The Energy-Corrected Sudden (ECS) model is a well-established dynamical model to calculate rovibrational isotropic Raman linewidth and also to describe overlapping between lines through the off-diagonal elements of the relaxation matrix. The extension of this model to anisotropic Raman or infrared lines has been previously performed through the expansion of the tetradic (four indices) relaxation supermatrix elements in terms of dyadic (two indices) mechanical cross sections. This model required new parameters in the diagonal elements of the dyadic matrices that are the relaxation cross sections of rotational angular momentum and of its associated second-order tensor. In this paper, a new approach of the extension of the ECS model for anisotropic Raman and infrared branches is proposed, and developed on a strong physical basis. This new model only needs the original ECS parameters determined through a fit of the experimental isotropic Raman Q linewidths to generate anisotropic Raman and infrared linewidths as well as line mixing coefficients.

We consider a model for a Kerr medium in a planar resonator, which takes into account the vectorial character of the radiation field. We analyze the spatial behavior of quantum fluctuations around a steady state, with a roll-pattern configuration in the beam cross section, using a Langevin treatment based on the Wigner representation. The spatial distribution of the quantum fluctuations around the roll pattern is dominated by the neutral (or Goldstone) mode, corresponding to rigid spatial displacements of the pattern. The spatial configuration of the field immediately outside the cavity input-output mirror depends on the time window over which fluctuations are averaged: only when the time window is on the order of the cavity lifetime the output field fluctuations are qualitatively similar to that of the intracavity field. The quantum correlations among the fields in play, as described by the full multimode model, turn out to be in good agreement with those predicted by a simple three-mode model.

We studied high-order harmonic generation with a 30 fs laser at an intensity of $<2\mathrm{}\times {10}^{14}\hspace{0.5em}{\mathrm{W}/\mathrm{c}\mathrm{m}}^2$ in a quasistatic gas cell $(<~10\hspace{0.5em}\mathrm{mm})$ filled with argon $(<~90\hspace{0.5em}\mathrm{torr}).\mathrm{}$ To our knowledge, this is the first systematic study on the effect of propagation length and gas density on the conversion efficiency and spatial quality of high-order harmonics. As a result of phase-matched propagation, both the spatial quality and conversion efficiency of the 29th harmonic are successfully optimized to a Gaussian-like profile with a divergence of 4.5 mrad (full width at ${1/e}^2$ maximum) and a saturated efficiency. A quasi-two-dimensional simulation confirms the phase-matching effect.

We clarify some aspects of population dynamics of a level-crossing system, in which a periodic modulation of the relative energy is superimposed on the energy change with a constant velocity. For moderate values of the off-diagonal coupling, the temporal evolution of the system is well described by a transfer-matrix formalism. It is shown that the existence probability on one level shows a series of steplike changes both in the high-frequecy limit and the low-frequency limit of the periodic modulation, reflecting the quasiquantization of the oscillating field in the former case, while reflecting the multiple real crossings in the latter case.

We present lifetime measurements of the ${7D}_{3/2}$ and ${7D}_{5/2}$ levels of Fr. We use a time-correlated single-photon counting technique on a sample of ${}^{210}\mathrm{Fr}$ atoms confined and cooled in a magneto-optical trap. The upper state of the ${7P}_{3/2}$ trapping transition serves as the resonant intermediate level for two-photon excitation of the $7D$ states. A probe laser provides the second step of the excitation, and we detect the decay of the atomic fluorescence. Our measurements help extend the knowledge of this class of atomic wave functions in which correlation effects are very significant. We measure lifetimes of $73.6\pm 0.3\hspace{0.5em}\mathrm{ns}$ and $67.7\pm 2.9\hspace{0.5em}\mathrm{ns}$ for the ${7D}_{3/2}$ and ${7D}_{5/2}$ levels, respectively.

We have studied the ionization of lithium Rydberg atoms by pulsed microwave fields in the regime in which the microwave frequency is equal to or a subharmonic of the classical Kepler frequency of the two-body Coulomb problem. We have observed a series of resonances where the atom is relatively stable against ionization. The resonances are similar to those seen previously in hydrogen, but with significant quantitative differences. We also present measurements of the distribution of states that remain bound after the microwave interaction for initial states near one of the classical subharmonic resonances.

Using a high-resolution setup, we investigate the fragmentation of ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$ in intense 790 nm laser pulses with pulse widths of 28 fs and 80 fs. The measured ${\mathrm{H}}^{+}$ $\left({\mathrm{D}}^{+}\right)$ kinetic energies resulting from effective two-photon dissociation of ${\mathrm{H}}_2^{+}$ $\left({\mathrm{D}}_2^{+}\right)$ show a clear dependence on the pulse width and on the isotope. One-dimensional calculations reproduce these effects and show that they mainly originate from the ${\mathrm{H}}_2^{+}$ $\left({\mathrm{D}}_2^{+}\right)$ dissociation dynamics. Further, we find that the initial ionic state before dissociation is not simply given as a Franck-Condon distribution over unperturbed ionic states. Rather it is a complex mixture of initial wave packets (covering, however, a small energy range) created by multiphoton ionization of ${\mathrm{H}}_2$ and ${\mathrm{D}}_2$ at various times during the action of the pulse.

