We have studied the energy and angular distributions of low-energy electron emission in collisions of bare carbon ions of 1-MeV/u energy with He and ${\mathrm{H}}_2$ targets. The double-differential cross sections (DDCS’s) are measured for electrons with energies between 0.5 and 300 eV emitted within an angular range of 15° to 160°. The large forward-backward asymmetry observed in the angular distributions is explained in terms of the two-center effect. Single differential cross sections (SDCS’s) and total cross sections are also derived by integrating the DDCS’s over emission angles and energies. The data are compared with different theoretical calculations based on the first Born, CDW (continuum-distorted-wave), and CDW-EIS (eikonal-initial-state) approximations. The angular distributions of DDCS’s and SDCS’s are shown to deviate largely from the predictions of the B1 calculations, and are in much better agreement with both the continuum distorted-wave models. The CDW approximation provides a better agreement with the data compared to the CDW-EIS approximation, especially at higher electron energies. The total ionization cross sections for all three targets are shown to follow a scaling rule approximately.

We discuss hollow atom formation and stabilization of electrons on ${\mathrm{Ar}}^{q+}$ following ${\mathrm{Ar}}^{q+}+{\mathrm{C}}_{60}\to {\mathrm{Ar}}^{\left(q-s\right)+}+\cdot \cdot \cdot$ collisions at $3.3q\hspace{0.5em}\mathrm{keV}$ $(q=4\mathrm{}–18).$ The experimental information consists of the final projectile charge-state distributions $f_q^s,$ i.e., the relative distributions of the number of stabilized electrons, s, and the corresponding mean values $〈s〉={\sum }_{s=1\mathrm{}}^q{\mathrm{sf}}_q^s$ as functions of q. We use the classical over-the-barrier model to deduce sequences of effective principal quantum numbers and find that the hollow atom formation is completed $3–{4a}_0$ above the surface of the ${\mathrm{C}}_{60}$ cage for all q. For $q<~8$ (filled L shells), the last electrons are transferred from delocalized outer ${\mathrm{C}}_{60}$ orbitals directly to the projectile M shell (side-feeding), while several intermediate shells are left open for larger q leading to further electron transfer at intermediate distances and simultaneous electron emission from higher projectile shells. At still closer distances, localized carbon K-shell electrons are transferred directly to the argon L $(q=10\mathrm{}$ and 11) and M shells $(q>~12).$ The direct transfer to the L shell of ${\mathrm{Ar}}^{10+}$ and ${\mathrm{Ar}}^{11+}$ is manifested as significant enhancements of $〈s〉$ for $q=10\mathrm{}$ and $q=11.\mathrm{}$

We simulate several methods which could be realized in the laboratory to probe the band excitation energies and the momentum distribution of a Bose-Einstein condensate inside an optical lattice. The values of the excitation energies obtained by the different methods agree within the accuracy of the simulation. The meaning of the results in terms of density and phase deformations is tested by studying the relaxation of a phase-modulated condensate toward the ground state.

We report a Bell-state preparation experiment. High-purity Bell states are prepared by using femtosecond pulse pumped nondegenerate collinear spontaneous parametric down-conversion. The use of a femtosecond pump pulse does not result in a reduction of quantum interference visibility in our scheme in which the postselection of amplitudes and other traditional mechanisms, such as using thin nonlinear crystals or narrow-band spectral filters are not used. Another distinct feature of this scheme is that the pump, the signal, and the idler wavelengths are all distinguishable, which is very useful for quantum communications.

We study the absorption line shape of a strongly degenerate Fermi gas confined in a harmonic trap. The absorption spectrum is calculated using both the exact summation and also the Thomas-Fermi approximation. In the latter case, relatively simple analytical expressions are obtained for the absorption line shape for a large number of trapped atoms. At zero temperature, the approximated line shape is characterized by a $(1\mathrm{}-z^2{)}^{5/2}$ dependence, which agrees well with the exact numerical calculations. At nonzero temperature, the spectrum becomes broader, although remains non-Gaussian as long as the fermion gas is degenerate. The changes in the trap frequency for an electronically excited atom can introduce an additional line broadening.

We analyze the short-time behavior of the survival probability in the frame of the Friedrichs model for different form factors. We have shown that this probability is not necessarily analytic at the time origin. The time when the quantum-Zeno effect could be observed is found to be much smaller than usually estimated. We have also studied the anti-Zeno period and have estimated its duration.

