A theoretical model is developed for the description of the single-electron emission from surfaces following the impact of fast ions. The theory describes quantum mechanically the ion reflection at the surface and the excitation of the valence band electrons via an ion-electron interaction renormalized by the dielectric response of the target. Numerical calculations are presented and analyzed for the electron emission from the conduction band of an aluminum surface upon proton impact. Particular attention is devoted to the influence of the dielectric screening on the energy distributions and the angular distributions of the ejected electrons. In addition, the role of the surface electronic structure is studied.

A model potential for the general Rydberg atom is put forward, which includes not only the Coulomb interaction potential and the core-attractive potential, but also the exchange potential between the excited electron and other electrons. Using the region-splitting consistent and iterative method, we calculated the scaled recurrence spectra of the helium atom in parallel electric and magnetic fields and the closed orbits in the corresponding classical system have also been obtained. In order to remove the Coulomb singularity of the classical motion of Hamiltonian, we implement the Kustaanheimo-Stiefel transformation, which transforms the system from a three-dimensional to a four-dimensional one. The Fourier-transformed spectra of the helium atom has allowed direct comparison between peaks in such a plot and the scaled action values of closed orbits. Considering the exchange potential, the number of the closed orbits increased, which led to more peaks in the recurrence spectra. The results are compared with those of the hydrogen case, which shows that the core-scattered effects and the electron exchange potential play an important role in the multielectron Rydberg atom.

We discuss the theory of mixtures of bosonic and fermionic atoms in periodic potentials at zero temperature. We derive a general Bose-Fermi Hubbard Hamiltonian in a one-dimensional optical lattice with a superimposed harmonic trapping potential. We study the conditions for linear stability of the mixture and derive a mean-field criterion for the onset of a bosonic superfluid transition. We investigate the ground-state properties of the mixture in the Gutzwiller formulation of mean-field theory, and present numerical studies of finite systems. The bosonic and fermionic density distributions and the onset of quantum phase transitions to demixing and to a bosonic Mott-insulator are studied as a function of the lattice potential strength. The existence is predicted of a disordered phase for mixtures loaded in very deep lattices. Such a disordered phase possessing many degenerate or quasidegenerate ground states is related to a breaking of the mirror symmetry in the lattice.

We performed experimental and theoretical analyses of a correlation between pump pulse propagation and harmonic yield in Ar and Xe, in a long static gas cell, at high pumping energies, for loose focusing geometry, using 35-fs pulses from a Ti:sapphire laser. Axial and transverse profiles of the plasma column were measured under several experimental conditions with the aim of characterizing the pulse propagation. From the plasma fluorescence profiles observed, it was found that self-guided propagation of the pump pulse in Xe resulted in the channel formation. A three-dimensional nonadiabatic propagation model was used to calculate the field configuration in the interaction region and to explain the channel formation. A model developed to calculate the transverse plasma profiles can adequately reproduce the experimental data and confirm the channel formation. Correlated measurements of harmonics generation reveal that channel formation greatly enhances the harmonic yield as harmonics propagate under phase-matched conditions.

Quantum teleportation of qudits is revisited. In particular, we analyze the case where the quantum channel corresponds to a nonmaximally entangled state and show that the success of the protocol is directly related to the problem of distinguishing nonorthogonal quantum states. The teleportation channel can be seen as a coherent superposition of two channels, one of them being a maximally entangled state, thus leading to perfect teleportation, and the other, corresponding to a nonmaximally entangled state living in a subspace of the d-dimensional Hilbert space. The second channel leads to a teleported state with reduced fidelity. We calculate the average fidelity of the process and show its optimality.

In view of the current interest in trapping antihydrogen $\overline{\mathrm{H}}$ atoms below 1 K, the s-wave elastic-scattering parameters for the antihydrogen scattering off atomic helium target are calculated in the energy range $1\times {10}^{-16}–1\times {10}^{-2}\mathrm{a}.\mathrm{u}.\mathrm{}$ using close-coupling models. The predicted cross section will help to simulate the evolution of a realistic mixture of He and ${\mathrm{H}}_2$ through the process involving ejection of $\overline{\mathrm{H}}$ from the trap. The trend of the present results with different basis sets conclusively indicates the reliability of the predicted results.

