Table of contents

A simple model based on 100% quenching of metastables by threshold electrons transmitted to short distances on the polarization potential is employed. Values of the quenching rate coefficients of 1.6 × 10⁻⁶ cm³ s⁻¹ at threshold and 0.92 × 10⁻⁶ cm³ s⁻¹ at 50 K are estimated for electron collisions with metastable xenon and 1.33 × 10⁻⁶ cm³ s⁻¹ at threshold for metastable calcium.

The time evolution of atomic photoionization by an intense few-cycle laser pulse is theoretically investigated. A possible modification of the recent attosecond tunnelling experiment in Uiberacker et al (2007 Nature446 627) is proposed, which consists of measuring the yield of the doubly charged Li ions produced by the combined action of a strong few-cycle infrared pulse and an ultrashort (attosecond) extreme ultraviolet (XUV) pulse. We predict the results of such an experiment, based on the numerical solution of the time-dependent Schrödinger equation, which describes the atomic electron in a strong laser field. The influence of the XUV pulse is treated in the sudden approximation. It is shown that the dependence of the double ionization cross section on the time delay between the two pulses reflects the time evolution of the strong-field ionization. We demonstrate that even more detailed information can be gained from the forward–backward asymmetry of the photoelectron emission.

We present a method of transferring a cold atom between spatially separated microtraps by means of a Raman transition between the ground motional states of the two traps. The intermediate states for the Raman transition are the vibrational levels of a third microtrap, and we determine the experimental conditions for which the overlap of the wavefunctions leads to an efficient transfer. There is a close analogy with the Franck–Condon principle in the spectroscopy of molecules. The spin-dependent manipulation of neutral atoms in microtraps has important applications in quantum information processing. We also show that, starting with several atoms, precisely one atom can be transferred to the final potential well hence giving deterministic preparation of single atoms.

Some E1 transitions in the francium isoelectronic sequence are computed in the 'Dirac–Fock + core-polarization' approximation, where core–valence electron correlation is treated in a semiclassical core-polarization picture. The obtained ionization energies and oscillator strengths are tested versus very accurate many-body perturbation treatment (MBPT) theoretical results published recently as well as versus available experimental data. The role of core–valence correlation (core polarization) is carefully studied for both ionization energies and oscillator strengths along the spectral series and isoelectronic sequence. Profound anomalies in oscillator strength fine structure components for the principal series of neutral francium are predicted and await experimental confirmation.

We study fully differential cross sections (FDCS) for single ionization of helium by ion impact in the presence of a laser field. The field is assumed to have linear polarization, to be weak compared to the typical atomic field, and we use a frequency corresponding to a CO₂ laser. We employ the continuum distorted wave-eikonal initial state (CDW-EIS) to describe our FDCS in the laser background. Analysing our numerical results we explore the dependence of the FDCS on the laser field properties as well as on the ionized electron parameters.

We investigate resonant strong field ionization of atomic hydrogen with respect to the 1s–2p transition. By 'strong' we understand that Rabi periods are executed on a femtosecond time scale. Ionization and AC Stark shifts modify the bound state dynamics severely, leading to nonperturbative signatures in the photoelectron spectra. We introduce an analytical model, capable of predicting qualitative features in the photoelectron spectra such as the positions of the Autler–Townes peaks for modest field strengths. Ab initio solutions of the time-dependent Schrödinger equation show a pronounced shift and broadening of the left Autler–Townes peak as the field strength is increased. The right peak remains rather narrow and shifts less. This result is analysed and explained with the help of exact AC Stark shifts and ionization rates obtained from Floquet theory. Finally, it is demonstrated that in the case of finite pulses as short as 20 fs the Autler–Townes duplet can still be resolved. The fourth generation light sources under construction worldwide will provide bright, coherent radiation with photon energies ranging from a tenth of an meV up to tens of keV, hence covering the regime studied in the paper so that measurements of nonperturbative, relative AC Stark shifts should become feasible with these new light sources.