We have previously proposed a Hardy-type test of local realism that employs continuous variables. Here a generalization of the test is presented, which can achieve a much larger violation, as shown by example. An upper bound on the degree of violation obtainable with this system is also derived.

In this paper we describe a way to quantify the folkloric notion that quantum measurements bring a disturbance to the system being measured. We consider two observers who initially assign identical mixed-state density operators to a two-state quantum system. The question we address is to what extent one observer can, by measurement, increase the purity of his density operator without affecting the purity of the other observer’s. If there were no restrictions on the first observer’s measurements, then he could carry this out trivially by measuring the initial density operator’s eigenbasis. If, however, the allowed measurements are those of finite strength—i.e., those measurements strictly within the interior of the convex set of all measurements—then the issue becomes significantly more complex. We find that for a large class of such measurements the first observer’s purity increases the most precisely when there is some loss of purity for the second observer. More generally the tradeoff between the two purities, when it exists, forms a monotonic relation. This tradeoff has potential application to quantum state control and feedback.

We consider separating the problem of designing Hamiltonian quantum feedback control algorithms into a measurement (estimation) strategy and a feedback (control) strategy, and we consider optimizing desirable properties of each under the minimal constraint that the available strength of both is limited. This motivates concepts of information extraction and disturbance that are distinct from those usually considered in quantum information theory. Using these concepts, we identify an information tradeoff in quantum feedback control.

We show how to improve efficiency in preparing Bell states in a coupled two-quantum-dot system, which was introduced by Quiroga and Johnson [Phys. Rev. Lett. 83, 2270 (1999)]. A measurement of the state of a driven quantum laser field leads to wave-function collapse. This results in the highly efficient preparation of Bell states. The effect of decoherence on the efficiency of generating Bell states is also discussed in this paper. The results show that decoherence does not affect the relative weight of $|00〉$ and $|11〉$ in the output state, but does affect the efficiency of finding Bell states.

We present a scheme of atomic-state teleportation by using a quantum switch (QS). Based on the principle of QS and the quantum interference effect, a controlled-NOT operation between atom and cavity is proposed and used to transform the joint measurement of the von Neumann type into the discrete measurements. A detection method using several atoms resonantly interacting with field state is also presented to read out the field state in a cavity. The fidelity due to cavity dissipation is discussed. In our scheme, since the transfer of quantum information between atom and cavity is achieved by nonresonant atom-cavity interaction, three-bit classical information is transmitted from Alice to Bob to complete teleportation.

A theoretical analysis of nuclear-spin conversion in ethylene ${}^{13}{\mathrm{CCH}}_4$ has been performed. The conversion rate was found to be $\simeq 3\times {10}^{-4}$ ${\mathrm{s}}^{-1}/\mathrm{Torr},$ which is in qualitative agreement with the recently obtained experimental value. It was shown that the ortho-para mixing in ${}^{13}{\mathrm{CCH}}_4$ is dominated by spin-rotation coupling. Mixing of only two pairs of ortho-para levels was found to contribute significantly to the spin conversion.

The Colle-Salvetti functional for electron correlation in closed-shell systems [Theor. Chim. Acta 37, 329 (1975)] is revised by introducing a Gaussian resummation ansatz in order to approximate the higher than second-order terms in the Taylor expansion of the diagonal elements of the reference spin-reduced second-order density matrix. The correlation strength and the correlation energy per electron are revised accordingly; the latter is now analytic everywhere in space and rid of any spurious correlation effects from the asymptotic region. The range of the correlation hole due to the cusp condition is also investigated. We illustrate the proposed modifications as they apply to the helium and beryllium atoms. The revised model does as good a job as the original model in predicting the correlation energy, but there are profound differences with regard to the correlation energy per electron. In the original model, the electronic density is correlated almost uniformly, but we find this not to be the case if the above Gaussian resummation ansatz is employed.

Absolute multiple-ionization cross sections, ${\sigma }^{q+},$ of He $\mathrm{}(q=1,2\mathrm{}),$ Ne $(q=1,2,$ and 3), Ar $(q=1,2,$ and 3), Kr $(q=1,2,$ and 3), and Xe $(q=1,2,3,$ and 4) atoms have been determined for interactions with ${\mathrm{He}}^{+}$ ions in the 1.0–3.5-MeV impact energy range. Special care was taken to obtain the slow recoil-ion detection efficiencies, by measuring the recoil ions in coincidence with the ${\mathrm{C}}^{3+}$ capture channel and comparing these results with absolute single measurements. Comparison is made with the data available in the literature. The present results are in good agreement with the previously published data in the case of the helium target, but some nonsystematic discrepancies appear for heavier targets.