The Hooke’s-law atom (hookium) provides an exactly soluble model for a two-electron atom in which the nuclear-electron Coulombic attraction has been replaced by a harmonic one. Starting from the known exact position-space wave function for the ground state of hookium, we present the momentum-space wave function. We also look at the intracules, two-electron probability distributions, for hookium in position, momentum, and phase space. These are compared with the Hartree-Fock results and the Coulomb holes (the difference between the exact and Hartree-Fock intracules) in position, momentum, and phase space are examined. We then compare these results with analogous results for the ground state of helium using a simple, explicitly correlated wave function.

A possibility for fundamental constants to vary in time is suggested by theories unifying gravity with other interactions. In this article we examine proposals to use optical transitions of Sr, Dy, Yb II, and Yb III for the search of the time variation of the fine-structure constant $\alpha .$ Frequencies of atomic transitions are calculated using the relativistic Hartree-Fock method and configuration interaction technique. The effect of variation of $\alpha$ on the frequencies is studied by varying $\alpha$ in computer codes. Accuracy of measurements needed to improve the current best limit on the time variation of $\alpha$ is discussed.

Stripping cross sections in nitrogen have been calculated using the classical trajectory approximation and the Born approximation of quantum mechanics for the outer shell electrons of 3.2 GeV ${\mathrm{I}}^{-}$ and ${\mathrm{Cs}}^{+}$ ions. A large difference in cross section, up to a factor of 6, calculated in quantum mechanics and classical mechanics, has been obtained. Because at such high velocities the Born approximation is well validated, the classical trajectory approach fails to correctly predict the stripping cross sections at high energies for electron orbitals with low ionization potential.

Modified Kramers-Kronig relations and corresponding sum rules are shown to hold for the total refractive index that can be presented as a sum of complex linear and nonlinear refractive indices, respectively. It is suggested that a self-action process, involving the degenerate third-order nonlinear susceptibility, can yield a negative total refractive index at some spectral range.

We present reduction theorems for the problem of optimal unambiguous state discrimination of two general density matrices. We show that this problem can be reduced to that of two density matrices that have the same rank n and are described in a Hilbert space of dimensions $2n.$ We also show how to use the reduction theorems to discriminate unambiguously between N mixed states $(N>~2).$

We study the mathematical structure of superoperators describing quantum measurements, including the entangling measurement—the generalization of the standard quantum measurement that results in entanglement between the measurable system and apparatus. It is shown that the coherent information can be effectively used for the analysis of such entangling measurements whose possible applications are discussed as well.

Low-energy ion scattering is very surface sensitive if scattered ions are analyzed. By time-of-flight (TOF) techniques, the neutral and the charge-integrated spectra (ions plus neutrals) are obtained, which yield information about deeper layers. It is well known that charge integrated spectra may exhibit a surface peak which is more pronounced for heavier projectiles, e.g., Ne ions. Aiming at a more profound physical understanding of this surface peak, we performed TOF experiments and computer simulations for H, He, and Ne projectiles scattered from a polycrystalline copper target. Measurements were done in the range of 1–9 keV for a scattering angle of $129°$ under UHV conditions. The simulations were performed using the MARLOWE code for the given experimental parameters and a polycrystalline target. In the experiments, a pronounced surface peak was observed at low energies, which fades away at higher energies. This peak is quantitatively reproduced by the simulation. Several atomic layers may contribute to the surface peak, depending on the energy. Analyzing the contributions of the individual outermost atomic layers, one finds that the binary collisions of the projectiles with atoms in the first and the second layer yield a narrow energy distribution, while the contribution from the deeper layers is dominated by multiple scattering and therefore exhibits a very broad energy spectrum. It is shown that the appearance of a more or less pronounced surface peak is due to the relative contributions of single scattering and multiple scattering and thus depends on the projectile energy and mass.

