Transition rates and line strengths are calculated for electric-multipole ($E2$ and $E3$) and magnetic-multipole ($M1$, $M2$, and $M3$) transitions between $3s^{2}3p^{6}3d^{10}$, $3s^{2}3p^{6}3d^{9}4l$, $3s^{2}3p^{5}3d^{10}4l$, and $3s3p^{6}3d^{10}4l$ states (with $4l=4s$, $4p$, $4d$, and $4f$) in Ni-like ions with the nuclear charges ranging from $Z=34$ to 100. Relativistic many-body perturbation theory (RMBPT), including the Breit interaction, is used to evaluate retarded multipole matrix elements. Transition energies used in the calculation of line strengths and transition rates are from second-order RMBPT. Lifetimes of the $3s^{2}3p^{6}3d^{9}4s$ levels are given for $Z=34–100$. Taking into account that calculations were performed in a very broad range of $Z$, most of the data are presented in graphs as $Z$ dependences. The full set of data is given only for Ni-like W ion. In addition, we also give complete results for the $3d4s{{}^{3}D}_2-3d4s{{}^{3}D}_1$ magnetic-dipole transition, as the transition may be observed in future experiments, which measure both transition energies and radiative rates. These atomic data are important in the modeling of radiation spectra from Ni-like multiply charged ions generated in electron beam ion trap experiments as well as for laboratory plasma diagnostics including fusion research.

The energies of the 44 even-parity and 40 odd-parity $\left(4l4l^{\prime }\right)$ states of ions of the zinc isoelectronic sequence are determined through second order in relativistic many-body perturbation theory. Our calculations start from a Ni-like $V^{\left(N-2\right)}$ Dirac-Fock potential. Two alternative treatments of the Breit interaction are investigated. In the first approach, we omit Breit contributions to the Dirac-Fock potential and evaluate Coulomb and Breit-Coulomb corrections through second order perturbatively. This approach was used previously to evaluate the energies of Be-, B-, Mg-, and Yb-like systems. In the second approach, we include both Coulomb and Breit contributions to the Breit-Dirac-Fock potential and then treat the residual Breit and Coulomb interactions perturbatively. The results obtained from the two approaches are compared and discussed. Theoretical excitation energies are compared with critically evaluated experimental data and with results from other recent calculations. Trends of excitation energies including splitting of triplet terms as functions of nuclear charge $Z=34–100$ are illustrated graphically for some states. The resulting $Z$ dependence shows explicitly the effect of mixing of $\left[4p^2+4s4d\right]$, $\left[4d^2+4p4f\right]$, and $\left[4p4d+4s4f\right]$ configurations.

Asymptotically exact wave functions of the four-electron harmonium atom at the strong-correlation limit are given by Slater determinants multiplied by a Jastrow factor in the form of a single exponential function with the argument bilinear in the interelectron distances. The spin orbitals that enter the determinants set the multiplicities and angular momenta of individual states whereas the Jastrow factor fully accounts for the electron correlation. Asymptotically exact expressions for the corresponding electron densities, which can be computed from such wave functions with the help of the saddle-point approximation, have the form of products of Gaussian functions and polynomials in the Cartesian coordinates.

The triple differential cross section for electron-impact ionization of the $3p$ orbital of argon by $113.5\mathrm{eV}$ incident electrons has been measured using a magnetic angle changer in a conventional $(e,2e)$ spectrometer. Results are presented for $2\mathrm{eV}$ ejected electrons over an extended angular range, and over the complete coplanar scattering plane for $5\mathrm{eV}$ ejected electrons. The data reveal previously unobserved structures, and are compared with recent distorted-wave Born approximation (DWBA) and hybrid DWBA $R$-matrix calculations. Large discrepancies exist between experiment and both calculations in the accessed regions.

Collision dynamics of the ${\mathrm{He}}^{2+}+\mathrm{H}\left(1s\right)$ system imbedded in a Debye plasma is studied by the two-center atomic orbital close-coupling (AOCC) method in the energy range $5–300\mathrm{keV}∕\mathrm{u}$. The atomic orbitals and electron binding energies of atomic states are calculated within Debye-Hückel approximation of the screened Coulomb potential and used in AOCC dynamics formalism to calculate the state-selective electron capture and excitation cross sections. The basis contained 174 orbitals centered on the target (all $n\le 6$ discrete states and 117 quasicontinuum states) and 20 orbitals centered on the projectile (all $n\le 4$ discrete states). It is demonstrated that the screening of Coulomb interactions in the system progressively reduces the number of available excitation and electron capture channels when the screening parameter increases. The screening of Coulomb interactions introduces changes also in the values of direct and exchange couplings, thus affecting the magnitude and energy behavior of the cross sections. The control of dynamics of collision processes in a Debye plasma by varying the plasma screening of Coulomb interactions in the collision system is discussed.

