This is a sequel to an earlier article on the theory of angular correlation for double photoionization. Here we consider the two-step double photoionization of a rare-gas atom under the influence of a polarized photon beam described by appropriate Stokes parameters. Cylindrical mirror analyzers are used to detect the outgoing electrons. Theoretical values of the correlation function are obtained for linearly polarized light. Two different situations are handled. In the first, the value of the correlation function is obtained keeping the photoelectron in a fixed direction. In the other case, the direction of the Auger electron is kept fixed. Comparison with experiments on xenon shows excellent agreement for the case of ${4d}_{5/2}$ photoionization followed by a subsequent ${\mathrm{N}}_5-{\mathrm{O}}_{23}{\mathrm{O}}_{23}^1{S}_0$ Auger decay for a linearly polarized incident photon of energy 94.5 eV [J. Phys. B, 26, 1141 (1993)].

Photodetachment of the ${\mathrm{Ps}}^{-}{(e}^{-}{e}^{+}{e}^{-})$ ion by high-energy photons $\left(ħ\omega \approx m_e{c}^2\right)$ is considered. Our present approach is essentially based on the analytical solution of the first-order perturbation equation with the Dirac-type Hamiltonian. The main goal is to produce the universal formulas for the photodetachment cross sections which can be used for photons with arbitrarily high energies. Also, we wanted to study the angular distribution of the emitted photoelectrons and consider correlations between the incident photon and emitted photoelectron. The obtained formulas for the photodetachment cross sections can also be used to describe relativistic photodetachment of arbitrary few-body systems with unit charges. In particular, it can be applied to the ${\mathrm{H}}^{-}$ ion and to the muonic molecules.

The inherently two-dimensional nature of the hydrodynamic expansion of large xenon clusters irradiated by intense laser fields is shown in measurements of ion and electron emission as a function of laser pulse duration. These reveal correlation between a resonance in energy absorption by the clusters and asymmetry in cluster expansion. An extension of the hydrodynamic model accounts for the observations; an earlier interpretation of the electron spectrum is found to be incorrect.

Plasmas have been created by irradiating atomic clusters of argon with high-contrast, ultrashort $(<\mathrm{}100\mathrm{}\mathrm{fs})$ laser pulses and recording the corresponding K-shell emission spectra. The high-resolution Ar K-shell spectra were analyzed using a theoretical two-temperature collisional-radiative model of irradiated atomic clusters incorporating the effects of highly energetic electrons $\left(\sim 5\mathrm{keV}\right).\mathrm{}$ Comparison of the measured spectrum with the calculations indicates that a supercritical density near $N_e=2\mathrm{}\times {10}^{22}{\mathrm{cm}}^{-3}$ was attained in the shortest-pulse and highest-contrast shots. Results from additional experiments using pulses on the order of 300–400 fs are also consistent with a hydrodynamic model of laser-cluster interactions.

We have extended the tunneling ionization model of Ammosov-Delone-Krainov (ADK) for atoms to diatomic molecules by considering the symmetry property and the asymptotic behavior of the molecular electronic wave function. The structure parameters of several molecules needed for calculating the ionization rates using this molecular ADK model have been obtained. The theory is applied to calculate the ratios of ionization signals for diatomic molecules with their companion atoms that have nearly identical binding energies. The origin of ionization suppression for some molecules has been identified. The predicted ratios for pairs with suppression $({\mathrm{D}}_2:\mathrm{Ar},$ ${\mathrm{O}}_2:\mathrm{Xe})$ and pairs without suppression $({\mathrm{N}}_2:\mathrm{Ar},$ CO:Kr) are in good agreement with the measurements. However, the theory predicts suppression for ${\mathrm{F}}_2:\mathrm{Ar},$ which is in disagreement with the experiment. The ionization signals of NO, ${\mathrm{S}}_2,$ and of SO have also been derived from the experimental data, and the results are also shown to be in agreement with the prediction of the present molecular ADK theory.

We study the physics of a rapidly rotating gas of ultracold atomic bosons, with an internal degree of freedom. We show that in the limit of rapid rotation of the trap the problem exactly maps onto that of noninteracting fermions with spin in the lowest Landau level. The spectrum of the real bosonic system is identical to the one of the effective fermions, with the same eigenvalues and the same density of states. When the ratio of the number of atoms to the spin degeneracy is an integer number, the ground state for the effective fermions is an integer quantum Hall state. The corresponding bosonic state is a fractional quantum Hall liquid whose filling factor ranges in the sequence $\nu =1/2,2/3,3/4,\dots ,$ as the spin degeneracy increases. Anyons with $1/2,1/3,1/4,\dots$ statistics can be created by inserting lasers with the appropriate polarizations. A special situation appears when the spin degeneracy equals the number of atoms in the gas. The ground state is then the product of a completely antisymmetric spin state and a $\nu =1\mathrm{}$ Laughlin state. In this case the system exhibits fermionic excitations with fermionic statistics although the real components are bosonic atoms.

