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Accurate photodissociation cross sections have been computed for transitions from the X $^1\Sigma^+$ ground electronic state of CS to six low-lying excited electronic states. New ab initio potential curves and transition dipole moment functions have been obtained for these computations using the multi-reference configuration interaction approach with the Davidson correction (MRCI+Q) and aug-cc-pV6Z basis sets. State-resolved cross sections have been computed for transitions from nearly the full range of rovibrational levels of the X $^1\Sigma^+$ state and for photon wavelengths ranging from 500 $\text{\AA}$ to threshold. Destruction of CS via predissociation in highly excited electronic states originating from the rovibrational ground state is found to be unimportant. Photodissociation cross sections are presented for temperatures in the range between 1000 and 10,000 K, where a Boltzmann distribution of initial rovibrational levels is assumed. Applications of the current computations to various astrophysical environments are briefly discussed focusing on photodissociation rates due to the standard interstellar and blackbody radiation fields., Comment: 16 pages, 9 figures, 4 tables

The capability of intense ultrashort laser pulses to initiate, control and image vibrational wavepacket dynamics in the deuterium molecular ion has been simulated with a view to inform and direct future femtosecond pump–control–probe experiments. The intense-field coherent control of the vibrational superposition has been studied as a function of pulse intensity and delay time, to provide an indication of key constraints for experimental studies. For selected cases of the control mechanism, probing of the subsequent vibrational wavepacket dynamics has been simulated via the photodissociation (PD) channel. Such PD probing is shown to elucidate the modified wavepacket dynamics where the position of the quantum revival is sensitive to the control process. Through Fourier transform analysis the PD yield is also shown to provide a characterisation of the vibrational distribution. It has been shown that a simple ‘critical R cut-off’ approximation can be used to reproduce the effect of a probe pulse interaction,...

The dynamics of dissociation of pre-ionized D+2 molecules using intense (1012–1015 W cm−2), ultrashort (50 fs), infrared (λ = 790 nm) laser pulses are examined. Use of an intensity selective scan technique has allowed the deuterium energy spectrum to be measured over a broad range of intensity. It is found that the dominant emission shifts to lower energies as intensity is increased, in good agreement with corresponding wavepacket simulations. The results are consistent with an interpretation in terms of bond softening, which at high intensity (approximately >3 × 1014 W cm−2) becomes dominated by dissociative ionization. Angular distribution measurements reveal the presence of slow molecular dissociation, an indication that vibrational trapping mechanisms occur in this molecule.

A novel technique is proposed to control the dissociation mechanism of small diatomic molecules. This technique, relying upon the creation of a coherent nuclear wavepacket, uses intense (>1014 W cm−2), ultrashort (~10 fs) infrared laser pulses in a pump and probe scheme. In applying this technique to D+2 good agreement has been observed between a quantum simulation and experiment. This represents a major step towards quantum state control in molecules, using optical fields.

Few-cycle laser pulses are used to “pump and probe” image the vibrational wavepacket dynamics of a HD+ molecular ion. The quantum dephasing and revival structure of the wavepacket are mapped experimentally with time-resolved photodissociation imaging. The motion of the molecule is simulated using a quantum-mechanical model predicting the observed structure. The coherence of the wavepacket is controlled by varying the duration of the intense laser pulses. By means of a Fourier transform analysis both the periodicity and relative population of the vibrational states of the excited molecular ion have been characterized.

A realistic model of the dipole radiation forces in transverse Doppler cooling (with a σ+–σ− laser configuration) of an atomic beam of group 13 elements is studied within the quantum-kinetic equation framework. The full energy level sub-structure for such an atom with I = 0 (such as 66Ga) is analysed. Two cooling strategies are investigated; the first involving the 2P3/2 → 2D5/2 transition and the second a dual laser cooling experiment involving transitions 2P1/2 and 2P3/2 → 2S1/2. The latter scheme creates a velocity-independent dark-state resonance that inhibits a steady-state dipole cooling force. However, time-dependent calculations show that transient cooling forces are present that could be exploited for laser cooling purposes in pulsed laser fields.