The application of an exterior complex scaling method to an atomic scattering problem with distinct rearrangement channels is reported. Calculations are performed for positron-hydrogen collisions in an $s$-wave model employing an electron-positron potential of $V_{12}=-{\left[8+{\left(r_1-r_2\right)}^2\right]}^{-1/2}$, using the time-independent propagating exterior complex scaling method. This potential has the correct long-range Coulomb tail of the full problem and the results demonstrate that exterior-complex-scaling–based methods can accurately calculate scattering, ionization,and positronium formation cross sections in this three-body rearrangement collision.

We propose a method to generate broadband extreme ultraviolet supercontinuum harmonics by using the combination of a phase-stabilized few-cycle laser pulse and a low-frequency field. It is shown that this method can significantly modulate the quantum paths of the harmonics. The harmonic spectrum is extended to $I_p+8.2U_p$ and harmonics with a bandwidth of $4U_p$ become continuous. By adjusting the carrier-envelope phase of the few-cycle pulse, a close-to-Fourier-limit sub-50-as pulse is straightforwardly obtained.

The evolution of Bose-Einstein condensates is amply described by the time-dependent Gross-Pitaevskii mean-field theory which assumes all bosons to reside in a single time-dependent one-particle state throughout the propagation process. In this work, we go beyond mean field and develop an essentially exact many-body theory for the propagation of the time-dependent Schrödinger equation of $N$ interacting identical bosons. In our theory, the time-dependent many-boson wave function is written as a sum of permanents assembled from orthogonal one-particle functions, or orbitals, where both the expansion coefficients and the permanents (orbitals) themselves are time-dependent and fully determined according to a standard time-dependent variational principle. By employing either the usual Lagrangian formulation or the Dirac-Frenkel variational principle we arrive at two sets of coupled equations of motion, one for the orbitals and one for the expansion coefficients. The first set comprises of first-order differential equations in time and nonlinear integrodifferential equations in position space, whereas the second set consists of first-order differential equations with time-dependent coefficients. We call our theory multiconfigurational time-dependent Hartree for bosons, or $\text{MCTDHB}\left(M\right)$, where $M$ specifies the number of time-dependent orbitals used to construct the permanents. Numerical implementation of the theory is reported and illustrative numerical examples of many-body dynamics of trapped Bose-Einstein condensates are provided and discussed. The convergence of the method with a growing number $M$ of orbitals is demonstrated in a specific example of four interacting bosons in a double well.

We carried out an analysis based on sum rules and determined the radio-frequency spectroscopy shift observed in Chin et al.’s experiment [C. Chin, M. Bartenstein, A. Altmeyer, S. Riedl, S. Jochim, J. Denschlag, and R. Grimm, Science 305, 1128 (2004)]. It is shown that such a shift can be interpreted as spin correlations peculiar to a BCS-type state. An analytical form for the shift is obtained which enables us to make quantitative comparisons with the experiment throughout the crossover. We also calculated the width of the resonance. An interesting consequence is noticed, which can possibly be tested by future experiments.

We propose a universal transformation from a many-boson state to a corresponding many-fermion state in the lowest-Landau-level approximation of rotating many-body systems, inspired by the Laughlin wave function and by the Jain composite-fermion construction. We employ the exact-diagonalization technique for finding the many-body states. The overlap between the transformed boson ground state and the true fermion ground state is calculated in order to measure the quality of the transformation. For very small and high angular momenta, the overlap is typically above 90%. For intermediate angular momenta, mixing between states complicates the picture and leads to small ground-state overlaps at some angular momenta.

We develop a stochastic Gross-Pitaveskii theory suitable for the study of Bose-Einstein condensation in a rotating dilute Bose gas. The theory is used to model the dynamical and equilibrium properties of a rapidly rotating Bose gas quenched through the critical point for condensation, as in the experiment of Haljan et al. [Phys. Rev. Lett. 87, 210403 (2001)]. In contrast to stirring a vortex-free condensate, where topological constraints require that vortices enter from the edge of the condensate, we find that phase defects in the initial noncondensed cloud are trapped en masse in the emerging condensate. Bose-stimulated condensate growth proceeds into a disordered vortex configuration. At sufficiently low temperature the vortices then order into a regular Abrikosov lattice in thermal equilibrium with the rotating cloud. We calculate the effect of thermal fluctuations on vortex ordering in the final gas at different temperatures, and find that the BEC transition is accompanied by lattice melting associated with diminishing long-range correlations between vortices across the system.

