A kinetic approach for the evolution of ultracold neutral plasmas including interionic correlations and the treatment of ionization/excitation and recombination/deexcitation by rate equations is described in detail. To assess the reliability of the approximations inherent in the kinetic model, we have developed a hybrid molecular dynamics method. Comparison of the results reveals that the kinetic model describes the atomic and ionic observables of the ultracold plasma surprisingly well, confirming our earlier findings concerning the role of ion-ion correlations [Phys. Rev. A 68, 010703 (2003)]. In addition, the molecular dynamics approach allows one to study the relaxation of the ionic plasma component toward thermodynamical equilibrium.

Recently, classical simulations of threshold photoionization in the presence of an electric field have shown that a clear distinction between direct and indirect trajectories followed by the outgoing electron can be observed in the patterns of electron impacts on a two-dimensional detector. Subsequently, slow photoelectron imaging experiments have been reported where this distinction could be observed in atomic xenon. Furthermore, using a magnifying electrostatic lens to improve the velocity-map imaging technique, oscillatory patterns were observed modulating the classical envelope that was measured in the experiments of Nicole et al. [Phys. Rev. Lett. 88, 133001 (2002)]. This extension of slow photoelectron imaging, called photoionization microscopy, relies on the existence of interferences between various trajectories by which the electron moves from the atom to the plane of observation. In this article we present the main experimental results obtained both in slow photoelectron imaging and in photoionization microscopy. The formation of the interference pattern is discussed in the framework of a semiclassical model that is described in detail elsewhere. The qualitative information that can be drawn from the experiments is discussed, and the potential applications of photoionization microscopy are considered. Particular attention is paid to the role of continuum Stark resonances that appear between the saddle point in the Coulomb+dc field potential and the field-free ionization limit.

The quantum wave-packet dynamics in a bound-bound state system at intermediate coupling strength, the $A$ and $b$ states in the ${\mathrm{Rb}}_2$ molecule coupled by spin-orbit interaction, was studied by ultrafast pump-probe molecular beam spectrocopy and quantum dynamical calculations. It was shown that even at elevated molecular temperatures the experimentally observed traces are characterized by dynamical interference structures of mesobatic, i.e., diabatic-adiabatic hybrid, kind. Two types of mesobatic motion were discerned: bistable, which occurs in both bound-unbound and bound-bound systems, and astable, which is particular to bound-bound systems at intermediate coupling strength. Contrary to previous expectations, the signatures of the quantum interference structures in pump-probe delay traces were found to be robust toward averaging over initial quantum states. It was shown that the spectral variations observed while tuning the pump pulse wavelength is a quantum matter-wave relative of the fringes observed in a pulsed optical Michelson interferometer.

We consider a degenerate charged Bose-Coulomb gas populating several discrete stationary boson bound states that are located in a spherical-symmetrical central Coulombian potential. Each such state is defined, through appropriate boundary conditions and normalization, by a so-called “nonlinear eigenstate” that is actually a solution of the coupled (linear) stationary Schrödinger-like Gross-Pitaevskii differential equation and the (nonlinear) Poisson equation. The corresponding eigenvalues allow us to define the energies of these degenerate boson states, much like the Koopmans orbital energy in atomic physics. This theory applies surprisingly well (compared with the corresponding Hartree-Fock results) to spherical-symmetrical $s$ orbital states in atomic physics (i.e., bosonlike restricted orbital states where the additional spin degree of freedom is already integrated out). Finally the superposition of two such stationary nonlinear eigenstates is investigated and given a semiclassical physical significance similar to a Thomas-Fermi approach. The resulting concepts apply particularly well (namely within an average 1% error bar with respect to spectroscopic data) to the $1s^2\text{‐}2s^2$ orbital states of the $3⩽Z⩽9$ atomic subsystems.

The classical-field approximation to cold weakly interacting bosons allows for a unified treatment of condensed and uncondensed parts of the system. Until now, however, the quantitative predictions were limited by a dependence of the results on a grid chosen for numerical implementation of the method. In this paper, we propose replacing this unphysical ambiguity by an additional postulate: the temperature of the gas at thermal equilibrium should be the same as that of an ideal Bose gas with the same fraction of condensed atoms. As it turns out, with this additional assumption, nearly all atoms are within the classical fields, thus the method applies to the whole system.

In an electromagnetic cavity, photons can be created from the vacuum state by changing the cavity’s properties with time. Using a simple model based on a massless scalar field, we analyze resonant photon creation induced by the time-dependent conductivity of a thin semiconductor film contained in the cavity. This time dependence may be achieved by irradiating periodically the film with short laser pulses. This setup offers several experimental advantages over the case of moving mirrors.

We proposed a scheme for generating arbitrary, discrete superpositions of motional coherent and squeezed coherent states of the quantized center of mass along a straight line in phase space for $N$ trapped ions. We also show that such a method can be used for the engineering of motional quantum states. Furthermore, these states should help to examine the dynamics behavior of various systems and might be used for applications in quantum information processing.