The vibrational wavepacket revival of a basic quantum system is demonstrated experimentally. Using few-cycle laser pulse technology, pump and probe imaging of the vibrational motion of D+2 molecules is conducted, and together with a quantum-mechanical simulation of the excited wavepacket motion, the vibrational revival phenomenon has been characterised. The simulation shows good correlation with the temporal motion and structural features obtained from the data, relaying fundamental information on this diatomic system.

We discuss the properties of the lifetime or the time-delay matrix Q(E) for multichannel scattering, which is related to the scattering matrix S(E) by Q = iS(dS†/dE). For two overlapping resonances occurring at energies Eν with widths Γν(ν = 1, 2), with an energy-independent background, only two eigenvalues of Q(E) are proved to be different from zero and to show typical avoided-crossing behaviour. These eigenvalues are expressible in terms of the four resonance parameters (Eν, Γν) and a parameter representing the strength of the interaction of the resonances. An example of the strong and weak interaction in an overlapping double resonance is presented for the positronium negative ion. When more than two resonances overlap (ν = 1, ..., N), no simple representation of each eigenvalue has been found. However, the formula for the trace of the Q-matrix leads to the expression δ(E) = −∑arctan[(Γν/2)/(E − Eν)] + δb(E) for the eigenphase sum δ(E) and the background eigenphase sum δb(E), in agreement with the known form of the state density. The formulae presented in this paper are useful in a parameter fitting of overlapping resonances.

We review recent work carried out in Belfast which handles the few-electron dynamics of atomic and molecular systems exposed to high frequency, high intensity laser fields. The design and application of the quantitatively accurate computational methods is discussed. The Belfast work is illustrated by results for double ionization of helium and the hydrogen molecule by FEL XUV light where in each case the two electrons have been handled in full-dimensionality.

Accurate and efficient grid based techniques for the solution of the time-dependent Schrodinger equation for few-electron diatomic molecules irradiated by intense, ultrashort laser pulses are described. These are based on hybrid finite-difference, Lagrange mesh techniques. The methods are applied in three scenarios, namely H2 + with fixed internuclear separation, H2 + with vibrating nuclei and H2 with fixed internuclear separation and illustrative results presented.

We review work carried out in recent years at Belfast devoted to handling the dynamics of laser-driven few-electron atomic and molecular systems in full dimensionality with the goal of bringing quantitative discipline to the field. The design and application of quantitatively accurate computational methods are discussed. Electron-electron correlations induced by intense external fields are observed by calculating the position and momentum space distributions of the doubly ionizing two-electron wave packets and the application of the techniques of scientific visualization analysis to such studies is emphasized. Agreement of results obtained with those from recent laboratory experiments is demonstrated. Work in hand and plans for future calculations are outlined.

Above a critical velocity, the dominant mechanism of energy transfer between a moving object and a dilute Bose-Einstein condensate is vortex formation. In this paper, we discuss the critical velocity for vortex formation and the link between vortex shedding and drag in both homogeneous and inhomogeneous condensates. We find that at supersonic velocities sound radiation also contributes significantly to the drag force., 10 pages, 5 figures. submitted to J. Phys. B for the special issue on Coherent Matter Waves

We present the Floquet method of calculation of multiphoton ionization rates from the dressed σ g + and σ u + states of H 2 + . Our software allows a determination of ionization rates for a range of laser frequencies, intensities and internuclear separations. The theoretical method is discussed and instructions for use of the accompanying computer program, which also produces ionization rates for DC field ionization, are given.

We solve the Gross-Pitaevskii equation to model the behaviour of a weakly-interacting Bose condensate. Solutions are presented for the eigenstates in one- and two-dimensional harmonic traps. We include the effect of gravity and coupling to a second condensate to simulate an output coupler for Bose condensed atoms, and find that the output pulse shape is in qualitative agreement with experiment. We also model flow under gravity through a constriction, demonstrating excitation and separation of eigenmodes in the condensate., 10 pages, 6 figures, REVTeX. Revised version, to appear in J. Phys. B

We solve the time-dependent Gross-Pitaevskii in 2D to simulate the flow of an object through a dilute Bose-Einstein condensate trapped in a harmonic well. We demonstrate vortex formation and study the process in terms of the accumulation of phase slip and the evolution of the fluid velocity.

