We propose a simple scheme for the quantum teleportation of both bipartite and multipartite entangled coherent states with the success probability 1/2. The scheme is based only on linear optical devices such as beam splitters and phase shifters, and two-mode photon number measurements. The quantum channels described by the multipartite maximally entangled coherent states, are readily made by the beam splitters and phase shifters.

We characterize and classify quantum correlations in two-fermion systems having $2K$ single-particle states. For pure states we introduce the Slater decomposition and rank (in analogy to Schmidt decomposition and rank); i.e., we decompose the state into a combination of elementary Slater determinants formed by pairs of mutually orthogonal single-particle states. Mixed states can be characterized by their Slater number which is the minimal Slater rank required to generate them. For $K=2\mathrm{}$ we give a necessary and sufficient condition for a state to have a Slater number 1. We introduce a correlation measure for mixed states which can be evaluated analytically for $K=2.\mathrm{}$ For higher $K,$ we provide a method of constructing and optimizing Slater number witnesses, i.e., operators that detect Slater numbers for some states.

Electron-hydrogen scattering, within the S-wave model, is considered at total energies ranging from 1 through to 7 Ry. Scattering cross sections are presented from initial ground and excited states with particular attention given to the case where the initial state is in the continuum. An unexpected minimum is found in the elastic free-free cross section.

We investigate a simply corrected Keldysh-Faisal-Reiss (KFR) rate formula for laser-induced ionization of atoms in the nonperturbative intensity domain. Predictions of the formula are compared, first, with ab initio Floquet calculations, which show good agreement in the nonperturbative intensity domain for not too short wavelengths. Second, they are found to agree with the results of numerical simulations for the H atom, provided the pulse lengths are not shorter than three field cycles, so that the adiabatic rate becomes a valid parameter. Finally, total single-ionization yields predicted by the present model are compared with 36 different experimental data sets for He, Ne, Ar, Kr, and Xe, covering both linear and circular polarizations, and different wavelengths, pulse durations, and intensities; the results show a remarkable overall agreement with the data.

For some potentials, such as the Hulthén and Yukawa potentials, the number of possible bound states depend on an internal potential parameter. Even if the parameters are chosen such that no bound state exists, resonances occur after coupling these systems to the continuum, e.g., by an additional external electric field. We will discuss those resonances which have no bound predecessor. The computations are based on complex coordinate rotations and finite elements.

The hydrogen molecule in the presence of a homogeneous magnetic field is investigated for the parallel configuration in the complete regime of field strengths $B=0\mathrm{}-100$ a.u. Up to seven excitations are studied for gerade as well as ungerade spin triplet states of $\Sigma$ symmetry with a high accuracy. The evolution of the potential-energy curves for the individual states with increasing field strength as well as the overall behavior of the spectrum are discussed in detail. A typical feature of many potential-energy curves is the strong increase of the dissociation energy and decrease of the corresponding equilibrium internuclear distance in the high-field regime. Strong qualitative changes of the potential energies are found particularly within the regime $0.01<~B<~5$ a.u., where we observe among other things the field-dependent evolution of patterns of avoided crossings.

We use a variational method to investigate the ground-state phase diagram of a small, asymmetric Bose-Einstein condensate with respect to the dimensionless interparticle interaction strength $\gamma$ and the applied external rotation speed $\Omega .$ For a given $\gamma ,$ the transition lines between no-vortex and vortex states are shifted toward higher $\Omega$ relative to those for the symmetric case. We also find a re-entrant behavior, where the number of vortex cores can decrease for large $\Omega .$ In addition, stabilizing a vortex in a rotating asymmetric trap requires a minimum interaction strength. For a given asymmetry, the evolution of the variational parameters with increasing $\Omega$ shows two different types of transitions (sharp or continuous), depending on the strength of the interaction. We also investigate transitions to states with higher vorticity; the corresponding angular momentum increases continuously as a function of $\Omega .$

The Dirac-matrix representation of a general two-qubit system is shown to exhibit quite interesting features. The relativistic symmetries of time reversal T, charge conjugation C, parity P, and their products are reinterpreted here by examining their action on the Bell states. It is shown that only C does not mix the Bell states whereas all others do. The various logic gates of quantum information theory are also expressed in terms of the Dirac matrices. For example, the NOT gate is related to the product of T and P. A two-qubit density matrix is found to be entangled if it is invariant under C.

Temporal character of cone emission from Sr vapor excited with ∼3-ns, near-resonant laser pulses is studied with ∼0.5-ns resolution. The cone pulses appear significantly narrower than the laser pulse. Their properties (amplitude, width, energy, delay, and angular distribution) systematically depend on the laser energy and detuning in a way that contradicts present, steady-state models of cone emission.

We consider unitary dynamical evolutions on n qubits caused by time-dependent pair-interaction Hamiltonians and show that the running time of a parallelized two-qubit gate network simulating the evolution is given by the time integral over the chromatic index of the interaction graph. This defines complexity measures of continuous and discrete quantum algorithms, which are in exact one-to-one correspondence. We prove a lower bound on the complexity of those multiparticle states, which show quantum superpositions on the macroscopic scale.

