For eight $\mathrm{H}\mathrm{C}{\mathrm{O}}^{+}$ rotational transitions we compare semiclassical and quantum calculations of the line broadening and shift induced by collisions with argon and helium atoms. A detailed analysis of the results allows better insights into the problem of the accuracy of the semiclassical model commonly used in most line shape studies.

An algorithm for determination of the exchange potential is constructed and tested. It represents a one-step procedure based on the equations derived by Krieger, Li, and Iafrate (KLI) [Phys. Rev. A 46, 5453 (1992)], implemented already as an iterative procedure by Kümmel and Perdew [Phys. Rev. Lett. 90, 043004 (2003)]. Due to suitable transformation of the KLI equations, we can solve them avoiding iterations. Our algorithm is applied to the closed-shell atoms, from Be up to Kr, within the DFT exchange-only approximation. Using pseudospectral techniques for representing orbitals, we obtain extremely accurate values of total and orbital energies with errors at least four orders of magnitude smaller than known in the literature.

There has been notable uncertainty regarding the degree of solvation of alkaline-earth-metals atoms, especially Mg, in free ${}^4\mathrm{He}$ nanodroplets. We have measured the electron energy dependence of the ionization yield of picked-up atoms. There is a qualitative shape difference between the yield curves of species solvated in the middle of the droplet and species located in the surface region; this difference arises from the enhanced role played by the Penning ionization process in the latter case. The measurements demonstrate that Mg, Ca, Sr, and Ba all reside at or near the droplet surface.

This paper presents state-selective field ionization spectra of highly excited Rydberg states of NO. The competition between electron-nuclear coupling and electron-field coupling is investigated and it is shown that the slew rate of the electric field can be exploited to control the rotational quantum state composition of field-ionized molecules.

We propose a technique which produces nearly complete ionization of the population of a discrete state coupled to a continuum by a two-photon transition via a lossy intermediate state whose lifetime is much shorter than the interaction duration. We show that using counterintuitively ordered pulses, as in stimulated Raman adiabatic passage (STIRAP), wherein the pulse coupling the intermediate state to the continuum precedes and partly overlaps the pulse coupling the initial and intermediate states, greatly increases the ionization signal and strongly reduces the population loss due to spontaneous emission through the lossy state. For strong spontaneous emission from that state, however, the ionization is never complete because the dark state required for STIRAP does not exist. We demonstrate that this drawback can be eliminated almost completely by creating a laser-induced continuum structure (LICS) by embedding a third discrete state into the continuum with a third control laser. This LICS introduces some coherence into the continuum, which enables a STIRAP-like population transfer into the continuum. A highly accurate analytic description is developed and numerical results are presented for Gaussian pulse shapes.

We investigate the effect of temperature on resonant and antiresonant dynamics in a dilute atomic gas kicked periodically by a standing-wave laser field. Our numerical calculations are based on a Monte Carlo method for an incoherent mixture of noninteracting plane waves, and show that the atomic dynamics are highly sensitive to the initial momentum width of the gas. We explain this sensitivity by examining the time evolution of individual atomic center-of-mass momentum eigenstates with varying quasimomentum, and we determine analytic expressions for the evolution of the second-order momentum moment to illustrate the range of behaviors.

It is shown that spin vortices are created through the Kibble-Zurek mechanism in the quantum phase transition of a spin-1 ferromagnetic Bose-Einstein condensate when the applied magnetic field is quenched to below a critical value. It is also shown that the spin correlation functions have finite correlation lengths, and that the magnetization at widely separated positions grows in random directions, resulting in spontaneous creation of spin vortices. We numerically confirm the scaling laws that the winding number of spin vortices is proportional to the square root of the length of a closed path and, for a slow quench, is proportional to ${\tau }_{\text{Q}}^{-1∕6}$ with ${\tau }_{\text{Q}}$ being the quench time. The relevance of spin conservation to the Kibble-Zurek mechanism is discussed.