Ultracold hybrid ion-atom traps offer the possibility of microscopic manipulation of quantum coherences in the gas using the ion as a probe. However, inelastic processes, particularly charge transfer can be a significant process of ion loss and has been measured experimentally for the Yb$^{+}$ ion immersed in a Rb vapour. We use first-principles quantum chemistry codes to obtain the potential energy curves and dipole moments for the lowest-lying energy states of this complex. Calculations for the radiative decay processes cross sections and rate coefficients are presented for the total decay processes. Comparing the semi-classical Langevin approximation with the quantum approach, we find it provides a very good estimate of the background at higher energies. The results demonstrate that radiative decay mechanisms are important over the energy and temperature region considered. In fact, the Langevin process of ion-atom collisions dominates cold ion-atom collisions. For spin dependent processes \cite{kohl13} the anisotropic magnetic dipole-dipole interaction and the second-order spin-orbit coupling can play important roles, inducing couplingbetween the spin and the orbital motion. They measured the spin-relaxing collision rate to be approximately 5 orders of magnitude higher than the charge-exchange collision rate \cite{kohl13}. Regarding the measured radiative charge transfer collision rate, we find that our calculation is in very good agreement with experiment and with previous calculations. Nonetheless, we find no broad resonances features that might underly a strong isotope effect. In conclusion, we find, in agreement with previous theory that the isotope anomaly observed in experiment remains an open question., Comment: 7 figures, 1 table accepted for publication in J. Phys. B: At. Mol. Opt. Phys. arXiv admin note: text overlap with arXiv:1107.1141

We present calculations of quasienergies of the lower states of the hydrogen molecular ion in a strong external electric field. Arbitrary orientations of the molecular axis are considered for the first time. We study the variation of ionization rate with internuclear separation. This work is relevant to the angular and energy distributions of dissociative ionization fragments. The ionization rates of the lowest states are, in general, very sensitive to orientation: for certain orientations the excited state is more stable than the ground state. The rates for the excited states rise very sharply as the field increases. For very intense fields ionization arises predominantly from small internuclear distances rather than large critical bond lengths. For low-frequency intense laser fields this would imply that the critical region for nonclassical Coulomb explosions occurs very close to the neutral bonding distance. The dipole moment is found to be easily decoupled from the molecular axis for these field strengths giving rise to a broad angular distribution of photofragments. Comparisons with recent complementary calculations for a parallel orientation confirm the accuracy of our results.

We calculate the quasienergies and wavefunctions of the hydrogen molecular ion perturbed by a strong external electric field. Results are obtained for static-field ionization rates of the lowest dressed states. The nonlinear Stark shifts are also calculated for weak and strong fields for a range of internuclear separations. Charge and current densities are obtained and used to explain the ionization resonance structure. The ionization currents are found to be very sensitive to field strength and internuclear distance. There is evidence of critical distances that indicate the validity of Coulomb explosion models and electron localization. However, for this system, the results do not agree well with simple over-barrier models of electron release. Multiphoton ionization rates of low-frequency intense laser fields are estimated by cycle averaging.

We use the complex-basis-function technique to calculate one- and two-photon photoionization rates in intense light sources for atomic hydrogen, the hydrogen negative ion and the hydrogen molecular ion. For H2+ we also calculate three-photon ionization rates. Rather than calculating the ionization rates in the perturbation approximation, we take account of strong field effects by calculating complex quasienergies using a mixture of real and complex-basis functions. This allows us to extend the calculations from the perturbative to the non-perturbative regime as the laser intensity is increased. The method works well and gives reliable estimates of these rates.

