Measurement on the $M$-shell x-ray production cross sections are reported for Pb and Bi induced by the highly charged F (only on Pb) and C ions (on both). The energy of the incident ions was varied between 20 and $102\mathrm{MeV}$. We have derived the absolute cross sections for $M\alpha \beta$ and $M\gamma$ lines as well as the total $M$ x-ray cross sections. The measured cross sections are compared with available theoretical calculations, namely, the ECPSSR based on the perturbed-stationary state approximation including the effects due to the increased binding energy, Coulomb deflection $\left(C\right)$, energy-loss $\left(E\right)$, and relativistic $\left(R\right)$ wave function. The energy shifts and the intensity ratios of $M\alpha \beta$ and $M\gamma$ lines are shown to depend on the projectile atomic number. The $M\gamma$ x-ray cross sections are unusually higher compared to the ECPSSR prediction that is primarily attributed to a dramatic enhancement in the $M_3$-subshell fluorescence yield owing to multiple vacancies in $N$ subshells. This enhancement has been quantified and it is shown that the enhancement depends on the projectile atomic number. In addition we have derived the x-ray cross section arising due to $M\text{−}K$-shell electron transfer from a study of a charge state dependence of $M$-shell x-ray yields.

We study the properties of vortex states of a trapped Bose gas in the large-gas-parameter regime. To test the validity of the Gross-Pitaevskii theory in this regime for vortex states, we compare the results of the Gross-Pitaevskii and the modified Gross-Pitaevskii calculations for the total energy, chemical potential, density profile, and frequency shift of the quadrupole modes of the collective oscillations of a harmonically trapped condensate carrying a single quantized vortex. We find that in the large-gas-parameter regime, two calculations give substantially different results for all the properties mentioned above.

We consider quasi-two-dimensional atomic or molecular Bose-Einstein condensates with both contact and dipole-dipole interactions. It is shown that as a consequence of the dimensional reduction, and within mean-field theory, the condensates do not develop unstable excitation spectra, even when the dipole-dipole interaction completely dominates the contact interaction.

We have measured the absolute energy-averaged cross section for the electron impact excitation of ${\mathrm{C}}^{2+}(2s2p{}^{3}P^o\to 2p^2{}^{3}P)$ from energies below threshold to $17\mathrm{eV}$ above, and present the measured absolute rate coefficients for this transition, for temperatures from ${10}^4$ to ${10}^5\mathrm{K}$. These rate coefficients are required for diagnostics of plasmas such as those found in astrophysical environments. The synchronous photon detection method with beams modulation and inclined electron and ion beams was used. Radiation at $117.6\mathrm{nm}$ from the decay of the excited ions back to the metastable state was detected using an absolutely calibrated optical system. The fractional population of metastable ${\mathrm{C}}^{2+}\left(2s2p{}^{3}P^o\right)$ in the incident ion beam was determined to be $0.42\pm 0.03\left(1.65\sigma \right)$. The rate coefficient for ${\log }_{10}\mathrm{T}=4.8$ was determined to be $1.01\times {10}^{-8}{\mathrm{cm}}^3{\mathrm{s}}^{-1}\pm 14\%$ at a 90% confidence $\left(1.65\sigma \right)$ level. The measured cross section is in agreement within experimental uncertainty with 6-term close-coupling $R$-matrix calculations and 90-term $R$ matrix with pseudostates calculations.

An updated high-energy universal scaling rule for single electron capture cross sections is presented for $A^{q+}+{\mathrm{H}}_2$ collisions. The current scaling rule is built empirically on experimental data using a wide range of projectile ions and collision energies. The inclusion of such a broad range of values results in a model that more accurately predicts the single capture cross sections for a much wider range of collision systems. The current scaling rule is compared to three similar scaling rules to illustrate how using limited data to develop a universal scaling rule effects a models general predictive power. The effects of all four scaling rules on both experimental and theoretical data are examined.

The ionization of xenon Rydberg atoms excited to the lowest states in the $n=17$ and $n=20$ Stark manifolds at a flat $\mathrm{Au}\left(111\right)$ surface is investigated. Despite the strong perturbations in the energies and structure of the atomic states that occur as the surface is approached, it is shown that, under appropriate conditions, each incident atom can be detected as an ion and that the experimental data can be well fit by assuming that the ionization rate on average increases exponentially as the surface is approached. The ionization rates are compared to theoretical predictions.