We study mesoscopic superpositions of two component Bose-Einstein condensates. Atomic condensates, with long coherence times, are good systems in which to study such quantum phenomena. We show that the mesoscopic superposition states can be rapidly generated in which the atoms dispersively interact with the photon field in a cavity. We also discuss the production of compass states which are macroscopic quantum superposition states. The physical realization of mesoscopic states is important in studying decoherence and precision measurement.

We propose a scheme to generate temporal vector optical solitons in a lifetime broadened five-state atomic medium via electromagnetically induced transparency. We show that this scheme, which is fundamentally different from the passive one by using optical fibers, is capable of achieving distortion-free vector optical solitons with ultraslow propagating velocity under very weak drive conditions. We demonstrate both analytically and numerically that it is easy to realize Manakov temporal vector solitons by actively manipulating the dispersion and self- and cross-phase modulation effects of the system.

We analyze the Casimir force between two parallel infinite metal cylinders with nearby metal plates using two methods. Surprisingly, the attractive force between cylinders depends nonmonotonically on the separation from the plate(s), and the cylinder-plate force depends nonmonotonically on the separation of the cylinders. These multibody phenomenona do not follow from simple two-body force descriptions. We can explain the nonmonotonicity with the screening (enhancement) of the interactions by the fluctuating charges (currents) on the two cylinders and their images on the nearby plate(s).

We construct a single observable, measurement of whose mean value on four copies of an unknown two-qubit state is sufficient to determine unambiguously whether the state is separable or entangled. In other words, there exists a universal collective entanglement witness detecting all two-qubit entanglement. The test is directly linked to a function that characterizes the entanglement quantitatively to some extent. This function is an entanglement monotone under so-called local pure operations and classical communication which preserve local dimensions. Moreover, it provides tight upper and lower bounds for negativity and concurrence. An elementary quantum computing device estimating unknown two-qubit entanglement is designed.

We propose a strategy to achieve laser-field-free molecular orientation with the combination of an electrostatic field and an intense, nonresonant laser field with rapid turn off. The adiabatically created pendular state is effectively transferred to the rotational wave packet in the nonadiabatic regime after the rapid turn off of the laser pulse and the orientation achieved at the peak of the laser pulse is revived at the rotational period of the molecule with the same degree of orientation. The remarkable difference in molecular behavior is found between alignment and orientation, which reveals the crucial importance of the sufficiently long rising time of the laser pulse to achieve the highest possible degree of orientation. The feasibility has been examined for OCS molecules as a sample under practical experimental conditions.

A Markov approximation in open quantum dynamics can give unphysical results when a map acts on a state that is not in its domain. This is examined here in a simple example, an open quantum dynamics for one qubit in a system of two interacting qubits, for which the map domains have been described quite completely. A time interval is split into two parts and the map from the exact dynamics for the entire interval is replaced by the conjunction of that same map for both parts. If there is any correlation between the two qubits, unphysical results can appear as soon as the map conjunction is used, even for infinitesimal times. If the map is repeated an unlimited number of times, every state is at risk of being taken outside the bounds of physical meaning. Treatment by slippage of initial conditions is discussed.

We describe a method of extending Bell inequalities from $n$ to $n+1$ parties and formulate sufficient conditions for our method to produce tight inequalities from tight inequalities. The method is nontrivial in the sense that the inequalities produced by it, when applied to entangled quantum states may be violated stronger than the original inequalities. In other words, the method is capable of generating inequalities which are more powerful indicators of nonclassical correlations than the original inequalities.

The number of two-qubit gates required to deterministically transform a three-qubit pure quantum state into another is discussed. We show that any state can be prepared from a product state using at most three CNOT gates and that starting from the Greenberger-Horne-Zeilinger state, only two suffice. As a consequence, any three-qubit state can be transformed into any other using at most four CNOT gates. Generalizations to other two-qubit gates are also discussed.

We investigate the usefulness of a recently introduced five-qubit state by Brown et al. [I. D. K. Brown, S. Stepney, A. Sudbery, and S. L. Braunstein, J. Phys. A 38, 1119 (2005)] for quantum teleportation, quantum-state sharing, and superdense coding. It is shown that this state can be utilized for perfect teleportation of arbitrary single and two-qubit systems. We devise various schemes for quantum-state sharing of an arbitrary single- and two-particle state via cooperative teleportation. We later show that this state can be used for superdense coding as well. It is found that five classical bits can be sent by sending only three quantum bits.