In order to study ultracold charge-transfer processes in hybrid atom-ion traps, we have mapped out the potential energy curves and molecular parameters for several low lying states of the Rb, Yb$^+$ system. We employ both a multi-reference configuration interaction (MRCI) and a full configuration interaction (FCI) approach. Turning points, crossing points, potential minima and spectroscopic molecular constants are obtained for the lowest five molecular states. Long-range parameters, including the dispersion coefficients are estimated from our {\it ab initio} data. The separated-atom ionization potentials and atomic polarizability of the ytterbium atom ($\alpha_d=128.4$ atomic units) are in good agreement with experiment and previous calculations. We present some dynamical calculations for (adiabatic) scattering lengths for the two lowest (Yb,Rb$^+$) channels that were carried out in our work. However, we find that the pseudo potential approximation is rather limited in validity, and only applies to nK temperatures. The adiabatic scattering lengths for both the triplet and singlet channels indicate that both are large and negative in the FCI approximation., Comment: 8 pages, 3 figures, 5 tables

This paper derives a general procedure for the numerical solution of the Lindblad equations that govern the coherences arising from multicoloured light interacting with a multilevel system. A systematic approach to finding the conservative and dissipative terms is derived and applied to the laser cooling of gallium. An improved numerical method is developed to solve the time-dependent master equation and results are presented for transient cooling processes. The method is significantly more robust, efficient and accurate than the standard method and can be applied to a broad range of atomic and molecular systems. Radiation pressure forces and the formation of dynamic dark-states are studied in the gallium isotope 66Ga., Comment: 15 pages, 8 figures

Recent experiments have demonstrated how quantum-mechanical impurities can be created within strongly correlated quantum gases and used to probe the coherence properties of these systems [S. Palzer, C. Zipkes, C. Sias, and M. K\"ohl, Phys. Rev. Lett. 103, 150601 (2009).]. Here we present a phenomenological model to simulate such an output coupler for a Tonks-Girardeau gas that shows qualitative agreement with the experimental results for atom transport and output coupling. Our model allows us to explore nonequilibrium transport phenomena in ultracold quantum gases and leads us to predict a regime of atom blockade, where the impurity component becomes localized in the parent cloud despite the presence of gravity. We show that this provides a stable mixed-species quantum gas in the strongly correlated limit.

The dressed-molecule method is employed to simulate the interference of two- and four- (2+4) photon transitions between the ground XΣ+g and the excited predissociated 2Πg state of Cl2. By variation of the relative phase and intensity of two lasers (one of frequency ω4, the other of frequency ω2=2ω4) it is shown that predissociation in the Πg state can be suppressed selectively, i.e. one vibrational level at a time. Consequently, it is possible to control the dissociation yield from the Πg predissociation channel.

The formation of ground-state positronium in collisions of positrons with hydrogen and helium atoms is considered within the distorted-wave Born approximation. In particular the authors analyse the eikonal and continuum-distorted-wave models in both their post and prior forms. Differential and total cross sections are calculated over a broad range of intermediate energies extending from 40 to 500 eV. The results confirm that the total cross section decreases rapidly with increasing energy, as predicted by the simple first Born approximation, and do not agree with experimental evidence of a slower decay. The computed total cross sections for helium targets agree with those of the close-coupling model for energies above 100 eV. Below 100 eV the authors find a large post-prior discrepancy. The calculated differential cross sections show evidence of a Thomas peak at high energies for the CDW models but not for the eikonal models.

The author presents exact calculations of the distorted-wave impulse approximation for electron capture by fast protons from hydrogen and by lithium ions from neon. Results for total and differential cross sections are presented, and comparison is made with other models of electron capture as well as experimental measurements. A detailed derivation of the impulse approximation is presented within the framework of the distorted-wave approximation, and its relation to the strong-potential Born approximation is clarified. It is indicated that the approximations involved in the impulse approximation are less severe than those of the Born approximation for simple rearrangement collisions. The validity of certain peaking approximations is analysed. The implications for highly asymmetric and nearly symmetric charge transfer collisions are briefly discussed.