The phenomenon of electromagnetically induced transparency has been studied when a four-level atom is located in a photonic band gap material. Quantum interference is introduced by driving the two upper levels of the atom with a strong pump laser field. The top level and one of the ground levels are coupled by a weak probe laser field and absorption takes place between these two states. The susceptibility due to the absorption for this transition has been calculated by using the master equation method in linear response theory. Numerical simulations are performed for the real and imaginary parts of the susceptibility for a photonic band gap material whose gap-midgap ratio is 21%. It is found that when resonance frequencies lie within the band, the medium becomes transparent under the action of the strong pump laser field. More interesting results are found when one of the resonance frequencies lies at the band edge and within the band gap. When the resonance frequency lies at the band edge, the medium becomes nontransparent even under a strong pump laser field. On the other hand, when the resonance frequency lies within the band gap, the medium becomes transparent even under a weak pump laser field. In summary, we found that the medium can be transformed from the transparent state to the nontransparent state just by changing the location of the resonance frequency. We call these two effects anomalous electromagnetically induced transparency.

We propose a scheme to implement the quantum teleportation protocol with single atoms trapped in cavities. The scheme is based on the adiabatic passage and the polarization measurement. We show that it is possible to teleport the internal state of an atom trapped in a cavity to an atom trapped in another cavity with the success probability of $1∕2$ and the fidelity of 1. The scheme is resistant to a number of considerable imperfections such as the violation of the Lamb-Dicke condition, weak atom-cavity coupling, spontaneous emission, and detection inefficiency.

Based on an exact treatment of hard-core bosons confined on one-dimensional lattices, we obtain the large distance behavior of the one-particle density matrix, and show how it determines the occupation of the lowest natural orbital in the thermodynamic limit. We also study the occupation ${\lambda }_{\eta }$ of the natural orbitals for large-$\eta$ at low densities. Both quantities show universal behavior independently of the confining potential. Finite-size corrections and the momentum distribution function for finite systems are also analyzed.

The phenomenon of Euclidean resonance (a strong enhancement of quantum tunneling through a nonstationary potential barrier) is applied to disintegration of atoms and molecules through tunnel barriers formed by applied constant and time-dependent electric fields. There are two different channels for such disintegration, electronic and ionic. The electronic mechanism is associated with the ionization of a molecule into an electron and a positive ion. The required frequencies are in a wide range between $100\mathrm{MHz}$ and the infrared. This mechanism may constitute a method of selective destruction of chemical bonds. The ionic mechanism consists of dissociation of a molecule into two ions. Since an ion is more massive than an electron, the necessary frequency is about $1\mathrm{MHz}$. This provides the theoretical possibility of a different method of isotope separation by radio frequency waves.

We have extended the transition-state theory to describe the dynamics of core hole excitation. This allows us to interpret the abnormally bland near-edge x-ray absorption fine structure spectrum of the gas phase benzonitrile molecule at the N $1s$ edge. We have brought to light different paths for the two most intensive resonances, going from the linear to the bent structure. The profile of each resonance consists of two different vibrational progressions corresponding to stretching modes and a broad continuum of bending excited states.

A second-quantization formalism has been used to obtain a general expression for the generalized oscillator strength (GOS) for inner-shell electron transitions between two open shells of any atom. The present formula together with the spin polarized technique of the random-phase approximation with exchange are then employed to investigate correlation effects in the GOS for the $\mathrm{Na}2p^{6}3s\left({}^{2}S\right)\to 2p^{5}3s^2\left({}^{2}P\right)$ transition. Results are compared with those measured by Bielschowsky et al. [Phys. Rev. A 43, 5975 (1991)]. The present formula has also been used with Hartree-Fock wave functions to calculate the GOS’s for the carbon $2s^{2}2p^2\left({}^{3}P\right)\to 2s2p^3\left({}^{3}P\right)$ and $2s^{2}2p^2\left({}^{3}P\right)\to 2s2p^3\left({}^{3}D\right)$ transitions. The calculated multiplet oscillator strengths for the two transitions are compared with the experimental values.

We apply a many-body classical model and a semiclassical coupled-channel approach to study the electronic processes occurring in the course of fast collisions between atomic and molecular species. The methods are applied in a comparative study of electron transfer in ${\mathrm{He}}^{2+}∕{\mathrm{Ar}}^{2+}-\mathrm{H}_2{}^{+}$ collisions at $\mathrm{keV}{\mathrm{u}}^{-1}$ impact energies. The classical calculations are in agreement with recent experimental data [H. Bräuning et al., J. Phys. B 34, L321 (2001)] for projectile velocities larger than the initial electron velocity. The semiclassical model is based on the sudden approximation where the electronic wave function is expressed by linear combinations of traveling atomic capture states and target molecular states obtained at fixed nuclei. The related charge transfer cross sections are slightly underestimated (overestimated) for ${\mathrm{He}}^{2+}$ $\left({\mathrm{Ar}}^{2+}\right)$ when considering $\mathrm{H}_2{}^{+}$ in its initial vibrational ground state. These cross sections do, however, depend strongly on the internuclear distance of the hydrogen molecular ion: when involving an initial vibrational excitation of the target, the averaged cross sections obtained from the semiclassical approach become in fair agreement with experiments.

