We present a universal coupled-mode-theory treatment of free-space scattering of waves from resonant objects. The range of applicability of the presented approach is fairly broad: it can be used for almost any linear wave system, as long as the resonant scatterer has either three-dimensional (3D) spherical or 2D cylindrical symmetry, or else is sufficiently smaller than the resonant wavelength of the incident wave. The presented framework, while being intuitive and analytically simple, can nevertheless provide quantitatively very accurate modeling of scattering cross sections, absorption cross sections, and many other quantities of interest. We illustrate this approach by showing how it applies to the particular examples of scattering of light from spherically symmetric resonant objects and atoms, and scattering of neutrons off nuclei.

We present a detailed theoretical description of the generation of stationary light pulses by standing-wave electromagnetically induced transparency in media comprised of stationary atoms such as ultracold gasses and solids. We show that, contrary to thermal gas media, the achievable storage times are limited only by the ground state dephasing rate of the atoms, making such media ideally suited for nonlinear optical interactions between stored pulses. Furthermore, we find significant quantitative and qualitative differences between the two types of media, which are important for quantum-information processing schemes involving stationary light pulses.

Using the Oak Ridge National Laboratory (ORNL) ion-atom merged-beams apparatus, the absolute, total single-electron-capture cross section has been measured for collisions of ${\mathrm{Ne}}^{2+}$ with deuterium (D) at center-of-mass (c.m.) collision energies of $59–949\mathrm{eV}∕\mathrm{u}$. With the high-velocity ion beams now available at the ORNL Multicharged Ion Research Facility, we have extended our previous merged-beams measurement to lower c.m. collision energies. The data are compared to all four previously published measurements for ${\mathrm{Ne}}^{2+}+\mathrm{H}\left(\mathrm{D}\right)$ which differ considerably from one another at energies $\lesssim 600\mathrm{eV}∕\mathrm{u}$. We are unaware of any published theoretical cross-section data for ${\mathrm{Ne}}^{2+}+\mathrm{H}\left(\mathrm{D}\right)$ at the energies studied. Early quantal rate coefficient calculations for ${\mathrm{Ne}}^{2+}+\mathrm{H}$ at eV/u energies suggest a cross section many orders of magnitude below previous measurements of the cross section at $40\mathrm{eV}∕\mathrm{u}$ which is the lowest collision energy for which experimental results have been published. Here we compare our measurements to recent theoretical electron-capture results for ${\mathrm{He}}^{2+}+\mathrm{H}$. Both the experimental and theoretical results show a decreasing cross section with decreasing energy.

We consider multipole transitions between Rydberg states in amplitude-modulated standing-wave ponderomotive potentials. For experimentally realizable depths of the ponderomotive potential, we find Rabi frequencies of tens of kilohertz. The transitions are not subject to dipole selection rules and allow for changes in the angular momentum quantum number up to about 5. The effects of energy level shifts caused by the ponderomotive potential are discussed.

In this work we find explicitly the decoherence-free subspace (DFS) for a two two-level system in a common squeezed vacuum bath. We also find an orthogonal basis for the DFS composed of a symmetrical and an antisymmetrical (under particle permutation) entangled state. For any initial symmetrical state, the master equation has one stationary state which is the symmetrical entangled decoherence-free state. In this way, one can generate entanglement via a common squeezed bath of the two systems. If the initial state does not have a definite parity, the stationary state depends strongly on the initial conditions of the system and it is a statistical mixture of states which belong to DFS. We also study the effect of the coupling between the two-level systems on the DFS.

We predict two-frequency spatial optical solitons formed in atomic systems where a Raman transition is adiabatically prepared near a maximally coherent state. Using numerical simulations, we demonstrate the stability of these solitons against perturbations and investigate soliton-soliton collision properties.

We study genuine tripartite entanglement shared among the spins of three localized fermions in the noninteracting Fermi gas at zero temperature. First, we prove analytically with the aid of entanglement witnesses that in a particular configuration the three fermions are genuinely tripartite entangled in spin. Then various three-fermion configurations are investigated in order to quantify and calculate numerically the amount of genuine tripartite entanglement present in the system. Further we give a lower and an upper limit to the maximum diameter of the three-fermion configuration below which genuine tripartite entanglement exists and find that this distance is comparable with the maximum separation between two entangled fermions. The upper and lower limit turn out to be very close to each other indicating that the applied witness operator is well suited to reveal genuine tripartite entanglement in the collection of noninteracting fermions.

