The fragmentation of the ${\mathrm{CD}}_4$ molecule after selective ionization of the ${1t}_2$ and ${2a}_1$ electrons with photons from 70 to 290 eV has been studied with the energy-resolved electron-ion coincidence technique. The mass spectra acquired in coincidence with ${1t}_2$ electrons reveal ${\mathrm{CD}}_4^{+},$ ${\mathrm{CD}}_3^{+},$ and ${\mathrm{CD}}_2^{+}$ fragments, depending on the excitation energy used. The production of ${\mathrm{CD}}_3^{+}$ is strongly enhanced after C $1s$ excitation to different core excited states, with respect to the production observed after direct ionization of the ${1t}_2$ orbital. This enhancement is correlated with the changes of the molecular geometry when it relaxes from the core-excited state.

The charge-state distribution following the ${\beta }^{+}$ decay ${\mathrm{of}}^{21}\mathrm{Na}$ has been measured, showing a larger than expected fraction of the daughter ${}^{21}\mathrm{Ne}$ in positive charge states. No dependence on either the ${\beta }^{+}$ or recoil nucleus energy is observed. The data are compared to a simple model based on the sudden approximation. Calculations suggest that a small but important contribution from recoil ionization has significant consequences for precision $\beta$ decay correlation experiments detecting recoil ions.

We introduce a distorted wave method to calculate the nonlinear excitation effects occurring when a fast bare ion penetrates a free-electron gas. The central scheme of this work is to replace the undistorted plane waves leading to the Lindhard dielectric response function (or random phase approximation) by Coulomb waves with an effective charge. This impulse-type approximation is valid for velocities larger than the Fermi velocity. Stopping and mean free path are presented for impact of bare multicharged ions on aluminum free-electron gas. The Barkas effect is theoretically found, i.e., negative heavy particles lose energy at the lower rate than positive particles of the same velocity do. As the projectile charge increases, the single differential cross section per unit energy presents two effects: the plasmon peak sharpens and the binary peak starts to be increasingly noticeable.

Picosecond “half-cycle” pulses (HCPs) have been used to produce electronic wave packets by recombining photoelectrons with their parent ions. The time-dependent momentum distributions of the bound wave packets are probed using a second HCP and the impulsive momentum retrieval (IMR) method. For a given delay between the initial photoionization event and the HCP recombination, classical trajectory simulations predict pronounced periodic wave packet motion for a restricted range of recombining HCP amplitudes. This motion is characterized by the repeated formation and collapse of a highly localized spike in the three-dimensional electron probability density at a large distance from the nucleus. Our experiments confirm that oscillatory wave packet motion occurs only for certain recombination “kick” strengths. Moreover, the measured time-dependent momentum distributions are consistent with the predicted formation of a highly localized electron packet. We demonstrate a variation of the IMR in which amplitude modulation of the HCP probe field is employed to suppress noise and allow for a more direct recovery of electron momentum from experimental ionization data.

The finite temperature Green’s function technique is used to calculate the energies and damping rates of the elementary excitations of homogeneous, dilute, spin-1 Bose gases below the Bose-Einstein condensation temperature in both the density and spin channels. For this purpose a self-consistent dynamical Hartree-Fock model is formulated, which takes into account the direct and exchange processes on equal footing by summing up certain classes of Feynman diagrams. The model is shown to satisfy the Goldstone theorem and to exhibit the hybridization of one-particle and collective excitations correctly. The results are applied to gases of ${}^{23}\mathrm{Na}$ and ${}^{87}\mathrm{Rb}$ atoms.

The dynamics of Bose-Einstein condensates trapped in a deep optical lattice is governed by a discrete nonlinear equation (DNL). Its degree of nonlinearity and the intersite hopping rates are retrieved from a nonlinear tight-binding approximation taking into account the effective dimensionality of each condensate. We derive analytically the Bloch and the Bogoliubov excitation spectra and the velocity of sound waves emitted by a traveling condensate. Within a Lagrangian formalism, we obtain Newtonian-like equations of motion of localized wave packets. We calculate the ground-state atomic distribution in the presence of a harmonic confining potential, the frequencies of small amplitude dipole, and quadrupole oscillations. We finally quantize the DNL, recovering an extended Bose-Hubbard model.