The bound-state properties and hyperfine structure splitting in the ground -states of the three-electron beryllium-muonic atoms ⁹Be⁴⁺μ⁻e⁻₃ and ¹⁰Be⁴⁺μ⁻e⁻₃ are determined numerically with the use of highly accurate variational five-body wavefunctions. All computations of the beryllium-muonic atoms are performed with the use of the two independent electron spin functions.

The two-electron radial D₂(r₁, r₂) and angular A₂(Ω₁, Ω₂) density functions are the probability densities that one electron is located at a radius r₁ and another at r₂ and that one electron is located along a direction Ω₁ = (θ₁, ϕ₁) and another along Ω₂ = (θ₂, ϕ₂), respectively, when any two electrons are considered simultaneously. Within the Hartree–Fock framework, these densities are the sums of contributions D^ij₂(r₁, r₂) and A^ij₂(Ω₁, Ω₂) from a pair of spin orbitals i and j. Theoretical analyses of the contributions D^ij₂(r₁, r₂) and A^ij₂(Ω₁, Ω₂) for atoms show that there exist an 'electron–electron radial hole' D^ij₂(r, r) = 0 and an 'electron–electron angular hole' A^ij₂(Ω, ± Ω) = 0 for a pair of spin orbitals with particular conditions. The radial and angular holes add new holes to the electron–electron coalescence (or Fermi) hole for two spin orbitals with the same spin and the electron–electron counterbalance hole for two spin orbitals with the same spin and the same spatial inversion symmetry.

We propose a two-colour scheme of atom guide and 1D optical lattice using evanescent light fields of TE₀₀ and TE₀₁ transverse modes in an optical waveguide. The optical waveguide carries red-detuned light and blue-detuned light, with both modes far from resonance. The atom guide and 1D optical lattice potentials can be transformed to each other by using a Mach–Zehnder interferometer to accurately control mode transformation. This might provide a new approach to realize flexible transition between the guiding and trapping states of atoms.

Collisional broadening and shift data for even parity states of neutral barium are presented. A two-photon absorption technique is used to populate Rydberg states of nd ¹D₂, ³D₂ and ¹S₀ series. High-resolution Ba excitation spectra were measured using a diode detector while scanning the frequency of an excimer pumped dye laser. Inert gases Ar, Kr and Xe were used as perturbers at pressures ranging from 10 mb to 400 mb. Shifts and broadenings of spectral lines were measured as a function of pressure and principal quantum number n. Several perturbations and deviations from expected results are discussed in this paper.

In this paper, we investigate the collapse-revival phenomenon and the Poissonian statistics of a four-level N-configuration atom interacting with two-mode cavity fields. We assume that the transition between the upper level and the third level of an atom is coupled by the frequency of mode one, while the other transitions are coupled by the frequencies of the two modes or mode two. The interaction is a multi-photon process and a Kerr medium is taken into account in the non-resonant case. We solve the models when the atom is initially prepared in a coherent superposition of the upper and ground states and the field is considered in a coherent state. The effects of both the detuning and the Kerr medium on the temporal behaviour of some statistical aspects are analysed. The conclusions are reached and some features are given.

We investigate the nonlinearity-assisted quantum tunnelling and formation of nonlinear collective excitations in a matter-wave interferometer, which is realized by the adiabatic transformation of a double-well potential into a single-well harmonic trap. In contrast to the linear quantum tunnelling induced by the crossing (or avoided crossing) of neighbouring energy levels, the quantum tunnelling between different nonlinear eigenstates is assisted by the nonlinear mean-field interaction. When the barrier between the wells decreases, the mean-field interaction aids quantum tunnelling between the ground and excited nonlinear eigenstates. The resulting non-adiabatic evolution depends on the input states. The tunnelling process leads to the generation of dark solitons, and the number of the generated dark solitons is highly sensitive to the matter-wave nonlinearity. The results of the numerical simulations of the matter-wave dynamics are successfully interpreted with a coupled-mode theory for multiple nonlinear eigenstates.