We present semiempirical calculations of long-range van der Waals interactions for two interacting metastable rare-gas atoms Ne through Xe. Dispersion coefficients $C_6$ are obtained for homonuclear molecular potentials asymptotically connecting to the ${\mathrm{ns}(3/2)\mathrm{}}_2{+ns(3/2)\mathrm{}}_2$ atomic states. The estimated uncertainty of the calculated $C_6$ dispersion coefficients is 4%.

We calculate projectile-electron loss cross sections in ultrarelativistic collisions with neutral atomic targets. To this end we employ the first-order perturbation theory and the eikonal approximation. We show that, in general, the following main effects should be included for a proper description of the projectile-electron loss in ultrarelativistic collisions: (i) the shielding effects of electrons of the neutral target, (ii) the relativistic effects in the motion of the electron in the projectile for heavy projectiles, and (iii) the nonperturbative effects in collisions with heavy targets, especially for light projectiles.

Neutron resonance spin-echo (NRSE) phenomena are investigated experimentally and theoretically. In our experiments, spin precession produced in a classical manner and by neutron resonance is combined as two arms of a spin-echo machine. A magnetic-field scan in the classical SE coil reveals a spin-echo signal of the precession produced by the NRSE arm. The neutron spin-flip probability $\rho$ in the resonance coils turns out to be a key parameter of the NRSE arm. The limiting cases $\rho =0\mathrm{}$ and $\rho =1\mathrm{}$ lead, respectively, to Larmor precession with phase ${\phi }_1$ in the static magnetic fields of the NR flippers or to NRSE precession with ${\phi }_2.$ The case $0<\mathrm{}\rho <1\mathrm{}$ produces quantum interference resulting in additional echoes with phases ${\phi }_3=({\phi }_1+{\phi }_2)/2\mathrm{}$ and ${\phi }_4=\pm \left({\phi }_1-{\phi }_2\right)/2.\mathrm{}$ The amplitude of each pattern depends on the spin-flip probability $\rho$ and the initial polarization. These experiments demonstrate explicitly the quantum-mechanical principle of linear spin state superposition of neutron particle waves, and the interference as a result of that.

We analyze both experimentally and theoretically the phase shift of a fixed coupling laser field in a Λ-type system induced by a tunable probe laser field. The measurements are performed with a heterodyne interferometer on a beam of cesium atoms in the $D_2$ line. This system exhibits electromagnetically induced transparency with a rapidly varying refractive index. The parametric dispersion of the coupling field over a range of six decades of coupling laser intensities is investigated and found to be in accord with the predictions from the semiclassical model.

We present an alternative method for measuring ultrashort extreme-ultraviolet pulses that can be synchronized with an intense infrared pulse. The method, based on photoionization of a target atom by the extreme-ultraviolet pulse in the presence of the infrared pulse, has a potential accuracy of close to 1 fs and is susceptible to single-shot operation. It is demonstrated on harmonic 15 of a titanium:sapphire laser. The minimum pulse duration that can be measured is limited only by the frequency of the radiation used for the ponderomotive shift of the ionization potential (3 fs in the case of the titanium:sapphire fundamental).

We calculate the Pancharatnam phase difference obtained when entangled two-photon states interfere. This phase depends nontrivially on the degree of entanglement between the photons forming the two-photon state. We outline an experiment where the entanglement dependence of the two-photon phase may be studied interferometrically. Also we propose how a cyclic version of this phase may be useful for implementing an efficient quantum gate.

The quantum topological phase of electric dipole circulating around the line of magnetic charges (monopoles) is discussed. We propose to mimic the line of magnetic monopoles using a ferromagnetic wire in which the magnetization is parallel to the wire and the magnitude of magnetization changes linearly along the wire. The phase shift in the proposed scheme is within the reach of present experimental techniques and may be observed in atomic or molecular interferometry.

We investigate the minimal resources that are required in the local implementation of nonlocal quantum gates in a distributed quantum computer. Both classical communication requirements and entanglement consumption are investigated. We present general statements on the minimal resource requirements and present optimal procedures for a number of important gates, including controlled-NOT (CNOT) and Toffoli gates. We show that one bit of classical communication in each direction is both necessary and sufficient for the nonlocal implementation of the quantum CNOT, while in general two bits in each direction is required for the implementation of a general two-bit quantum gate. In particular, the state swapper requires this maximum classical communication overhead. Extensions of these ideas to multiparty gates are presented.