Using the classical trajectory Monte Carlo method, we calculated the charge-transfer cross section for antiprotons colliding with Rydberg positronium, leading to antihydrogen formation. The results show a significant influence of an externally applied magnetic field which causes a reduction of the cross section.

A one-mirror random laser is described. The necessary feedback is from random scattering inside a disordered medium and a reflective mirror together. With such a half-random and half-conventional cavity, the lasing threshold can be reduced dramatically, especially for systems in the localized regime, where the lasing threshold is otherwise very difficult to reach by optical pumping. The threshold decrease is due to better overlap between the pumped region and lasing modes, as well as the different eigenmode structure of the half-close system. An Anderson-type lattice Hamiltonian model was used to investigate the decay rate distributions in one-dimensional systems open at one end and at both ends. Analysis on the small decay rate tail showed an enhancement of localization in the former kind of systems.

We provide a general, necessary, and sufficient condition for the possibility of transforming a mixed bipartite Gaussian state with arbitrarily many modes to another one under arbitrary local Gaussian channels, which do not include classical communication. Moreover, by means of this condition we present a necessary criterion that can be used to check the possibility of a state transformation between two mixed Gaussian states. At the same time, we prove that our criterion can be reduced to the Eisert-Plenio criterion when the mode number is chosen as 1 per side.

The discovery of entangled quantum states from which one cannot distill pure entanglement constitutes a fundamental recent advance in the field of quantum information. Such bipartite bound-entangled (BE) quantum states could fall into two distinct categories: (1) Inseparable states with positive partial transposition (PPT), and (2) states with negative partial transposition (NPT). While the existence of PPT BE states has been confirmed, only one class of conjectured NPT BE states has been discovered so far. We provide explicit constructions of a variety of multicopy undistillable NPT states, and conjecture that they constitute families of NPT BE states. For example, we show that for every pure state of Schmidt rank greater than or equal to 3, one can construct n-copy undistillable NPT states, for any $n>~1.$ The abundance of such conjectured NPT BE states, we believe, considerably strengthens the notion that being NPT is only a necessary condition for a state to be distillable.

In this paper, we study the generation of entanglement by interaction-free measurements. Using Kwiat et al.’s interferometer, we construct a two-qubit quantum gate that changes one particle’s trajectory according to the other particle’s trajectory. We propose methods for generating the Bell state from an electron and a positron and from a pair of photons using this gate. We also show that, by using this gate, we can carry out the Bell measurement with a probability of 3/4 at the maximum and execute a controlled-NOT operation by the method proposed by Gottesman and Chuang with a probability of 9/16 at the maximum. We estimate the success probability for generating the Bell state by our procedure under imperfect interaction.

We propose a protocol for teleporting an unknown coherent-state superposition within a network consisting of $2^N$ parties with N an arbitrary positive integer. We show explicitly that for moderate and high intensity fields the probability of success is 50%, i.e. the same as in the case of $N=1.\mathrm{}$

A method for quantum computation in the presence of spontaneous emission is proposed. The method combines strong and fast (dynamical decoupling) pulses and a quantum error correcting code that encodes n logical qubits into only $n+1\mathrm{}$ physical qubits. Universal, fault-tolerant, quantum computation is shown to be possible in this scheme using Hamiltonians relevant to a range of promising proposals for the physical implementation of quantum computers.

The Bell–Clauser-Horne-Shimony-Holt (BCHSH) inequality (in terms of correlation functions) of two qutrits is studied in detail by employing tritter measurements. A uniform formula for the maximum value of this inequality for tritter measurements is obtained. Based on this formula, we show that nonmaximally entangled states violate the BCHSH inequality more strongly than the maximally entangled one. This result is consistent with what was obtained by Acín et al. [Phys. Rev. A $65,$ 052325 (2002)] using the Bell–Clauser-Horne inequality (in terms of probabilities).

