Table of contents

Journal of Physics B: Atomic, Molecular and Optical Physics invites you to submit a paper to a forthcoming special issue on Light Control at the Nanoscale to appear in 2007.

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A generalized ADK (Ammosov–Delone–Krainov) theory for ionization of open-shell atoms is compared to ionization experiments performed on the transition metal atoms V, Ni, Pd, Ta and Nb. Our theory is found to be in good agreement for V, Ni, Pd and Ta, whereas conventional ADK theory overestimates ionization by orders of magnitude. The key to understanding the observed ionization reduction is the angular momentum barrier. Our analysis shows that the determination of the angular momentum barrier in open-shell atoms is nontrivial. The Stark shift is identified as the second dominant effect responsible for ionization suppression. Finally, these two effects cannot explain the Nb data. An analysis of the electron spins suggests that Pauli blocking might be responsible for the suppression of tunnelling in Nb.

Elastic partial and integral cross sections for e⁻–Fr scattering are investigated at electron energies E's near the threshold to understand the mechanism of electron attachment and predict new manifestations. The calculation uses the Mulholland formula, implemented within the complex angular momentum description of scattering wherein resonances are rigorously defined as singularities of the S-matrix. We benchmark our approach by comparing the calculated results with those from the recent Dirac R-matrix method (Bahrim et al 2001 Phys. Rev. A 63 042710). We find that near threshold there is no Ramsauer–Townsend minimum and that there is a shape resonance at E = 0.034 eV, in agreement with the Bahrim et al results. However, contrary to the Dirac R-matrix data, a new sharp f-resonance appears at E = 0.354 eV and a p-wave Wigner threshold behaviour is identified. Some results for e⁻–Cs are also presented. The general agreement with the Dirac R-matrix results gives credence to our simple and novel approach.

The photoionization cross sections of Fe V are revised in the light of recent experimental measurements. It is found that in order to calculate accurate cross sections through the close-coupling method one must account for three important effects: (1) one-electron orbitals used to represent the target ion must be optimized based on not only the target itself, but also the states of the ionizing system. This is important in order to get the right positions of 3p → 3d states with respect to the ionization threshold. (2) It is important to include the effects of coupling of 3p⁵3d^N states to the continuum; thus, the parent states 3p⁵3d^N−1 of the target have to be explicitly included in the close-coupling expansion. This is necessary for an accurate computation of resonances, but leads to very large calculations. (3) In constructing synthetic models, it is important to remove high unresolved resonances out of theoretical cross sections. Such features can be responsible for noticeable spikes or troughs that do not conform to experimental cross sections. The new theoretical cross sections agree very well with the experimental data.

In order to carry out a general analysis of the symmetry breaking effect for an atom confined to a spherical cavity, a cavity is modelled by an impenetrable wall while the interaction of an active electron with the atomic core is described by a zero-range potential. This model permits an analytical solution with the spectral equation derived as a transcendental equation that is easy to numerically analyse. Spontaneous symmetry breaking occurs for sufficiently strong attractive electron–core interactions. Namely, if in the symmetrical configuration the electron energy is negative (i.e. lies below the bottom of the cavity potential), then this configuration is unstable; the equilibrium position is shifted from the cavity centre.

This tutorial presents an extensive computational study of electron-impact scattering and ionization of atomic hydrogen and hydrogenic ions, through the solution of the non-relativistic Schrödinger equation in coordinate space using propagating exterior complex scaling (PECS). It details the complete numerical and computational development of the PECS method, which enables highly computationally-efficient solution of these collision systems. Benchmark results are presented for a complete range of electron–hydrogen collisions, including discrete elastic and inelastic scattering both below and above the ionization threshold energy, very low-energy ionizing collisions through to moderately high-energy ionizing collisions, ground-state and excited-state targets and charged hydrogenic targets with Z ⩽ 4. Total ionization cross sections through to fully differential cross sections, both in-plane and out-of-plane, are given and are found to be in excellent accord with other state-of-the-art methods and measurements, where available. We also review our recent confirmation (Bartlett and Stelbovics 2004 Phys. Rev. Lett.93 233201) of the Wannier and related threshold laws for e–H collisions.