The states of a boson pair in a one-dimensional double-well potential are investigated. Properties of the ground and lowest excited states of this system are studied, including the two-particle wavefunction, momentum pair distribution and entanglement. The effects of varying both the barrier height and the effective interaction strength are investigated., Comment: 16 pages, 15 figures

We present a new algorithm for vibrational control in deuterium molecules that is feasible with current experimental technology. A pump mechanism is used to create a coherent superposition of the D2+ vibrations. A short, intense infrared control pulse is applied after a chosen delay time to create selective interferences. A `chessboard' pattern of states can be realized in which a set of even- or odd-numbered vibrational states can be selectively annihilated or enhanced. A technique is proposed for experimental realization and observation of this effect using 5 fs pulses of 790 nm radiation, with intermediate intensity (5e13 W/cm2), Comment: 12 pages, 5 figures

The Zakharov-Shabat equations are solved using the semiclassical phase-integral formalism. The results are discussed in relation to the creation of soliton pulses of a phase-modulated optical pulse in an optical fibre or two-level medium. Following the method of Crothers and Stueckelberg, the quantisation of a complex phase-integral of an adiabatic action is proposed as a criterion for the existence of such solutions. The formula is found to accord with the class of exact solutions of Kunicke's model. A formula is also proposed for a simple phase-modulated step pulse.

Two-step photodissociation angular distributions are calculated by a coupled-equation approach for the 1 $^{1}\mathrm{\ensuremath{\Sigma}}_{\mathit{g}}^{+}$\ensuremath{\rightarrow}1 $^{1}\mathrm{\ensuremath{\Pi}}_{\mathit{u}}$\ensuremath{\rightarrow}1 $^{1}\mathrm{\ensuremath{\Pi}}_{\mathit{g}}$ transition in $^{7}\mathrm{Li}_{2}$. The initial excitation is induced by a low-intensity visible laser in order to select the rovibrational state. The \ensuremath{\Pi}-\ensuremath{\Pi} transition is effected by an infrared laser that is varied from weak (perturbative) to intense (nonperturbative) regimes. It is shown that laser-induced orientation effects and laser-induced resonances (trapped states) considerably alter the angular distribution of the photodissociating fragments, creating anomalies in some instances at high intensities where a nonperturbative, numerical approach is essential.

Tunnel ionization of room-temperature ${\mathrm{D}}_{2}$ in an ultrashort (12 femtosecond) near infrared $(800\phantom{\rule{0.3em}{0ex}}\mathrm{nm})$ pump laser pulse excites a vibrational wavepacket in the ${{\mathrm{D}}_{2}}^{+}$ ions; a rotational wavepacket is also excited in residual ${\mathrm{D}}_{2}$ molecules. Both wavepacket types are collapsed a variable time later by an ultrashort probe pulse. We isolate the vibrational wavepacket and quantify its evolution dynamics through theoretical comparison. Requirements for quantum computation (initial coherence and quantum state retrieval) are studied using this well-defined (small number of initial states at room temperature, initial wavepacket spatially localized) single-electron molecular prototype by temporally stretching the pump and probe pulses.

We present a simple quantum mechanical model to describe Coulomb explosion of H{sub 2}{sup +} and D{sub 2}{sup +} by short, intense infrared laser pulses. The model is based on the length gauge version of the molecular strong-field approximation and is valid when the process of dissociation prior to ionization is negligible. The results are compared with recent experimental data for the proton kinetic energy spectrum [Th. Ergler et al., Phys. Rev. Lett. 95, 093001 (2005); D. S. Murphy et al., J. Phys. B 40, S359 (2007)]. Using a Franck-Condon distribution over initial vibrational states, the theory reproduces the overall shape of the spectrum with only a small overestimation of slow protons. The agreement between theory and experiment can be made perfect by using a non-Frank-Condon initial distribution characteristic for H{sub 2}{sup +} (D{sub 2}{sup +}) targets produced by strong-field ionization of H{sub 2} (D{sub 2}). For comparison, we also present results obtained by two different tunneling models for this process.