We demonstrate the existence of localized oscillatory breathers for quasi-one-dimensional Bose-Einstein condensates confined in periodic potentials. The breathing behavior corresponds to position oscillations of individual condensates about the minima of the potential lattice. We deduce the structural stability of the localized oscillations from the construction. The stability is confirmed numerically for perturbations to the initial state of the condensate, to the potential trap, as well as for external noise. We also construct periodic and chaotic extended oscillations for the chain of condensates. All our findings are verified by direct numerical integration of the Gross-Pitaevskii equation in one dimension.

We analyze quantum correlation properties of a spinor-1 $\mathrm{}(f=1\mathrm{})\mathrm{}$ Bose-Einstein condensate using the Gell-Mann realization of SU(3) symmetry. We show that previously discussed phenomena of condensate fragmentation and spin mixing can be explained in terms of the hypercharge symmetry. The ground state of a spinor-1 condensate is found to be fragmented for ferromagnetic interactions. The notion of two-bosonic-mode squeezing is generalized to the two-spin $(U-V)$ squeezing within the SU(3) formalism. Spin squeezing in the isospin subspace (T) is found and is numerically investigated. We also provide results for the stationary states of spinor-1 condensates.

$P$-representation techniques, which have been very successful in quantum optics and in other fields, are also useful for general bosonic quantum-dynamical many-body calculations such as Bose-Einstein condensation. We introduce a representation called the gauge P representation, which greatly widens the range of tractable problems. Our treatment results in an infinite set of possible time evolution equations, depending on arbitrary gauge functions that can be optimized for a given quantum system. In some cases, previous methods can give erroneous results, due to the usual assumption of vanishing boundary conditions being invalid for those particular systems. Solutions are given to this boundary-term problem for all the cases where it is known to occur: two-photon absorption and the single-mode laser. We also provide some brief guidelines on how to apply the stochastic gauge method to other systems in general, quantify the freedom of choice in the resulting equations, and make a comparison to related recent developments.

Electron interference in mesoscopic devices irradiated by external nonclassical microwaves is considered. In the case of one-mode microwaves, it is shown that both the average intensity and the spectral density of the interfering electrons are sensitive to the quantum noise of the microwaves. The results for various quantum states of the microwaves are compared and contrasted with the classical case. Separable and entangled two-mode microwaves are also considered and their effect on electron average intensity and autocorrelation, is discussed.

Polarization entanglement of twin photons created in the process of parametric down-conversion is fully determined by the pump polarization when the pump, signal, and idler beams are collinear with the symmetry axis of the nonlinear crystal. We point out that in this situation a threefold rotational symmetry is needed for the process to occur. We describe the polarization entanglement of the twin photons in terms of correlations on the Poincaré sphere. The inherent nonconservation of the intrinsic angular momentum of light in this process is discussed.

The impact excitation and ionization of hydrogen (H)-like ions by antiprotons are studied by solving the time-dependent Schrödinger equation with a time-dependent generalized pseudospectral method in a wide scaled impact energy region (1 to 1000 keV). The validity region of the scaling relation is investigated by comparing the time-dependent calculations with the first Born approximation results. The numerical error and the validity region of the time-dependent generalized pseudospectral method have been explored. Based on the present study, we conclude that (i) the scaling relation of the ionization and excitation cross sections is valid for high-Z H-like ions or in the high-impact-energy regime for low-Z H-like ions; (ii) for given H-like ions, the scaling relation works better for the impact excitation to the dipole allowed transition than for the impact excitation to the dipole forbidden transition; and (iii) the time-dependent generalized pseudospectral method is not valid in a very weak perturbation system, which can be fairly studied by the time-independent methods. We also discuss the physical originations of the numerical observations.

Single ionization of helium by antiprotons in a wide energy range (5–1000 keV) has been studied by a self-interaction-free time-dependent density-functional theory. Our calculated single-ionization cross sections are in agreement with the experiments in the high-energy regime. The calculated single-ionization cross sections around the peak position are 20% lower than the recent close-coupling results as well as the experiment. In the low-energy regime, our results are lower than the close-coupling results, but still larger than the experimental one. A detailed comparison between our method and the close-coupling method is discussed. Our estimated ratios of double-to-single ionization are in agreement with the experimental measurements within a factor of 2 over the whole energy range. The limitation of the present method is discussed by comparing with the more complicated theoretical methods.