The critical behavior of entanglement near a quantum phase transition has been studied intensely over the past few years. Few-body quantum systems show critical behavior near the ionization point. We investigate the scaling properties of the von Neumann entropy for an atomiclike system near the ionization threshold. Using finite size scaling methods we calculate the critical charge and the critical exponent associated to the von Neumann entropy. The parallelism between the behavior of entanglement near a quantum phase transition and the behavior of the von Neumann entropy in a critical few-body quantum system is analyzed.

A relativistic version of the coupled-cluster single-double (CCSD) method is developed for atoms with a single valence electron. In earlier work, a linearized version of the CCSD method (with extensions to include a dominant class of triple excitations) led to accurate predictions for energies, transition amplitudes, hyperfine constants, and other properties of monovalent atoms. Further progress in high-precision atomic structure calculations for heavy atoms calls for improvement of the linearized coupled-cluster methodology. In the present work, equations for the single and double excitation coefficients of the Dirac-Fock wave function, including all nonlinear coupled-cluster terms that contribute at the single-double level, are worked out. Contributions of the nonlinear terms to energies, electric-dipole matrix elements, and hyperfine constants of low-lying states in alkali-metal atoms from Li to Cs are evaluated and the results are compared with other calculations and with precise experiments.

In this paper we report electron yields and stopping power of protons colliding with surfaces of NaCl-type insulators formed with the alkali-metal ions ${\mathrm{Li}}^{+}$, ${\mathrm{Na}}^{+}$, ${\mathrm{K}}^{+}$, and ${\mathrm{Rb}}^{+}$ and the halides ${\mathrm{F}}^{-}$, ${\mathrm{Cl}}^{-}$, ${\mathrm{Br}}^{-}$, and ${\mathrm{I}}^{-}$. We also report fitted models for the static and dynamic polarization potentials of the eight ions of interest. The calculations are carried out within the shellwise local plasma approximation using the Levine-Louie response function, instead of the usual Lindhard one, to account for the ionization energy.

In a typical experiment aiming to control quantum dynamics phenomena, each molecule experiences the same temporal laser field, but with an amplitude that depends on the spatial location and orientation of the molecule in the laser beam. It is proved under commonly arising conditions that at least one optimal laser field exists which will control all molecules in the sample, regardless of their orientation or spatial location. The optimal laser field may consist of a multipolarization control containing up to three orthogonal, independently shaped components. The analysis also includes the prospect of multipartite control where the field couples distinct groupings of states (e.g., multiple vibronic states), but without direct coupling within a group of states. This conclusion shows that achieving quantum control is not a matter of striking a compromise over the sample diversity, but rather a task subject to optimization to reach the highest possible level of control for all molecules in the sample.

Using methods developed in quantum field theory in curved space we estimate the effects of the inhomogeneities and of a nonvanishing velocity on the depletion of a Bose-Einstein condensate within the hydrodynamical approximation.

The local density of states (LDOS) of the electromagnetic field on the surface of an absorbing dielectric microsphere at frequencies of the whispering-gallery modes (WGMs) is evaluated using the dyadic Green tensors of the electric and magnetic fields. In the calculation, the morphology-dependent resonances in the frequency dependence of the Mie coefficients are described analytically in terms of the resonant frequency and the partial quality factors which allow for light radiation and absorption. The Purcell factor of LDOS enhancement by WGMs is calculated to be proportional to the product of the quality factor and the squared ratio of the light wavelength to the sphere diameter. The ultimate values of the electric-field LDOS enhancement are estimated to be of the order of ${10}^7$ for a fused-silica microsphere in air. The efficiency of radiation of the resonant spontaneous emission from electric dipoles located near the surface outside of a sphere is determined. The characteristics of a dielectric microsphere are compared with those of other cavities.