We have studied the pair-correlation function, the exchange-correlation hole, and the exchange-correlation energy density of the valence electrons in the Si atom using the Coulomb-coupling constant integration technique with the variational quantum Monte Carlo method. These quantities are compared to those derived from various approximate models within the Kohn-Sham density functional theory. We find that the charge density prefactor in the expression for the exchange-correlation hole dominates the errors found in the local spin density approximation (LSDA), that the generalized gradient approximation improves energy calculations by improving the LSDA at long ranges, and that the weighted spin density approximation, which uses the correct charge density prefactor, gives the lowest root mean square error for the exchange-correlation energy density.

We present a variational basis-set calculational scheme for elastic scattering of positronium atom by helium atom in S wave and apply it to the calculation of the scattering length. Highly correlated trial functions with appropriate symmetry are used in this calculation. We report numerical result for the scattering length in atomic unit: $(1.0\mathrm{}\pm {0.1)a}_0.$ This corresponds to a zero-energy elastic cross section of $(4.0\mathrm{}\pm 0.8)\pi a_0^2.$

Xe II fluorescence, following the resonant Auger decay of the ${\mathrm{Xe}}^{*}$ ${4d}_{5/2}^{-1}6p$ photoexcited state, has been measured in the wavelength region 400 nm $<~\lambda$ (fluo) $<~610$ nm by means of dispersed fluorescence spectroscopy, and the degree of linear polarization of the emitted light has been analyzed. From these data, the alignment of the ionic ${5p}^{4}6p$ states produced by the Auger decay has been determined by taking into account the depolarization of the radiatively decaying Xe II multiplet due to cascade population and hyperfine interactions. Calculations of the alignment are performed in a multiconfigurational Dirac-Fock approach and compared with the experiment. Good agreement between experiment and theory has been obtained for almost all fine-structure components of the Xe II ${5p}^{4}6p$ multiplet, providing reliable alignment parameters of the ionic states produced upon resonant Auger decay.

We report the experimental realization of coherent population transfer from the $2{}^{3}S$ state to $2{}^{3}P$ fine-structure levels of helium, using the technique of hyper-Raman adiabatic passage, in which the pump-laser coupling involves a two-photon transition. We discuss the dependence of population transfer upon pump and Stokes detunings, and show that by suitably setting the detunings one can transfer population efficiently as either a two-step process to final states or as a single-step two-photon transition to an intermediate state. We use an adiabatic-state picture to interpret these experimental results. Since the optimum detuning depends on the pump laser intensity the transfer efficiency is compromised by the variation of the intensity across the spatial profile of the laser beam. Our experimental data agree well with numerical simulation based on density-matrix equations, including all 15 magnetic sublevels.

The dynamics of a two-electron system in a strong laser pulse is described by the time-dependent extended Hartree-Fock (TDEHF) scheme. Ionization yields for a one-dimensional helium model are calculated and compared with results of exact calculations (full correlation) and time-dependent Hartree-Fock calculations (no correlation). The knee structure in the double-ionization curve appears also for the TDEHF calculations, but the yields are more than an order of magnitude too low. The total ionization probability agrees well with the exact results, and much improved results for the single-ionization yields are obtained. Due to the reduced dimensionality of the model, the TDEHF ground state consists of a left and right orbital. While one of the orbitals easily transforms into a continuum state, the other remains localized and screens the nucleus. In this manner, even the one-dimensional orbitals can be considered to be “inner” and “outer” orbitals.

Quantum-mechanical calculations of multiphoton double ionization by intense laser pulses show that the total-kinetic-energy spectrum of the photoelectrons consists of peaks separated by the photon energy, analogous to ordinary above-threshold ionization. Related structures appear in the two-electron and in the recoil-ion momentum distribution. We propose a method to extract the total-kinetic-energy spectrum from the experimental recoil-ion spectrum.

We study the quantum dynamics of two interacting electrons confined in a Penning trap. We determine the characteristic frequencies of this system and we propose a way to perform measurement on spin and cyclotron degrees of freedom as well as a way of preparing the geonium atom in any spin state.

We report on a method for optimizing the collection of entangled photon pairs in type-II parametric fluorescence. With this technique, we detected 360 000 polarization-entangled photon pairs per second in the near-ir region in single-mode optical fibers. The entanglement of the photon pairs was verified by measuring polarization correlations in different bases of at least 96%.

Multiphoton resonances with ponderomotively upshifted Rydberg states are believed to have dramatic effects on the plateau of high-order above-threshold ionization. For short pulses and intense laser fields, individual Rydberg states lose their physical significance. Under these conditions, on the basis of experimental and theoretical investigation of the dependence of the photoelectron spectra on the laser intensity, we propose that the observed effects can be largely understood in terms of the channel closings that are characteristic of a short-range model potential.