We present a static classical over-the-barrier model (OBM) for electron transfer between two isolated, infinitely conducting spheres with arbitrary and different electrical charges. This model is shown to be very useful for first estimates of single- and multiple-electron transfer cross sections in cluster-cluster collisions when the collision velocities are significantly lower than the typical target electron velocities. For faster collisions, more advanced models such as the dynamical OBM, or the time-dependent local density approximation (TDLDA) or the solutions of their semiclassical counterparts—the Vlasov equations have to be used. The latter two methods clearly provide the most detailed information on the electronic response, but they are also computationally very demanding and have, so far, only been used for collisions involving one cluster (and an atomic ion). We compare our static OBM results (in the limit in which one of the sphere radii approaches zero) with TDLDA and Vlasov calculations of cluster charging in ${\mathrm{Ar}}^{8+}-{\mathrm{Na}}_{40}$ collisions at different velocities to demonstrate that the present static OBM is valid at sufficiently low velocities. The static OBM is then used in a comparison with experimental target charge state distributions in ${\mathrm{C}}_{60}^{q+}-{\mathrm{C}}_{60}$ and ${\mathrm{C}}^{q+}-{\mathrm{C}}_{60}$ collisions at $0.01\sqrt{q}$ and $0.06\sqrt{q}{v}_0,$ respectively. Calculated electronic excitation of the projectile after two-electron transfer in ${\mathrm{C}}_{60}^{4+}-{\mathrm{C}}_{60}$ collisions readily explains the recently observed suppression of the transfer ionization channel in this reaction. Finally, we model the total projectile electron loss and dissociation cross section in highly protonated Lysozyme-oxygen $(\mathrm{Lys}-{\mathrm{H}}_9^{9+}-{\mathrm{O}}_2)$ collisions and make comparisons with recent experimental results at $0.01v_0.$

We use the mean-field approximation to simplify the master equation for sympathetic cooling of bosons. For the mean single-particle occupation numbers, this approach yields the same equations as the factorization assumption introduced in an early paper. The stationary or equilibrium solution of the resulting master equation for the one-body density matrix shows that the mean-field approximation breaks down whenever the fraction of condensate bosons exceeds 10% or so of the total. Using group-theoretical methods, we also solve the time-dependent master equation for the one-body density matrix. Given the time dependence of the mean single-particle occupation numbers, this solution is obtained by quadratures. It tends asymptotically towards the equilibrium solution.

The surface mode spectrum is computed self-consistently for dilute Bose-Einstein condensates, providing the temperature dependence of the surface-mode-induced vortex nucleation frequency. Both the thermodynamic critical frequency for vortex stability and the nucleation frequency implied by the surface excitations increase as the critical condensation temperature is approached from below. The multipolarity of the destabilizing surface excitation decreases with increasing temperature. The computed finite-temperature critical frequencies support the experimental observations and the zero-temperature calculations for vortex nucleation.

We study the process of photodissociation of a molecular Bose-Einstein condensate as a potential source of strongly correlated twin atomic beams. We show that the two beams can possess nearly perfect quantum squeezing in their relative numbers.

We simulate magnetic-resonance force microscopy measurements of an entangled spin state. One of the entangled spins drives the resonant cantilever vibrations, while the other remote spin does not interact directly with the quasiclassical cantilever. The Schrödinger cat state of the cantilever (i.e., two trajectories of the quasiclassical cantilever) reveals two possible outcomes of the measurement for both entangled spins.

For a special class of bipartite states we calculate explicitly the asymptotic relative entropy of entanglement $E_R^{\infty }$ with respect to states having a positive partial transpose. This quantity is an upper bound to distillable entanglement. The states considered are invariant under rotations of the form $\mathrm{O}\otimes \mathrm{O},$ where O is any orthogonal matrix. We show that in this case $E_R^{\infty }$ is equal to another upper bound on distillable entanglement, constructed by Rains. To perform these calculations, we have introduced a number of results that are interesting in their own right: (i) the Rains bound is convex and continuous; (ii) under some weak assumption, the Rains bound is an upper bound to $E_R^{\infty };$ (iii) for states for which the relative entropy of entanglement $E_R$ is additive, the Rains bound is equal to $E_R.$

Preparation of entangled pairs of coupled two-state systems driven by a bichromatic external field is studied. We use a system of two coupled spin-$\frac{1}{2}$ particles that can be translated into a three-state ladder model whose intermediate state represents the entangled state. We show that this entangled state can be prepared in a robust way with appropriate fields. Their frequencies and envelopes are derived from the topological properties of the model.