We study the ground-state entanglement of one-dimensional harmonic chains that are coupled to each other by a collective interaction as realized, e.g., in an anisotropic ion crystal. Due to the collective type of coupling, where each chain interacts with every other one in the same way, the total system shows critical behavior in the direction orthogonal to the chains, while the isolated harmonic chains can be gapped and noncritical. We derive lower and most importantly upper bounds for the entanglement, quantified by the von Neumann entropy, between a compact block of oscillators and its environment. For sufficiently large size of the subsystems, the bounds coincide and show that the area law for entanglement is violated by a logarithmic correction.

Complete momentum maps of all fragments including neutrals arising from dissociative double ionization of $\mathrm{C}{\mathrm{Cl}}_4$ by electron impact have been obtained. The geometry of the dissociating dication is estimated from the momentum maps. The observation of $\mathrm{Cl}_2{}^{+}$ in the time-of-flight mass spectrum of the fragments, combined with the momentum distribution of correlated fragments, provides evidence that the geometry of the dissociating cation is significantly altered from the tetrahedral geometry of the parent neutral. These observations suggest relocation of certain atoms within the molecular ion during dissociation. The geometry of $\mathrm{C}\mathrm{Cl}_4{}^{2+}$ derived from the momentum maps is in conformity with the theoretically generated structure.

We analyze the error in trapped-ion, hyperfine qubit, quantum gates due to spontaneous scattering of photons from the gate laser beams. We investigate single-qubit rotations that are based on stimulated Raman transitions and two-qubit entangling phase gates that are based on spin-dependent optical dipole forces. This error is compared between different ion species currently being investigated as possible quantum-information carriers. For both gate types we show that with attainable laser powers the scattering error can be reduced to below current estimates of the fault-tolerance error threshold.

The electronic spectrum of atomic nobelium (element 102) is calculated in preparation for a planned experiment. The intermediate-Hamiltonian (IH) coupled-cluster method is applied to the ionization potential and excitation energies of the atom, using a large basis set $\left(37s31p26d21f16g11h6i\right)$ and correlating the outer 42 electrons. All the levels studied are obtained simultaneously by diagonalizing the IH matrix. The rows and columns of this matrix correspond to all excitations from correlated occupied orbitals to virtual orbitals in a large $P$ space $\left(8s6p6d4f2g1h\right)$, and the matrix elements are “dressed” by including excitations to the higher virtual orbitals ($Q$ space) at the coupled cluster singles-and-doubles level. Lamb shift corrections are included. The accuracy is assessed by applying the same method to ytterbium, the lighter homologue of No. The calculated ionization potential of Yb is within $3\mathrm{meV}$ of experiment, and the average error in the lowest 20 excitation energies of the atom is $300{\mathrm{cm}}^{-1}$. Nobelium is the heaviest element for which a reliable semiempirical estimate of the ionization potential exists, $6.65\left(7\right)\mathrm{eV}$; the calculated value of $6.632\mathrm{eV}$ is in excellent agreement. Transition amplitudes are obtained from an extensive relativistic configuration interaction calculation. The outstanding feature of the predicted nobelium spectrum is a very strong line at $30060{\mathrm{cm}}^{-1}$, with an amplitude $A=5.0\times {10}^8{\mathrm{s}}^{-1}$, corresponding to the $7s7p$ ${}^{1}P_1\to 7s^2$ ${}^{1}S_0$ transition. Putting the error limit conservatively at $0.1\mathrm{eV}$, we predict a strong feature in the No spectrum at $30100\pm 800{\mathrm{cm}}^{-1}$.

We experimentally studied the ionization and dissociation of methane, ethane, and propane in strong $8\mathrm{fs}$ laser fields at an intensity of several ${10}^{14}\mathrm{W}∕{\mathrm{cm}}^2$. Strong parent ions and abundant fragmental ions were observed for all three of these kinds of molecules. Our observations indicated that these molecules were first ionized under strong ultrashort laser fields and electron-ion pairs were produced. Driven by the remaining laser oscillating electric field, the parent ion and the correlated electron collided with each other. Depending on the electron-ion impact energy, the parent ion was excited to a dissociated state or a doubly charged state. The experimentally observed fragmental ions resulted from the recollision-induced dissociation of the singly charged parent ion or the Coulomb explosion of the doubly charged parent ion.