We present a numerical study of noise correlations, i.e., density-density correlations in momentum space, in the extended fermionic Hubbard model in one dimension. In experiments with ultracold atoms, these noise correlations can be extracted from time-of-flight images of the expanding cloud. Using the density-matrix renormalization group method to investigate the Hubbard model at various fillings and interactions, we confirm that the noise correlations contain full information on the most important fluctuations present in the system. We point out the importance of the sum rules fulfilled by the noise correlations and show that they yield nonsingular structures beyond the predictions of bosonization approaches. Noise correlations can thus serve as a universal probe of order and can be used to characterize the many-body states of cold atoms in optical lattices.

We report the first full numerical analysis of polarization gratings (PGs), and study their most general properties and limits by using the finite-difference time-domain (FDTD) method. In this way, we avoid limiting assumptions on material properties or grating dimensions (e.g., no paraxial approximations) and provide a more complete understanding of PG diffraction behavior. We identify the fundamental delineation between diffraction regimes (thin versus thick) for anisotropic gratings and determine the conditions for $\approx 100\%$ diffraction efficiency in the framework of the coupled-wave $\rho$ and $Q$ parameters. Diffraction characteristics including the efficiency, spectral response, and polarization sensitivity are investigated for the two primary types of PGs with linear and circular birefringence. The angular response and finite-grating behavior (i.e., pixelation) are also examined. Comparisons with previous analytic approximations, where applicable, show good agreement.

An explicit calculation of conservation of probability and energy in a two-atom system is presented. One of the atoms is excited initially and undergoes spontaneous emission. The field radiated by this atom can be scattered by the second atom. It is seen that the Weisskopf-Wigner approximation must be applied using a specific prescription to guarantee conservation of probability and energy. Moreover, for consistency, it is necessary to take into account the rescattering by the source atom of radiation scattered by the second atom.

This article deals with the problem of gathering information on the time evolution of a single metastable quantum system whose evolution is impeded by the quantum Zeno effect. It has been found it is in principle possible to obtain some information on the time evolution and, depending on the specific system, even to measure its average decay rate, even if the system does not undergo any evolution at all.

We address the universal applicability of the discrete nonlinear Schrödinger equation. By employing an original but general top-down–bottom-up procedure based on symmetry analysis to the case of optical lattices, we derive the most widely applicable and simplest possible model, revealing that the discrete nonlinear Schrödinger equation is “universally” fit to describe light propagation even in discrete tensorial nonlinear systems and in the presence of nonparaxial and vectorial effects.

We analyze the quantum correlations between side modes of a quantum beat laser when a two-level atomic medium is driven strongly by a classical field. The squeezing and the entanglement generation of the cavity radiation are investigated. It turns out that there is neither squeezing nor entanglement when the strong driving field is resonant with the atomic transition but the generated light exhibits both two-mode squeezing and entanglement when the driving field is tuned away from the atomic transition.

We compare several optical implementations of phase-covariant cloning machines. The experiments are based on copying of the polarization state of a single photon in bulk optics by a special unbalanced beam splitter or by a balanced beam splitter accompanied by a state filtering. Also the all-fiber-based setup is discussed, where the information is encoded into spatial modes, i.e., the photon can propagate through two optical fibers. Each of the four implementations possesses some advantages and disadvantages that are discussed.

$K$-shell photodetachment of size-selected ${{\mathrm{B}}_2}^{-}$ and ${{\mathrm{B}}_3}^{-}$ cluster anions has been measured and calculated. The experimental absolute photodetachment cross sections exhibit bound resonances below threshold and two shape resonances above the $K$-shell threshold. Similar results were obtained for all of the cationic products observed, ${\mathrm{B}}^{+}$ and ${{\mathrm{B}}_2}^{+}$ from ${{\mathrm{B}}_2}^{-}$, as well as ${\mathrm{B}}^{+}$, ${{\mathrm{B}}_2}^{+}$, and ${{\mathrm{B}}_3}^{+}$ from ${{\mathrm{B}}_3}^{-}$. The overall agreement between measured and calculated photodetachment cross sections is very good. However, the theoretical study yielded additional bound resonances not observed in the experimental data.