O $1s$ single-hole ionization cross sections of CO have been measured for $v^{\prime }=0\mathrm{}-2.$ The O ${1s}^{-1}{\sigma }^{*}$ shape resonance moves up in energy with an increase in $v^{\prime },$ opposite to the C ${1s}^{-1}{\sigma }^{*}$ shape resonance observed previously. Theoretical calculations beyond the fixed-nuclei approximation reproduce these experimental results. The relationship between the $v^{\prime }$-dependent characteristic internuclear distance in the residual ion and the shape resonance energy is discussed.

We calculate the natural decay rates of Rydberg atoms in strong magnetic fields. We use adiabatic basis sets that exploit the different time scales of the electronic motion parallel and transverse to the magnetic field. For large absolute values of the azimuthal quantum number m, our approach is very efficient and naturally leads to a classification of the decay modes into magnetron, z-bounce, and cyclotron decays. We discuss the dependence of the decay rates on m, and study the enhancement of the decay rates due to thermal radiation.

The $K\alpha$ x-ray emission spectra of Si bombarded by 1–3-MeV protons were measured with a crystal spectrometer in Johansson geometry, enabling energy resolution below the natural linewidth of the measured $K\alpha$ line. The $K\alpha L^1$ and $K\alpha L^2\left(K\alpha L^{1,2}\right)$ x-ray satellite lines appearing in these spectra as a result of the radiative decay of atomic states with one hole in the $K$ shell and one or two in the $L$ subshells were precisely measured. The energies and intensities of the main components that could be resolved within the satellite lines are given. It has been demonstrated that the latter do not depend on proton energy and are essentially the same as in photon-induced spectra. The overall $K\alpha L^1$ satellite intensity relative to the $K\alpha$ diagram line has been used to deduce the $L$-shell ionization probabilities induced in near-central proton collisions. The experimental values were compared to the theoretical values calculated with the semiclassical approximation, with the three-body classical trajectory Monte Carlo model, and the classical binary-encounter-based geometrical model.

The photoionization cross section of the ground $\left(\right[\mathrm{Ne}]{3s}^2{3p}^{6}3d$ ${}^2{D}_{3/2})$ and first two metastable $\left(\right[\mathrm{Ne}]{3s}^2{3p}^{6}3d$ ${}^2{D}_{5/2}$ and $\left[\mathrm{Ne}\right]{3s}^2{3p}^{6}4s$ ${}^2{S}_{1/2})$ levels of potassiumlike Sc III have been studied using fully relativistic R-matrix method. To show the effects of configuration interaction on the cross section, we first perform a nonrelativistic R-matrix calculation. The detailed structures and resonances of the cross section obtained by the fully relativistic method in the region of $3\overrightarrow{p}3d$ and $3\overrightarrow{p}4s$ resonances are described and analyzed in some detail. The positions, autoionization widths, and oscillator strengths of some prominent resonances are determined. The calculated cross section is compared with a recent experiment [S. Schippers et al., Phys. Rev. Lett. 89, 193002 (2002)]. The resonance energies and intensities predicted by the fully relativistic calculations agree well with the experiment, especially for the $3\overrightarrow{p}4s$ resonances in the region of lower photon energy, while it is not so satisfactory for the nonrelativistic calculations. Our results show that not only adequate configuration interaction, particularly the ${3p}^3\to {3d}^3$ core-valence correlations, but also relativistic effects should be carefully included in the calculation to obtain a good agreement with the experiment.

An optical mask is a standing wave of light in resonance with an open atomic transition. The mask depletes the population of the initial internal state everywhere except in a narrow vicinity of the nodes. We have experimentally explored the optical mask as a tool for creating a periodic pattern in the density of cold rubidium atoms (in a particular hyperfine ground state) and also as an instrument for imaging the density in situ. The instrumental width of the imaging technique is a small fraction of the optical wavelength and is limited due to an effect of the dipole force rather than the initial velocity spread.

We present a numerical study on the influence of Pauli’s exclusion principle in the double ionization of helium in strong laser fields. To this end, we compare the ionization dynamics of the helium in its triplet and singlet configurations. The symmetric character of the electronic orbital wave-function affects strongly the mechanism of ionization in helium. In particular, it is found that the double ionization is partially suppressed in the ortho-helium case. The mechanisms relevant for this suppression are discussed.