowing technique, we have measured the capture velocity of a magneto-optical trap as a function of the trap laser intensity. The values obtained are in reasonable agreement with calculations based on a simple model. Nevertheless, the dependence of capture velocity in the low-intensity regime seems to be slightly different from the predictions. The measurement of this type of trap parameter is of interest in the analysis of exoergic cold collisions, where the knowledge of such values is important for the interpretation of experimental results.

We propose a scheme for the creation of skyrmions (coreless vortices) in a Bose-Einstein condensate with hyperfine spin $F=1.\mathrm{}$ In this scheme, four traveling-wave laser beams, with Gaussian or Laguerre-Gaussian transverse profiles, induce Raman transitions with an anomalous dependence on the laser polarization, thereby generating the optical potential required for producing skyrmions.

We present a theory to derive the output rate of an atom laser consisting of an interacting Bose-Einstein condensate in a magnetic trap and two additional rf fields transferring trapped atoms to a repelled Zeeman sublevel via an intermediate untrapped Zeeman sublevel. We explicitly obtain the dependence of the output rate ${\Gamma }_{\mathrm{out}}$ on various characteristic parameters such as a coupling parameter (the Rabi frequency), the atom number density in the center of the condensate, and the strength of the atom-atom interaction.

The temporal evolution of an atomic wave packet interacting with object and reference electromagnetic waves is investigated beyond the weak perturbation of the initial state. It is shown that the diffraction of an ultracold atomic beam by the inhomogeneous laser field can be interpreted as if the beam passes through a three-dimensional hologram, whose thickness is proportional to the interaction time. It is found that the diffraction efficiency of such a hologram may reach 100% and is determined by the duration of laser pulses. On this basis a method for reconstruction of the object image with matter waves is offered.

The distortion of a spontaneous down-conversion process caused by an auxiliary mode coupled to the idler wave is analyzed. In general, a strong coupling with the auxiliary mode tends to hinder the down-conversion in a nonlinear medium. On the other hand, provided that the evolution is disturbed by the presence of a phase mismatch, the coupling may increase the speed of down-conversion. These effects are interpreted as being manifestations of quantum Zeno and anti-Zeno effects, respectively, and they are understood by using the dressed mode picture of the device. The possibility of using the coupling as a nontrivial phase-matching technique is pointed out.

An ensemble of spin-$\frac{1}{2}$ particles is observed repeatedly using Stern-Gerlach devices with varying orientations. Synthesis of such noncommuting observables is analyzed using the maximum likelihood estimation as an example of quantum-state reconstruction. Repeated incompatible observations represents a new generalized measurement. This idealized scheme will serve for analysis of future experiments in neutron and quantum optics.

We discuss long-range corrections for the integral boundary condition (IBC) introduced in A. M. Ermolaev, I. V. Puzynin, A. V. Selin, and S. I. Vinitsky, Phys. Rev. A 60, 4831 (1999), in the case of the time-dependent Schrödinger equation with a long-range atomic potential. As in the work of Ermolaev et al. the laser-atom interaction is taken in the dipole approximation. The IBC techniques require the knowledge of the Green’s function of the problem, beyond some surface $\sigma$ remote from the atom. We consider the eikonal approximation (EA) for the Green’s function in the asymptotic region and perform numerical tests on a one-dimensional problem with the soft Coulomb potential. We demonstrate that the account of long-range corrections, within the EA, allows us to reduce significantly the size of the space domain required for numerical integration and improves essentially on the accuracy of the computed spectral distribution for the ejected electrons.

The effect of spatial symmetry on strong-field ionization is investigated with one-dimensional two-electron ab initio quantum-mechanical calculations. Numerical results clearly show that the nonsequential double-ionization rate in atoms with spatially symmetric wave functions is higher than in atoms with antisymmetric wave functions. Moreover, single ionization is demonstrated to be correlated with double ionization, indicating that strong-field ionization is in fact a highly dynamic process.