In this paper the idea of holonomic quantum computation is realized within quantum optics. In a nonlinear Kerr medium the degenerate states of laser beams are interpreted as qubits. Displacing devices, squeezing devices, and interferometers provide the classical control parameter space where the adiabatic loops are performed. This results in logical gates acting on the states of the combined degenerate subspaces of the lasers, producing any one qubit rotations and interactions between any two qubits. Issues such as universality, complexity, scalability, and reversibility are addressed and several steps are taken towards the physical implementation of this model.

The L-shell Coster-Kronig yield $f_{23}$ has been measured for Dy, W, and Bi using an annular source double-reflection geometrical setup. Results for Dy, W, and Bi are $0.168\pm 0.013,\hspace{0.5em}0.146\pm 0.008,$ and $0.135\pm 0.011,$ respectively. These results are compared with available theoretical calculations.

Configuration interaction (CI) calculations were carried out for ${\mathrm{Ca}}^{+}$ $(4s{}^{2}S,$ $3d{}^{2}D,$ and $4p{}^2{P}^o),$ Ca ${(4s}^2{}^{1}S$ and $3d4s{}^{1}D),$ and ${\mathrm{Ca}}^{-}{(4s}^{2}4p{}^2{P}^o),$ studying the convergence of CI wave functions and energies with respect to both the one-electron and configuration bases. The effects of the Ar-like closed-shell core were included by considering excitations from the $3s$ and $3p$ subshells explicitly. The relativistic effects were estimated with Dirac-Fock calculations. The calculated ionization potentials were 6.080, 7.820, and 9.180 eV for $4s{}^{2}S,$ $3d{}^{2}D,$ and $4p{}^2{P}^o,$ respectively, compared with respective experimental values of 6.113, 7.810, and 9.255 eV. The calculated excitation energy for $3d4s{}^{1}D$ and electron affinity were 2.727 eV and 22 meV, respectively, which are in excellent agreement with the observed values of 2.709 eV and 21.3 meV.

A high-resolution pure $\mathrm{Cu}\hspace{0.5em}{K}^h{\alpha }_{1,2}$ hypersatellite spectrum was measured by photoexcitation using synchrotron radiation. A shift ${E(K}^h{\alpha }_2\left)-E\right(K{\alpha }_1)=281.4\mathrm{}\pm 0.3\hspace{0.5em}\mathrm{eV}$ from the diagram lines, a splitting ${E(K}^h{\alpha }_1\left)-{E(K}^h{\alpha }_2\right)=23.6\mathrm{}\pm 0.4\hspace{0.5em}\mathrm{eV},$ and an intensity ratio ${R=I(K}^h{\alpha }_1{)/I(K}^h{\alpha }_2)=0.29\mathrm{}\pm 0.02$ are found for the two lines of the spectrum. Full-spectrum fits based on ab initio Dirac-Fock calculations agree well with the measured spectrum, when QED corrections and Breit interaction are included. A slightly higher calculated R may indicate that the intermediate coupling is not fully accounted for. The intensity’s evolution from threshold (measured to be at $18.351\pm 0.015\hspace{0.5em}\mathrm{keV})$ shows an unexpectedly long saturation range extending up to $\sim 30\hspace{0.5em}\mathrm{keV}.$ The intensity evolution deviates from the Thomas model, which should be valid in the adiabatic, near-threshold regime. The implications of our results for the Z variation of the coupling, correlations, and atomic interactions across the $3d$ transition elements are discussed.

Charge transfer processes in collisions of ${\mathrm{F}}^{2+}$ ions with He atoms were studied by using the molecular representation below 600 eV energies. The ground ${\mathrm{F}}^{2+}{(}^{4}S)$ state and one excited ${\mathrm{F}}^{2+}{(}^{2}D)$ state are considered as the initial channels in order to examine the effect of the excited state. We have also investigated charge transfer processes in the reverse ion-ion collisions. Cross sections for nonradiative charge transfer in the ground quartet state ${\mathrm{F}}^{2+}+\mathrm{H}\mathrm{e}$ collisions are found to increase gradually with the impact energy and reach around $2\times {10}^{-16}{\mathrm{cm}}^2$ at 558 eV, while those from the doublet state also show a gradual increase and stay nearly constant with $1.2\times {10}^{-16}{\mathrm{cm}}^2$ at the same energy. Cross sections for the reverse processes for both symmetries are found to be very small with a magnitude less than ${10}^{-18}{\mathrm{cm}}^2$ due to the strong Coulomb repulsion between two ions, but rapidly increase as the collision energy increases to reach $3\times {10}^{-17}$ and ${10}^{-17}{\mathrm{cm}}^2$ for the quartet and doublet manifolds, respectively, at the highest energy studied.