Fluorescence line profiles and their implications on the cooling dynamics of the ${\mathrm{Mg}}^{+}$ ions stored in a linear rf trap are studied. The line profile is dictated by the temperature of the ion cloud at different laser detunings. The upper bound of the lowest temperature was estimated for different values of the rf trapping potential amplitude and the buffer gas pressure. A general trend of this ultimate temperature to increase with the rf trapping voltage and buffer gas pressure is expected, with an abrupt change at some critical value corresponding to the transition to and from a strongly correlated liquid or crystal state. While on the one hand this expectation was confirmed when the buffer gas pressure was varied; on the other hand the influence of the amplitude of the trapping voltage on the ultimate temperature shows an interesting new feature of first dipping down before the sharp increase occurs.

Using the example of electron-atom scattering in a strong laser field, it is shown that the oscillatory structure of the scattered electron spectrum can be explained as a consequence of the interference of the real electron trajectories in terms of Feynman’s path integral. While in previous work on quantum-orbit theory the complex solutions of the saddle-point equations were considered, we show here that for the electron-atom scattering with much simpler real solutions a satisfactory agreement with the strong-field-approximation results can be achieved. Real solutions are applicable both for the direct (low-energy) and the rescattering (high-energy) plateau in the scattered electron spectrum. In between the plateaus and beyond the rescattering cutoff good results can be obtained using the complex (quantum) solutions and the uniform approximation. The interference of real solutions is related to the recent attosecond double-slit experiment in time.

In this paper we calculate the effect of spin-exchange collisions in alkali-metal vapors. In the framework of the high-energy approximation, we evaluate the spin-exchange cross sections related to the line broadening and to the frequency shift of the ground state hyperfine transition. We do the calculation for the four isotopes, ${}^{23}\mathrm{Na}$, ${}^{39}\mathrm{K}$, ${}^{87}\mathrm{Rb}$, and ${}^{133}\mathrm{Cs}$. The results are used in particular to evaluate the spin-exchange frequency shift in Rb vapor cell frequency standards used in many applications. It turns out that, due to possible fluctuations in the atomic density, spin exchange may affect significantly the medium and long term frequency stability of the frequency standard.

Using the finite-temperature path integral Monte Carlo method, we investigate dilute, trapped Bose gases in a quasi-two-dimensional (quasi-2D) geometry. The quantum particles have short-range, $s$-wave interactions described by a hard-sphere potential whose core radius equals its corresponding scattering length. The effect of both the temperature and the interparticle interaction on the equilibrium properties such as the total energy, the density profile, and the superfluid fraction is discussed. We compare our accurate results with both the semiclassical approximation and the exact results of an ideal Bose gas. Our results show that for repulsive interactions (i) the minimum value of the aspect ratio, where the system starts to behave quasi-2D, increases as the two-body interaction strength increases; (ii) the superfluid fraction for a quasi-two-dimensionally Bose gas is distinctly different from that for both a quasi-1D Bose gas and a true 3D system, i.e., the superfluid fraction for a quasi-2D Bose gas decreases faster than that for a quasi-1D system and a true 3D system with increasing temperature, and shows a stronger dependence on the interaction strength; (iii) the superfluid fraction for a quasi-2D Bose gas lies well below the values calculated from the semiclassical approximation; and (iv) the Kosterlitz-Thouless transition temperature decreases as the strength of the interaction increases.

We study the quantum entanglement produced by a head-on collision between two Gaussian wave packets in three-dimensional space. By deriving the two-particle wave function modified by $s$-wave scattering amplitudes, we obtain an approximate analytic expression of the purity of an individual particle. The loss of purity provides an indicator of the degree of entanglement. In the case the wave packets are narrow in momentum space, we show that the loss of purity is solely controlled by the ratio of the scattering cross section to the transverse area of the wave packets.