We theoretically study the influence of the noise strength on the excitation of the Brillouin propagation modes in a dissipative optical lattice. We show that the excitation has a resonant behavior for a specific amount of noise corresponding to the precise synchronization of the Hamiltonian motion on the optical potential surfaces and the dissipative effects associated to optical pumping in the lattice. This corresponds to the phenomenon of stochastic resonance. Our results are obtained by numerical simulations and correspond to the analysis of microscopic quantities (atomic spatial distributions) as well as macroscopic quantities (enhancement of spatial diffusion and pump-probe spectra). We also present a simple analytical model in excellent agreement with the simulations.

We describe a method to couple a light pulse into a cavity with arbitrarily high finesse, with an efficiency that in theory can approach 100% even if the pulse duration is much longer than the round-trip time of the cavity. The spectrum of the pulse is compressed into a single narrow mode in an adiabatic and reversible way. The method uses an input coupler with a variable effective reflectivity which is adapted to match the known temporal shape of the pulse. In addition to a theoretical description of the method, we demonstrate the principle experimentally.

Complex physical systems contain information which, under some well-defined processes can differentiate between local and nonlocal information. Both these fundamental aspects of information are defined operationally. Local information is locally accessible and allows one to perform processes, such as physical work, while nonlocal information allows one to perform processes such as teleportation. It is shown that these two kinds of information are complementary in the sense that two parties can either gain access to the nonlocal information or to the local information but not both. This complementarity has a form similar to that expressed by entropic uncertainty relations. For pure states, the entanglement plays the role of Planck’s constant. We also find another class of complementarity relations which applies to operators and is induced when two parties can only perform local operations and communicate classical (LOCC). In particular, observables such as the parity and phase of two qubits commute but under LOCC, they are complementary observables. It is also found this complementarity is pure in the sense that it can be “decoupled” from the uncertainty principle. It is suggested that these complementarities represent an essential extension of Bohr’s complementarity to complex (distributed) systems which are entangled.

A marked state can be found with certainty in the two-qubit case of Grover’s algorithm. This property is included in the proposed quantum secret-sharing protocol. In the proposed scheme, the sender prepares some initial state in private and then performs a phase shift of the marked state as the sender’s bit. Then, the sender sends these two qubits to each of the two receivers. Only when the sender broadcasts the initially prepared state and then the receivers perform the corresponding inversion operation about the average, is the sender’s bit faithfully revealed. Moreover, the sender can detect deception using cheat-detecting states. The proposed quantum secret-sharing protocol is shown to be secure.

A quantum model for singly resonant second-harmonic generation in a cavity with transverse degrees of freedom is analyzed. An instability threshold for pattern formation exists in this system. Below threshold, a strong modulation of the noise is demonstrated in the transverse structure of the far field. The performed analysis encompasses both one- and two-point correlation functions. The noise in a single far-field point is generally above the classical vacuum noise level. In contrast, strong nonclassical two-point correlations are encountered between opposite emission directions in the far field. For the fundamental field the correlations are shown to be of the Einstein-Podolsky-Rosen type, thus establishing a remarkable analog to the quantum correlations found in a nondegenerate optical parametric oscillator.

A time-dependent perturbation method is proposed to study the properties of the frequency-modulated excitation of a potassium atom. Rabi oscillations in the absence of a modulation, square-wave oscillations in the presence of slow modulation, and radio-frequency multiphoton resonances in the presence of fast modulation have been calculated using this method. The numerical results are in excellent agreement with those of the experiment; novel explanations have been given to understand some of the experimental results.

This paper focuses on the geometric phase of entangled states of bipartite systems under bilocal unitary evolution. We investigate the relation between the geometric phase of the system and those of the subsystems. It is shown that (1) the geometric phase of cyclic entangled states with nondegenerate eigenvalues can always be decomposed into a sum of weighted nonmodular pure state phases pertaining to the separable components of the Schmidt decomposition, although the same cannot be said in the noncyclic case, and (2) the geometric phase of the mixed state of one subsystem is generally different from that of the entangled state even if the other subsystem is kept fixed, but the two phases are the same when the evolution operator satisfies conditions where each component in the Schmidt decomposition is parallel transported.