We report the laser cooling and confinement of Cd atoms in a magneto-optical trap and characterize the loading process from the background Cd vapor. The trapping laser drives the ${}^{1}S_0\to {}^{1}P_1$ transition at $229\mathrm{nm}$ in this two-electron atom and also photoionizes atoms directly from the ${}^{1}P_1$ state. This photoionization overwhelms the other loss mechanisms and allows a direct measurement of the photoionization cross section, which we measure to be $2\left(1\right)\times {10}^{-16}{\mathrm{cm}}^2$ from the ${}^{1}P_1$ state. When combined with nearby laser-cooled and trapped ${\mathrm{Cd}}^{+}$ ions, this apparatus could facilitate studies in ultracold interactions between atoms and ions.

We present an ab initio three-dimensional (3D) calculation of multiphoton ionization (MPI) and high-order harmonic generation (HHG) of the hydrogen molecular ions subject to intense linearly polarized laser pulses. The orientation of the molecular axis with respect to the polarization of the laser field can be arbitrary. The numerical procedure involves the extension of the generalized pseudospectral (GPS) method for nonuniform spatial discretization of the Hamiltonian and wave functions and time propagation using the split-operator technique in the energy representation. The calculations were performed for the ground and two first excited electronic states of $\mathrm{H}_2{}^{+}$ at the internuclear separation $R=2.0\mathrm{a.u.}$ The laser pulse has a sine-squared envelope and contains 20 optical cycles with the wavelength $800\mathrm{nm}$. The dependence of MPI and HHG on the orientation angle is analyzed. We show that orientation effects are strongly affected by the symmetry of the wave function and the corresponding distribution of the electron density. While the anisotropy of MPI and HHG is rather weak for the $1{\sigma }_g$ state, both processes are suppressed at the orientation angle 90° for the $1{\sigma }_u$ state and at the angle 0° for the $1{\pi }_u$ state. We discuss the multiphoton resonance and two-center interference effects in the HHG spectra which can lead both to enhancement and suppression of the harmonic generation.

Dynamics and stability of solitons in two-dimensional (2D) Bose-Einstein condensates (BEC), with one-dimensional (1D) conservative plus dissipative nonlinear optical lattices, are investigated. In the case of focusing media (with attractive atomic systems), the collapse of the wave packet is arrested by the dissipative periodic nonlinearity. The adiabatic variation of the background scattering length leads to metastable matter-wave solitons. When the atom feeding mechanism is used, a dissipative soliton can exist in focusing 2D media with 1D periodic nonlinearity. In the defocusing media (repulsive BEC case) with harmonic trap in one direction and nonlinear optical lattice in the other direction, the stable soliton can exist. Variational approach simulations are confirmed by full numerical results for the 2D Gross-Pitaevskii equation.

A time-dependent multiconfigurational self-consistent field theory is presented to describe the many-body dynamics of a gas of identical bosonic atoms confined to an external trapping potential at zero temperature from first principles. A set of generalized evolution equations are developed, through the time-dependent variational principle, which account for the complete and self-consistent coupling between the expansion coefficients of each configuration and the underlying one-body wave functions within a restricted two state Fock space basis that includes the full effects of the condensate’s mean field as well as atomic correlation. The resulting dynamical equations are a classical Hamiltonian system and, by construction, form a well-defined initial value problem. They are implemented in an efficient numerical algorithm. An example is presented, highlighting the generality of the theory, in which the ballistic expansion of a fragmented condensate ground state is compared to that of a macroscopic quantum superposition state, taken here to be a highly entangled number state, upon releasing the external trapping potential. Strikingly different many-body matter-wave dynamics emerge in each case, accentuating the role of both atomic correlation and mean-field effects in the two condensate states.

Nuclear resonant scattering of synchrotron radiation was investigated simultaneously in the spatially incoherent $\left(4\pi \right)$ and in the spatially coherent (forward) scattering channels. A theory is presented which describes the main contributions to the scattering picture. To observe the $4\pi$ scattering, a nuclear target (spectator) was employed which was mounted downstream of another target (emitter). Emitter and spectator formed a combined scattering system. The time evolutions of the $4\pi$ scattering from the spectator and of the forward scattering from the combined system were measured and compared for different thicknesses of emitter and spectator. These observations and the analysis of the obtained time evolutions reveal how nuclear polaritons propagate through a scattering system.