Ultrashort, intense laser-cluster interaction and the resultant structure formation are investigated in detail by employing a particle-in-cell code including relaxation and ionization processes. In addition to a laser-induced polarization field, we have found that an ambipolar radial electric field and internal and external sheath fields play a key role in the explosion dynamics of the cluster. Electrons and ions show complex behavior leading to a prominent dip in the structure of the electron energy distribution, and a double-layered structure in ion density and energy distributions for higher charge states.

Low temperatures are necessary for the observation of strongly correlated quantum phases of fermionic atoms in optical lattices. We analyze how the temperature of a Fermi gas is altered when the fermions are loaded into an optical lattice with an underlying harmonic confining potential, and show how the temperature can be measured. The temperature of the atoms in the optical lattice determines the fraction of doubly occupied lattice sites of a two-component Fermi gas. We analytically calculate this quantity and find a strong temperature dependence. This fraction can be measured by studying the production of molecules in the lattice using a Feshbach resonance, which allows for precise thermometry of atoms in an optical lattice.

We introduce a new scheme to design optical microcavities supporting high-$Q$ modes with unidirectional light emission. This is achieved by coupling a low-$Q$ mode with unidirectional emission to a high-$Q$ mode. The coupling is due to enhanced dynamical tunneling near an avoided resonance crossing. Numerical results for a microdisk with a suitably positioned air hole demonstrate the feasibility and the potential of this concept.

We consider the problem of fault tolerance in the graph-state model of quantum computation. Using the notion of composable simulations, we provide a simple proof for the existence of an accuracy threshold for graph-state computation by invoking the threshold theorem derived for quantum circuit computation. Lower bounds for the threshold in the graph-state model are then obtained from known bounds in the circuit model under the same noise process.

High resolution laser spectroscopy of the $6s{}^{2}S_{1∕2}\to 6p{}^{2}P_{1∕2}$ transition ($D_1$ line) in neutral ${}^{133}\mathrm{Cs}$ is performed in a highly collimated thermal atomic beam by use of a femtosecond laser frequency comb and narrow-linewidth diode laser. The diode laser is offset locked to a single frequency component of the femtosecond laser frequency comb and probes the optical transitions between selected pairs of ground-state and excited-state hyperfine components. A photodiode detects the excited-state decay fluorescence, and a computerized data acquisition system records the signal. The Doppler shift is eliminated by orienting the laser beam in a direction perpendicular to the atomic beam to within a precision of $5\times {10}^{-6}\mathrm{rad}$. Optical frequencies for all four pairs of hyperfine components are measured independently, from which the $D_1$ line centroid and excited-state hyperfine splitting are obtained by least-squares minimization with the ground-state splitting as a fixed constraint. We find the $D_1$ line centroid to be $f_{D_1}=335116048748.1\left(2.4\right)\mathrm{kHz}$, and the $6p{}^{2}P_{1∕2}$ state hyperfine splitting to be 1 167 723.6(4.8) kHz. These results, in combination with the results of an atom interferometry experiment by Wicht et al. [Phys. Scripta T 102, 82 (2002)], are used to calculate a new value for the fine-structure constant.

Ionization and high-order harmonic generation of the one-dimensional (1D) ${\mathrm{H}}_2$ molecule in intense ultrashort laser fields are investigated using several current approximations for electron dynamics. Single- and double-ionization probabilities are compared with exact results. It is found that for the ground state $X{}^1\Sigma _g^{+}$, time-dependent extended Hartree-Fock gives generally comparable results except in the plateau region. The adiabatic local density approximation and time-dependent optimized effective potential with self-interaction correction (TDKLI) methods underestimate the ionization probabilities with no plateau and knee for double ionization contrary to the exact results. For the triplet excited state $A{}^3\Sigma _u^{+}$, where exchange is important, the TDKLI results agree well with the exact results. The exact double-ionization probabilities suggest the need for accurate pair-correlation functions.

We present a first-principles derivation of spatial atomic-sublevel decoherence near dielectric and metallic surfaces. The theory is based on the electromagnetic-field quantization in absorbing dielectric media. We derive an expression for the time variation of the off-diagonal matrix element of the atomic density matrix for arbitrarily shaped substrates. For planar multilayered substrates we find that for small lateral separations of the atom’s possible positions the spatial coherence decreases quadratically with the separation and inversely to the squared atom-surface distance.