The most accurate theoretical potentials available for the interaction of a pair of ground-state Rb atoms are used to evaluate their ultracold scattering properties. The close relation between the zero-energy scattering phase shifts and the number of bound states in the potential, by Levinson's theorem, is used to assign absolute values to the l = 0, 1 and 2 phase shifts. The number of bound states is compared with those resulting from detailed spectroscopic studies on the singlet potential and photoassociation results on the triplet potential. We review the scattering formulae needed to satisfy the Pauli principle for the fermion nuclei of ⁸⁵Rb and ⁸⁷Rb and their single unpaired electrons, for all possible initial hyperfine states. Scattering lengths are evaluated and their sensitivity to details of the asymptotic potentials is demonstrated.

We present a simple model based upon wave vector matching which gives a plausible explanation for the empirical observation that, for positron collisions with a wide variety of targets, cross sections for positronium formation are largest when the projectile kinetic energy is in the vicinity of twice the relevant threshold energy. The model is used to make predictions of cross-section trends for charge exchange processes for collisions involving a number of other positronic species.

Relativistic configuration interaction calculations have been performed for the 1s →np (n = 4–8) photoabsorption transitions in Br I and Br II, and transition energies and transition probabilities have been evaluated. These data are necessary to interpret the experiment photoabsorption spectra. The K edge energies of Br I and Br II have also been computed and compared to the existing values when available.

We describe a method for sum-frequency generation via non-degenerate four-wave mixing in classical (thermal) and quantum ultracold atomic gases (BEC). An integral part of the sum-frequency generation process is a collective instability which spontaneously generates a periodic density modulation in the atomic gas with a period comparable to the wavelength of the generated high-frequency optical field. Due to the generation of this density modulation, phase matching between the pump and generated fields is not a necessary initial condition for this sum-frequency generation process to occur: rather the density modulation acts to 'self-phase-match' the fields during the course of the sum-frequency generation process. We describe a one-dimensional model of this process, and suggest a proof-of-principle experiment to demonstrate a regime where the sum-frequency generation process evolves quantum mechanically, with discrete emission of sum-frequency photons. This experiment would involve pumping ultracold Cs atoms in a high-finesse unidirectional cavity with three infrared pump fields to produce blue light as a series of hyperbolic secant pulses.

The master equation of the quantum optical density operator is transformed to the equation of the characteristic function. Parametric amplification and amplitude damping as well as phase damping are considered. The solution for the most general initial quantum state is obtained for parametric amplification and amplitude damping. The purity of the one-mode Gaussian system and the entanglement of the two-mode Gaussian system are studied.

A tunable source of synchrotron radiation based on the interaction of a high intensity laser with small Xe clusters is studied. The synchrotron radiation yield for clusters with initial radii of 20 and 50 Å using a KrF laser (248 nm) with a pulse duration of 83.3 fs and laser intensity varying from 10¹⁷ to 10²⁰ W cm⁻² was examined theoretically. Clusters irradiated by an intense femtosecond laser pulse produce x-rays more efficiently than solids or gases, because the electrons ionized by and oscillating in the electromagnetic field of the laser absorb more energy and radiate together. This paper calculates the conversion efficiency for a ∼100 fs KrF laser pulse around 10¹⁹ W cm⁻² on Xe clusters with nm sizes to be a few percent.

We present the results of calculations of outer and next to outer shell non-dipole angular anisotropy parameters of photoelectrons for semi-filled shell atoms in the Hartree–Fock (HF) one-electron approximation and in the frame of the spin polarized random phase approximation with exchange (SP RPAE) which takes into account inter-electron correlations. We demonstrate for the first time that this characteristic of the photoionization process is essentially sensitive to whether the photoelectron has the same or opposite spin orientation to that of the semi-filled shell.

We measured the relative intensities of satellite lines in the 1s core-level photoemission spectra of Ne, as a function of excitation energy, using high-brilliant soft x-ray undulator radiation. Measured excitation functions for these satellite lines were merged with the previously reported results and discussed in terms of the intra-atomic electron–electron correlations. Some results have suggested that the internal electron scattering might play an important role in characterizing the near-threshold behaviour for the 2p →np excitation process accompanying 1s photoionization. The observed intensity ratios of the satellite lines relative to the main line were analysed with the aid of the analytic Thomas model. The observed near-threshold behaviours were also compared with the simple model calculations which take account of both the sudden creation of an inner-shell vacancy and the Coulomb interaction between the ionized electron and atomic electrons. The comparison has implied that both the amplitude and the shape of the measured excitation functions cannot be satisfactorily explained by the simple model calculations. This fact may call on an improvement in the theoretical treatment in such simple model calculations.