We identify the physical origin of the loss of interference pattern in the which-path atom-interferometery experiments that have been discussed widely. The origin of complementarity between the which-path information and the interference pattern is a discrete spinor phase with random sign. This clarifies how complementarity can arise without the Heisenberg back action in momentum.

Spatial entanglements of macroscopic quantum systems are proposed. The which-path uncertainty of a single photon passing through a beam splitter is transformed into the which-path uncertainty of two macroscopic fields via two quantum nondemolition measurements. The macroscopic fields are nonlocally correlated.

In a series of interesting papers Hegerfeldt has shown that quantum systems with positive energy initially localized in a finite region immediately develop infinite tails. In our paper Hegerfeldt’s theorem is analyzed using quantum and classical wave packets. We show that Hegerfeldt’s conclusion remains valid in classical physics. No violation of Einstein’s causality is ever involved. Using only positive frequencies, complex wave packets are constructed which at $t=0\mathrm{}$ are real and finitely localized and which, furthermore, are superpositions of two nonlocal wave packets. The nonlocality is initially cancelled by destructive interference. However, this cancellation becomes incomplete at arbitrary times immediately afterwards. In agreement with relativity the two nonlocal wave packets move with the velocity of light, in opposite directions.

Based on local unitary operators acting on n-dimensional Hilbert spaces, we investigate selective and collective operator basis sets for N-particle quantum networks. Selective cluster operators are used to derive the properties of maximum entangled states (Bell states) for any n and N. Collective operators are convenient to account for fundamental or operational indistinguishability. For permutation symmetry the respective Hilbert-space dimension is only polynomial in N, and is governed by strong selection rules. These selection rules can be exploited for the design of decoherence-free subspaces as well as for the implementation of efficient routes to entanglement if suspended switching between states of different symmetry classes could be realized.

The radiative lifetime of the ${}^1{S}_0$ metastable state of ${\mathrm{Xe}}^{2+}$ has been measured with a different type of electrostatic ion trap. The ion trap stores ion beams of a few keV using purely electrostatic fields and provides a large field-free region where the stored ions oscillate. A photomultiplier working in the single-photon counting mode was used to observe the 380 nm photons arising from the magnetic dipole $\mathrm{}\left(M1\mathrm{}\right)\mathrm{}$ transition ${}^1{\overrightarrow{S_0}}^3{P}_1$ of ${\mathrm{Xe}}^{2+}.$ The present measurement yields a value of $4.46\pm 0.08\hspace{0.5em}\mathrm{ms},$ which is in good agreement with previous measurements, but is almost four times more accurate.

A molecular jet-expansion beam of ZnNe seeded in Ne was crossed with a pulsed-laser beam produced by a Nd:YAG (yttrium aluminum garnet) laser-pumped dye laser. The dye laser was frequency doubled with a BBO-C second-harmonic-generation (SHG) crystal. Both the dye laser and the SHG were synchronously scanned over a range of $\lambda =2130\mathrm{}–2170\AA$ in the vicinity of the Zn atomic $4{}^1{P}_1–4{}^1{S}_0$ resonance line (2138.65 Å), producing an excitation spectrum related to the $D1\left(4\mathrm{}{}^1{P}_1\right)\leftarrow {X0\mathrm{}}^{+}\left(4\mathrm{}{}^1{S}_0\right)$ transition in the ZnNe molecule. The spectral traces, which show a pronounced vibrational structure, were subjected to LeRoy’s near-dissociation expansion (NDE) analysis, yielding ${\omega }_e,$ ${\omega }_e{x}_e,$ $D_e,$ and long-range molecular potential parameters. Computer simulation of the excitation spectrum, based on a calculation of the Franck-Condon factors, yielded additional information on the equilibrium internuclear separation for the $D1\mathrm{}$ and ${X0\mathrm{}}^{+}$ states. The NDE analysis provided long-range characteristics for the ${X0\mathrm{}}^{+}$ state of the CdNe and HgNe molecules as well. A simple dispersive model, and a combination rule for van der Waals interactions in the ground state of ZnNe, CdNe, and HgNe molecules, are discussed.