This is the first in a series of articles in which we study the rotating Morse potential model for diatomic molecules in the tridiagonal J-matrix representation. Here, we compute the bound-state energy spectrum by diagonalizing the finite-dimensional Hamiltonian matrix of H₂, LiH, HCl and CO molecules for arbitrary angular momentum. The calculation was performed using the J-matrix basis that supports a tridiagonal matrix representation for the reference Hamiltonian. Our results for these diatomic molecules have been compared with available numerical data satisfactorily. The proposed method is handy, very efficient, and it enhances accuracy by combining analytic power with a convergent and stable numerical technique.

Based on the semiclassical impact parameter method, a theoretical model is constructed to calculate fully differential cross sections for single ionization of helium by impact with fast C⁶⁺ ions. A good agreement with the experiment is achieved in the scattering plane, while in the perpendicular plane a structure similar to that observed experimentally is obtained. The contribution of different partial waves to the cross section is also investigated.

Ab initio calculation of the total dielectronic recombination (DR) rate coefficient from the ground and the first excited states of Co-like gold is performed employing the relativistic distorted-wave approximation with configuration interaction. The DR contributions are explicitly taken into account from the relevant complexes of a Ni-like ion: 3d³_3/2 3d⁶_5/2n'l', 3p⁵ 3d¹⁰n'l', 3s 3p⁶3d¹⁰n'l', 3d⁸ 4ln'l', 3p⁵ 3d⁹ 4ln'l' and 3s 3p⁶ 3d⁹ 4ln'l' with n' ⩽ 25, and 3d⁸ 5ln'l' with n' ⩽ 9. The contributions from a higher n' complex are evaluated by an extrapolation procedure. The DR contributions mainly come from complex series 3d⁸ 4ln'l' and 3p⁵ 3d⁹ 4ln'l'. The complex series 3p⁵ 3d¹⁰n'l' and 3d⁸ 5ln'l' also contribute significantly to the total DR rates at low and high electron temperatures, respectively. The l' and n' dependences of the partial rate coefficient are investigated. The possible important decays into autoionizing levels followed by radiative cascade (DAC) from the resonant levels are taken into account, as well as the resonant stabilizing and non-resonant stabilizing transitions. The inclusion of DAC transitions enlarges the total DR rate coefficients by a factor of about 10% and may break down the usual n'⁻³ scaling law of the partial DR rates along some complex series. To evaluate the high n' contributions from these complex series, the level-by-level extrapolation method is developed to include DAC effects. The total DR rate coefficients are fitted to an empirical formula. The present results are compared with those from the semiempirical Burgess–Merts approximation. The DR rate coefficients of Ni-like gold are also presented and compared to those of Co-like gold. In addition, some comments on the published DR data for the NiI isoelectronic sequence are drawn from the present calculation.

The light propagation of a probe field in a three-level Λ system with incoherent pumping has been studied when both dynamically induced coherence (DIC) and spontaneously generated coherence (SGC) play a significant role. We have investigated the group velocity of probe field and hence the group index of a three-level Λ system with incoherent pumping when both DIC and SGC play a significant role. We have shown that by varying the probe field Rabi frequency one can control the interference between these two coherences which leads to different nonlinear response (amplification without inversion, electromagnetically induced transparency and electromagnetically induced absorption) leading to different (positive and negative) dispersion. Hence control over switching of group velocity from subluminal to superluminal and vice versa can be achieved. We have also shown that when the contributions from both the coherences are comparable, the dependence of group velocity of probe field in a three-level Λ system with incoherent pumping on phase difference between probe and coherent fields is different from that obtained under the weak probe field condition. Going beyond the weak probe field approximation we have derived analytical expressions for group velocity and hence the group index in the steady state limit (keeping all orders of system parameters) to generalize the analysis, and these expressions can be used for any set of system parameters without any restriction. The numerical values obtained by solving the density matrix equations agree well with these exact analytical values at a large time limit. We have proposed a scheme for experimental realization of EIT and hence subluminal light propagation in molecules by invoking spontaneously generated coherence.