In the present paper, we model in a fully quantum-mechanical way the dynamics of an atom with one active electron interacting with a coherent linearly polarized ultrashort photonic pulse. We use path-integral methods. We derive the system’s propagator in its discrete form and develop a Monte Carlo method to study its dynamics. To avoid any additional complication, we apply our method to the ionization of atomic hydrogen from its ground state supposing that the photon energy is greater than the ionization threshold and give the ionization probability. In fact, the present method can be applied to the ionization of any atom or molecule.

The electronic structure of the lithium atom in a strong magnetic field $0⩽\gamma ⩽10$ is investigated. Our computational approach is a full configuration interaction method based on a set of anisotropic Gaussian orbitals that is nonlinearly optimized for each field strength. Accurate results for the total energies and one-electron ionization energies for the ground and several excited states for each of the symmetries ${}^{2}0^{+}$, ${}^2(-1)^{+}$, ${}^4(-1)^{+}$, ${}^4(-1)^{-}$, ${}^2(-2)^{+}$, ${}^4(-2)^{+}$, and ${}^4(-3)^{+}$ are presented. The behavior of these energies as a function of the field strength is discussed and classified. Transition wavelengths for linear and circular polarized transitions are presented as well.

We used a $\mathrm{Cs}$ fountain to measure the Stark shift of the ground-state hyperfine transition frequency in cesium $\left(9.2\mathrm{GHz}\right)$ due to the electric field of the blackbody radiation. The relative shift at $300\mathrm{K}$ deduced from our measurements, including the leading and the second-order term in temperature, is $(-1.45\pm 0.09)\times {10}^{-14}$ and agrees with our recent theoretical evaluation $(-1.51\pm 0.07)\times {10}^{-14}$ [Micalizio et al. Phys. Rev. A 69, 053401 (2004)]. These values differ from that currently used $(-1.735\pm 0.003)\times {10}^{-14}$, with significant implications on frequency standards accuracy, on clocks comparison and on a variety of high-precision physics tests, such as the time stability of fundamental constants.

Bloch-Siegert shifts and widths of resonances in two-level systems are evaluated within an adiabatic approximation applicable in the multiphoton regime. The level splitting is controlled by a static field. Most attention is paid to the case of a circular driving field with the static field in the plane of rotation. This nonconventional setup was used in a recent experiment on intrashell resonances in Rydberg atoms where shifts and widths for $N$-photon resonance with $N$ as large as 23 were observed [D. Fregenal et al., Phys. Rev. A 69, 031401(R) (2004)]. For this in-plane configuration the resonance widths are drastically enhanced compared to their values in the conventional configuration (linearly polarized driving field perpendicular to static field), whereas the shifts are only weakly affected.

This theoretical paper presents numerical calculations for the photoassociation of ultracold cesium atoms with a chirped laser pulse and a detailed analysis of the results. In contrast with earlier work, the initial state is represented by a stationary continuum wave function. In the chosen example, it is shown that an important population transfer is achieved to $\approx 15$ vibrational levels in the vicinity of the $v=98$ bound level in the external well of the $0_g^{-}(6s+6p_{3∕2})$ potential. Such levels lie in the energy range swept by the instantaneous frequency of the pulse, thus defining a “photoassociation window.” Levels outside this window may be significantly excited during the pulse, but no population remains there after the pulse. Finally, the population transfer to the last vibrational levels of the ground $a{}^3\sum _u^{+}(6\mathrm{s}+6\mathrm{s})$ state is significant, making stable molecules. The results are interpreted in the framework of a two-state model as an adiabatic inversion mechanism, efficient only within the photoassociation window. The large value found for the photoassociation rate suggests promising applications. The present chirp has been designed in view of creating in the excited state a vibrational wave packet that is focusing at the barrier of the double-well potential.

The dynamics of strongly interacting trapped dilute two-component Fermi gases (dilute in the sense that the range of interatomic potential is small compared with interparticle spacing) is investigated in a single-equation approach to the time-dependent density-functional theory. For the ground-state energy per particle of the system in the homogeneous phase, we have constructed an Padé parametrization based on Monte Carlo data and asymptotic behavior. Our numerical results for collective frequencies in the BCS-BEC crossover regime are in good agreement with recent experimental data obtained by the Duke University group. In addition, we show that the calculated corrections to the hydrodynamic approximation may be important, even for systems with a rather large number of atoms.