We have investigated double electron capture with simultaneous target ionization in collisions of 25-keV/amu ${}^3{\mathrm{He}}^{2+}$ projectiles on argon. Doubly differential cross sections for electrons emitted in angles $0°,20°,$ $45°,90°,$ $128°,175°,$ in coincidence with the neutralized projectiles were obtained. To establish the relative importance of the double capture channel in the electron emission at the present intermediate impact velocity, differential cross sections for total electron emission were also measured. A narrow symmetric cusp-shaped structure for electrons with velocity close to the ion velocity, associated with the neutral emerging projectile, is observed. Binary encounter electrons, masked by other processes in total emission, are clearly observed for the double capture plus ionization channel.

We have measured the ratio of the intensity of the $n=\overrightarrow{3}1$ intercombination line $(1s3p{}^3{P}_1\to {1s}^2{}^1{S}_0)$ to that of the resonance line $(1s3p{}^1{P}_1\to {1s}^2{}^1{S}_0)$ for the heliumlike ions ${\mathrm{Mg}}^{10+},$ ${\mathrm{Al}}^{11+},$ ${\mathrm{Ar}}^{16+},$ ${\mathrm{Ti}}^{20+},$ ${\mathrm{V}}^{21+},$ ${\mathrm{Cr}}^{22+},$ and ${\mathrm{Fe}}^{24+}.$ The measurements were carried out on the Lawrence Livermore National Laboratory electron-beam ion trap using electron-beam energies mostly near the threshold for the direct excitation of the resonance line, or near the threshold for excitation of the $n=4\mathrm{}$ levels, to avoid populating the $n=3\mathrm{}$ levels by cascades from levels with $n>~5.$ High-resolution Bragg crystal spectrometers in curved as well as flat geometry were used to record the x rays. The measured ratios have been compared to predicted values, which were found to underestimate the measured values.

The multielectron ionization and Coulomb explosion of ${\mathrm{Xe}}_{55},$ ${\mathrm{Xe}}_{249},$ ${\mathrm{Xe}}_{531},$ and ${\mathrm{Xe}}_{1061}$ clusters in a strong laser field is studied using classical dynamics simulations, which describe the motion of unbound electrons and ions. The generation of the unbound electrons is described as the removal of bound electrons from their host atoms (ions) by the electrostatic barrier suppression or collisional ionization. According to the results of simulations performed for the laser power ${10}^{16}{\mathrm{W}/\mathrm{c}\mathrm{m}}^2$ and frequency 0.386 ${\mathrm{fs}}^{\mathrm{-}1}$, almost all unbound electrons are removed from the clusters. In large ${\mathrm{Xe}}_{531}$ and ${\mathrm{Xe}}_{1061}$ clusters, electrons are removed mainly when the size of the clusters is enlarged due to Coulomb explosion. The quasiresonance energy enhancement is shown to be mainly responsible for the removal of electrons from the clusters. The energy enhancement process is hampered by electron-electron and electron-ion collisions.

Na clusters in the size range of 50–400 atoms are led to evaporate in a heat bath with controlled temperature. For cluster sizes around closed shells, decay rates are determined as a function of temperature. For temperatures below 357 K they all agree with an Arrhenius law and allow absolute separation energies to be extracted. Separation energies are presented and compared to previously determined (relative) values. Enhanced shell effects are observed in the heat bath experiments. Deviations from the Arrhenius law at intermediate temperatures are discussed.

Using a model potential approach, we study the time-dependent behavior of a Bose-Einstein condensate with negative scattering length during its collapse in the zero-temperature limit. The condensate is modeled through an effective potential, which linearizes the Schrödinger equation, in order to obtain an intuitive visualization of the dynamics of the condensate. We find that a substantial fraction of the condensate survives the collapse. The origin for this survival is the reappearance of a barrier in the effective potential during the collapse. In contrast to previous calculations, the present calculations indicate that the size of the residual condensate strongly depends on the growth rate of the condensate. The present results are compared to other theoretical calculations and to experimental work.