The ${\mathrm{He}}^{+}$ + Ne collision system, in which the projectile electron as well as the target electrons undergo inelastic transitions is investigated in the independent-particle model with a time-dependent screening potential. We use the basis generator method to solve the single-particle equations for all electrons and combine the transition probabilities statistically to calculate charge-state correlated and more inclusive total cross sections in the energy range of 10 to 1000 keV/amu. Good agreement with available experimental data is found except for the lowest projectile energies, where it is indicated that a more refined dynamical screening model is required. We demonstrate the importance of Pauli blocking for the electron transfer to the dressed projectile and discuss the role of the electron-electron interaction between projectile and target electrons, which is not included in our model.

Angle-resolved Auger and valence photoelectron spectra were measured over a 14-eV photon energy range across the ${\mathrm{Cl}}_2$ $2p$ ionization thresholds. The measurements were carried out using highly efficient time-of-flight spectrometers coupled with photons from the Atomic and Molecular undulator beamline of the Advanced Light Source and an advanced data-acquisition system. Auger-electron spectra of $2\overrightarrow{p}{\sigma }^{*}$ and $2\overrightarrow{p}\mathrm{nl}$ resonances were analyzed and the evolution of the resonant Auger to the normal Auger decay distorted by postcollision interaction was examined. We find that valence photoionization channels do not resonate strongly at the photon energies of the core-to-Rydberg excitation, in contrast to the strongly resonating ones observed in the HCl molecule. Auger decay spectra of the ${2p}^{-1}{\sigma }^{*}$ resonances showed no evidence of atomic transitions in ${\mathrm{Cl}}^{*},$ also in contrast to HCl. In addition, angular distribution of the photoelectron and Auger-electron lines was derived.

Low-energy electron emission is studied for $3.6-\mathrm{MeV}/u$ ${\mathrm{Au}}^{53+}$ impact on Ne and Ar using the first-Born and continuum-distorted-wave eikonal-initial-state (CDW-EIS) approximations. By using optimized effective potentials to represent the target atom, very good agreement is obtained between the CDW-EIS results and experiments. The comparison with the calculations using the first-Born approximation shows that the emission is very asymmetric, with a preferential emission into the forward direction. A detailed study of the emission from each initial orbital of the target atom reveals features in the spectra which can be related to the structure of the initial-state bound wave function.

A three-body scattering process in the presence of Coulomb interaction can be decomposed formally into two-body single channel scattering, two-body multichannel scattering, and genuine three-body scattering. The corresponding integral equations are coupled Lippmann-Schwinger and Faddeev-Merkuriev integral equations. We solve these by applying the Coulomb-Sturmian separable expansion method. We present elastic scattering and reaction cross sections of the $e^{+}+H$ system both below and above the $H(n=2\mathrm{})\mathrm{}$ threshold. We find excellent agreements with previous calculations in most cases.

The classical trajectory Monte Carlo method and the monocentric close-coupling Bessel expansion scheme are implemented to describe ionizing ${\mathrm{He}}^{2+}+\mathrm{H}\mathrm{}\left(1s\right)\mathrm{}$ collisions at the threshold of the high-impact-energy range. Ionization dynamics are pictured by showing the temporal evolution of both ionizing density and average velocity field. We emphasize that the classical and quantum-mechanical treatments of electronic motion yield very close descriptions of ionization.

A topological analysis of charge densities in ${\mathrm{Li}}_n\mathrm{Mg}$ and ${\mathrm{Li}}_n\mathrm{Be}$ clusters for $n=1\mathrm{}-6$ is presented. ${\mathrm{Li}}_n\mathrm{Be}$ clusters show a stronger bonding of the Li atoms with Be, as compared to ${\mathrm{Li}}_n\mathrm{Mg}$ clusters. The topology of the density shows that direct bonds between Li and impurity atoms have some closed-shell nature. Li-Li bonds are observed for clusters $n<~4$ in ${\mathrm{Li}}_n\mathrm{Mg}$ series, while for $n>~5,$ the Li atoms form bonds only with the impurity atom. The bonds in some of the clusters seem to be strained. In contrast to Mg, the direct bonding of Be atom with the host indicates the tendency of Be to become trapped.