Intense, few-femtosecond pulse technology has enabled studies of the fastest vibrational relaxation processes. The hydrogen group vibrations can be imaged and manipulated using intense infrared pulses. Through numerical simulation, we demonstrate an example of ultrafast coherent control that could be effected with current experimental facilities, and observed using high-resolution time-of-flight spectroscopy. The proposal is a pump-probe-type technique to manipulate the D2+ ion with ultrashort pulse sequences. The simulations presented show that vibrational selection can be achieved through pulse delay. We find that the vibrational system can be purified to a two-level system thus realizing a vibrational qubit. A novel scheme for the selective transfer of population between these two levels, based on a Raman process and conditioned upon the delay time of a second control-pulse is outlined, and may enable quantum encoding with this system.

We describe the properties of a pair of ultracold bosonic atoms in a one-dimensional harmonic trapping potential with a tunable zero-ranged barrier at the trap centre. The full characterisation of the ground state is done by calculating the reduced single-particle density, the momentum distribution and the two-particle entanglement. We derive several analytical expressions in the limit of infinite repulsion (Tonks-Girardeau limit) and extend the treatment to finite interparticle interactions by numerical solution. As pair interactions in double wells form a fundamental building block for many-body systems in periodic potentials, our results have implications for a wide range of problems., 9 pages, 8 figures

Radiative decay processes at cold and ultra cold temperatures for sulfur atoms colliding with protons are investigated. The MOLPRO quantum chemistry suite of codes was used to obtain accurate potential energies and transition dipole moments, as a function of internuclear distance, between low-lying states of the SH+ molecular cation. A multi-reference configuration-interaction approximation together with the Davidson correction is used to determine the potential energy curves and transition dipole moments, between the states of interest, where the molecular orbitals are obtained from state-averaged multi-configuration-self-consistent field calculations. The collision problem is solved approximately using an optical potential method to obtain radiative loss, and a fully two-channel quantum approach for radiative charge transfer. Cross sections and rate coefficients are determined for the first time for temperatures ranging from 10 μK up to 10 000 K. Results are obtained for all isotopes of sulfur, colliding with H+ and D+ ions and comparison is made to a number of other collision systems.

The ionization dynamics of ${{\mathrm{H}}_{2}}^{+}$ exposed to high-intensity, high-frequency, ultrashort laser pulses is investigated with two theoretical approaches. The time-dependent Schr\"odinger equation is solved by a direct numerical method, and a simple two-center interference-diffraction model is studied. The energy and angular distributions of the photoelectron for various internuclear distances and relative orientations between the internuclear axis of the molecule and the polarization of the field are calculated. The main features of the photoelectron spectrum pattern are described well by the interference-diffraction model, and excellent quantitative agreement between the two methods is found. The effect of quantal vibration on the photoelectron spectrum is also calculated. We find that vibrational average produces some broadening of the main features, but that the patterns remain clearly distinguishable.

Mode-mixing of coherent excitations of a trapped Bose-Einstein condensate is modelled using the Bogoliubov approximation. Hybridization of the modes of the breather ($l=0$) and surface ($l=4$) states leads to the formation of a Bogoliubov dark state. Calculations are presented for second-harmonic generation between the two lowest-lying even-parity $m=0$ modes in an oblate spheroidal trap. Two hybrid modes are strongly excited near second-harmonic resonance, and the coupling strength, and hence conversion rate, to the breather mode is half that given by an equivalent hydrodynamic estimate., 4 pages, 4 figures

The dynamics of toroidal condensates in the presence of condensate flow and dipole perturbation have been investigated. The Bogoliubov spectrum of condensate is calculated for an oblate torus using a discrete-variable representation and a spectral method to high accuracy. The transition from spheroidal to toroidal geometry of the trap displaces the energy levels into narrow bands. The lowest-order acoustic modes are quantized with the dispersion relation $\omega \sim |m| \omega_s $ with $m=0,\pm 1,\pm 2, ...$. A condensate with toroidal current $\kappa$ splits the $|m|$ co-rotating and counter-rotating pair by the amount: $\Delta E \approx 2 |m|\hbar^2 \kappa < r^{-2}>$. Radial dipole excitations are the lowest energy dissipation modes. For highly occupied condensates the nonlinearity creates an asymmetric mix of dipole circulation and nonlinear shifts in the spectrum of excitations so that the center of mass circulates around the axis of symmetry of the trap. We outline an experimental method to study these excitations., Comment: 8 pages, 8 figures