We present experimental results showing the diffuse reflection of a Bose–Einstein condensate from a rough mirror, consisting of a dielectric substrate supporting a blue-detuned evanescent wave. The scattering is anisotropic, more pronounced in the direction of the surface propagation of the evanescent wave. These results agree very well with theoretical predictions.

The influence of laser-induced continuum structure on the angular distribution of photoelectrons is studied in the femtosecond time domain by direct numerical solution of the time-dependent Schrödinger equation. Control of the photoelectron angular distribution is demonstrated for the hydrogen atom by coherent population transfer from the initial S-state to an excited D-state via the p-continuum and further ionization into the f-continuum states. A direct optimization procedure is used to find a domain of laser parameters, for which the efficiency of the control with respect to the time delay and energy detuning between the laser pulses is maximized.

We study the scattering of two-level atoms at narrow laser fields, modelled by a δ-shape intensity profile. The unique properties of these potentials allow us to give simple analytic solutions for one or two field zones. Several applications are studied: a single δ-laser may serve as a model for atom detection and arrival-time measurements, either by means of fluorescence or variations in occupation probabilities. We show that, in principle, this ideal detector can measure the particle density, the quantum mechanical flux, arrival-time distributions or local kinetic energy densities. Moreover, two spatially separated δ-lasers are used to investigate quantized-motion effects in Ramsey interferometry.

The adiabatic electronic molecular potentials for a HeNe(2p⁵3p) system are calculated using a model potential initially proposed by Hennecart and Masnou-Seeuws (1985 J. Phys. B. At. Mol. Phys.18 657) and later improved for internuclear distances smaller than 5.6a₀ by Bahrim et al (1997 Phys. Rev. A 56 1305). Several bonding and anti-bonding electronic states are found. The existence of several deep potential wells below 6a₀ suggests that helium and neon atoms could form a temporary molecule. The most convincing evidence for the formation of a molecular structure is the identification of modes of vibration. By solving a time-independent Schrödinger equation for the nuclear motion during a thermal collision between helium and Ne*(2p⁵3p) atoms with a Morse potential model, several modes of vibration within several electronic potential wells are identified. For the experimental testing of our predictions, a set of vibrational–electronic transitions between modes of vibration are identified and analysed. Infrared photo-absorption spectroscopy can be used to excite the modes of vibration of a HeNe(2p⁵3p) temporary molecule. The population of the neon atoms after collision and absorption of infrared photons is analysed.

We propose a simple and efficient scheme to generate a nonclassical state of a quantum system, which is composed of the one-dimension trapped-one motion and a single-cavity field mode. We also generate two-mode SU(2) Schrödinger-cat states, entangled coherent states and squeezed cat states. In addition, we show that a quantum swap gate can be implemented if the vibration mode and cavity mode are used to represent separately a qubit. The distinct feature of the scheme is that it operates in the strong-excitation regime (Ω ≫ ν), which greatly enhances operation speed.

In this paper, we study generation of entangled states in a system which consists of a single trapped ion in a cavity. We obtain a cross-Kerr-like interaction between the cavity field (photons) and the centre-of-mass motion (phonons) of the trapped ion in the Lamb–Dicke and large detuning regime. Based on this cross-Kerr-like interaction, we create hybrid entangled states between the phonon mode and the ionic internal states, and between the cavity field and ionic internal states, respectively. We also show that it is possible to prepare entangled coherent states between the cavity field and the phonon mode. We explicitly obtain an entangled state between two pairs of Schrödinger-cat states.

We study coherent backscattering of light by nonlinear scatterers in the weakly nonlinear regime. We compare full numerical calculations with a diagrammatic approach; the validity of the latter is demonstrated by the excellent agreement between these two approaches. Especially it emphasizes the fact that, in the weakly nonlinear regime, the coherent backscattering phenomenon originates, in general, from the interference between three different scattering amplitudes. This effect reveals itself in the first nonlinear correction of the backscattered intensity, which is enhanced by almost a factor three as compared to the diffuse background.

A series of R-matrix calculations on K⁺ is used to derive electron excitation and ionization cross sections. The excitation cross section to the 4s and 3d levels leading to the K⁺ 60.1, 60.8 and 61.3 nm emission lines shows a poor agreement with the cross beam experiment of Zapesochny et al (1986 Zh. Eksp. Teor. Fiz.90 1972 (Engl. Transl.: Sov. Phys.—JETP63 1155)). Cross sections are also presented for exciting the 4p, 5s and 4d levels, the autoionizing 3s open-shell levels, and for ionization. It is shown how pseudoresonances in the calculated cross section can be eliminated by increasing the target basis.