The gyroscopic motion of a trapped Bose gas containing a vortex is studied. We model the system as a classical top, as a superposition of coherent hydrodynamic states, by solution of the Bogoliubov equations, and by integration of the time-dependent Gross-Pitaevskii equation. The frequency spectrum of Bogoliubov excitations, including quantum frequency shifts, is calculated and the quantal precession frequency is found to be consistent with experimental results, though a small discrepancy exists. The superfluid precession is found to be well described by the classical and hydrodynamic models. However the frequency shifts and helical oscillations associated with vortex bending and twisting require a quantal treatment. In gyroscopic precession, the vortex excitation modes $m=\pm 1$ are the dominant features giving a vortex kink or bend, while the $m=+2$ is found to be the dominant Kelvin wave associated with vortex twisting., 18 pages, 7 figures, 1 table

A time-dependent method for calculating the collective excitation frequencies and densities of a trapped, inhomogeneous Bose-Einstein condensate with circulation is presented. The results are compared with time-independent solutions of the Bogoliubov-deGennes equations. The method is based on time-dependent linear-response theory combined with spectral analysis of moments of the excitation modes of interest. The technique is straightforward to apply, is extremely efficient in our implementation with parallel FFT methods, and produces highly accurate results. The method is suitable for general trap geometries, condensate flows and condensates permeated with vortex structures., 6 pages, 3 figures small typos fixed

Capture of slow antiprotons by atomic hydrogen and positronium is simulated by the classical trajectory Monte Carlo method. Statistically accurate cross sections for protonium and antihydrogen formation are obtained and the energy dependence of the process is established. The results agree very well with experimental data for proton capture by positronium. Antihydrogen formation from antiproton-positronium collisions in the presence of a laser is simulated and the effects of laser polarization, frequency, and intensity are studied. Enhancements of the antihydrogen formation cross section are observed. For example, an increase of 70% is found for light of intensity $1.4\ifmmode\times\else\texttimes\fi{}{10}^{13} {\mathrm{W}\mathrm{}\mathrm{}\mathrm{cm}}^{\ensuremath{-}2}$ and wavelength $\ensuremath{\lambda}=248 \mathrm{nm},$ for an antiproton collision energy of 1 keV.

We solve the Gross-Pitaevskii equation to study energy transfer from an oscillating `object' to a trapped Bose-Einstein condensate. Two regimes are found: for object velocities below a critical value, energy is transferred by excitation of phonons at the motion extrema; while above the critical velocity, energy transfer is via vortex formation. The second regime corresponds to significantly enhanced heating, in agreement with a recent experiment., 4 pages, 5 figures, RevTeX. Typo corrected and Figure 5 modified to include more data. Accepted for publication in Phys. Rev. A

Vortex dynamics in inhomogeneous Bose-Einstein condensates are studied numerically in two and three dimensions. We simulate the precession of a single vortex around the center of a trapped condensate, and use the Magnus force to estimate the precession frequency. Vortex ring dynamics in a spherical trap are also simulated, and we discover that a ring undergoes oscillatory motion around a circle of maximum energy. The position of this locus is calculated as a function of the number of condensed atoms. In the presence of dissipation, the amplitude of the oscillation will increase, eventually resulting in self-annihilation of the ring., 8 pages, 7 figures, ReVTex

Vortex structures in dilute quantum fluids are studied using the Gross-Pitaevskii equation. The velocity and momentum of multiply quantized vortex rings are determined and their core structures analysed. For flow past a spherical object, we study the encircling and pinned ring solutions, and determine their excitation energies as a function of the flow velocity for both penetrable and impenetrable objects. The ring and laminar flow solutions converge at a critical velocity, which decreases with increasing object size. We also study the vortex solutions associated with flow past a surface bump which indicate that surface roughness also reduces the critical velocity. This effect may have important implications for the threshold of dissipation in superfluids and superconductors., 7 pages, 16 postscript files for 6 figures

Total cross sections for electron capture are calculated for collisions of fast protons and alpha-particles with atomic hydrogen. The distorted- wave impulse approximation is applied over the energy range 10-1500 keV/u. State-selective results are given for the 1s, 2s and 2p levels. Both the 'post' and 'prior' forms of the model are calculated and compared with results from other theories and experimental measurements. In general the model performs very well in comparison with experiment over this energy range though discrepancies arise at lower energies., 13 pages of text and 6 postscript figures, to be published in J. Phys. B: At. Mol. Opt. Phys

The energy dependence of the nonradiative electron capture cross-section is discussed in the relativistic domain. A simple analytic expression is obtained for inner-shell transitions using second-order perturbation theory. We have confirmed that the leading-order term is found to have the following energy dependence: Q ~ E^{-1}ln^2 E. This is attributed to a combination of kinematic features of the process and retardation effects. Electron capture without change of spin is the dominant transition., Comment: LaTeX, 12 pages (Submitted to J.Phys.B - under review)

The XXVII International Conference on Photonic, Electronic and Atomic Collisions was held at Queen's University Belfast, Northern Ireland, 27 July – 2 August 2011. Members of the Local Organising Committee were drawn from the School of Mathematics and Physics of Queen's University Belfast, the School of Physical Sciences at Dublin City University, the School of Physics at University College Dublin and the Department of Experimental Physics at the National University of Ireland, Maynooth. The Conference was attended by 566 participants with contributions from 54 countries. The meeting attracted 786 contributed papers for presentation in the poster sessions. The conference included 20 Special Reports selected from the contributed papers, and these are included in part 1 of this volume. During the meeting a total of 65 Progress Reports were also presented, and the authors invited to submit written versions of their talks (see Part 1). Of the total number of contributed papers, 663 are included as refereed abstracts in parts 2 to 15 of this volume of Journal of Physics: Conference Series. Part 1 of this volume includes detailed write-ups of the majority of plenary lectures, progress reports and special reports, constituting a comprehensive tangible record of the meeting, and is additionally published in hard-copy as the Conference Proceedings. There were 5 plenary lectures given by Margaret Murnane on Ultrafast processes in atomic dynamics; Chris Greene on Few-body highly-correlated dynamics; Michael Allan on Electron-molecule collisions; Yasunori Yamazaki on Antiproton and positron collisions and Thomas Stohlker on Relativistic ion collisions. Ian Spielman, winner of the IUPAP Young Scientist Prize for 2011, gave a special lecture entitled Modifying interatomic interactions using Raman coupling: a tale of slowly colliding Bose-Einstein condensates. In addition an evening public lecture by Mike Baillie on How precise tree-ring dating raises issues concerning the frequency of extraterrestrial impacts drew an attentive and appreciative audience. The editors are indebted to Tara Spencer for her exceptional organisation skills and support in compiling this volume. Thanks are also due to Ian Stewart for his assistance with gathering and indexing the documents. We would also like to express our sincere appreciation to the ICPEAC sponsors for their financial support. I D Williams Queen's University Belfast H W van der Hart Queen's University Belfast J F McCann Queen's University Belfast D S F Crothers Queen's University Belfast EDITORS

We investigate the ultracold, elastic-scattering of a trapped atom and a trapped ion. The low-energy potential surfaces of the [174Yb−87Rb]+ are estimated and the polarizability and higher-order multipole coefficients are obtained from ab initio calculations. The polarizability of the Ytterbium atom is well reproduced and the scattering length is estimated. The excited-state Yb+-Rb system is analysed in detail with a view to applications in hybrid ion-atom traps.