Using an extended Lewenstein model under single-active electron (SAE) and linear combination of atomic orbital approximations, we perform a theoretical investigation of the high harmonic generation (HHG) spectrum of diatomic molecular systems in intense short-pulse laser fields. The wavelet transform and Wigner distribution, two complementary time-frequency methods, are extended for the exploration of the underlying mechanisms responsible for the fine structure of HHG peaks in the plateau regime. We found that, under some conditions, the HHG fine structure is mainly due to the interference between the long and short trajectories. The extension of the cut-off in the molecular HHG spectrum is also observed when the internuclear separation is large. Detailed analysis shows that the one-centre and two-centre terms contribute, respectively, to the low- and high-energy parts of the molecular HHG spectrum.

Spin- and fine-structure resolved results for the inner-shell ionization of argon are presented. By performing measurements and relativistic scattering calculations under kinematical conditions where the contribution from the exchange between the scattered electrons and the electrons in the residual ion is small, the effect of target fine structure on the measured spin asymmetry has been highlighted. Fully relativistic distorted wave Born approximation calculations are found to be in good agreement with both the spin asymmetry and branching ratio measurements.

The closed form integral representation for the projection onto the subspace spanned by bound states of the two-body Coulomb Hamiltonian is obtained. The projection operator onto the n²-dimensional subspace corresponding to the nth eigenvalue in the Coulomb discrete spectrum is also represented as the combination of Laguerre polynomials of nth and (n − 1)th order. The latter allows us to derive an analogue of the Christoffel–Darboux summation formula for the Laguerre polynomials. The representations obtained are believed to be helpful in solving the breakup problem in a system of three charged particles where the correct treatment of infinitely many bound states in two-body subsystems is one of the most difficult technical problems.

Photoinduced Ba L x-rays were measured, in the excitation energy range of 5.6–30 keV, by using high-brilliance undulator radiation. The obtained intensity ratios, the excitation-energy independent Lβ₄/Lβ₃, Lη/Lβ₁, Lι/Lα_1,2, Lβ₆/Lα_1,2 and Lβ_2,15/Lα_1,2 as well as the excitation-energy dependent Lβ₁/Lα_1,2, Lβ₃/Lα_1,2 and Lβ₃/Lβ₁, were compared with theoretical calculations, in which the calculations were performed by applying various subsets of the L subshell fluorescence yields and Coster–Kronig yields. Deviations of the theoretical calculations from the experimental results call on improvements in theory for the emission rates. We have also surveyed the Lα_1,2 related x-ray hypersatellite lines in the photoinduced Ba L x-ray spectrum.

Production of alkali earth ions (Ca⁺, Sr⁺ and Ba⁺) by means of a laser ablation technique and measurement of their laser-induced fluorescence, cross sections of collision-induced transitions between the np ²P_J fine structure levels (n= 4, 5 and 6 for Ca⁺, Sr⁺ and Ba⁺, respectively) due to collisions with hydrogen molecules at room temperature (298 K) has been performed. The cross sections thus determined for the collisions with H₂ and D₂ are σ(Ca⁺: 4p ²P_3/2 → 4p ²P_1/2) = 20.5 ± 0.5, 27.1 ± 1.3 Ų, σ(Ca⁺: 4p ²P_1/2→ 4p ²P_3/2) = 13.2 ± 0.6, 18.7 ± 0.8 Ų, σ(Sr⁺: 5p ²P_3/2→ 5p ²P_1/2) = 22.7 ± 0.4, 18.0 ± 0.4 Ų and σ(Ba⁺: 6p ²P_3/2→ 6p ²P_1/2) = 10.4 ± 0.1, 3.4 ± 0.2 Ų, respectively.

It has come to the attention of the Institute of Physics that this article should not have been submitted for publication owing to its substantial replication of an earlier paper (Matveev V I, Matrasulov D U and Ryabchenko S V 2006 Multiple electron loss by structured heavy ions in fast collisions with complex atoms J. Exp. Theor. Phys.102 1–8, original Russian text © V I Matveev, D U Matrasulov, S V Ryabchenko 2006, published in Zh. Eksp. Teor. Fiz.129 5–13). Therefore this article has been retracted by the Institute of Physics, and by G Baur and Th Stöhlker. The JETP paper was published without the knowledge of G Baur and Th Stöhlker.