We present molecular-orbital x-ray spectra from collision systems with highly charged projectiles calculated with a time-dependent coupled channel method using relativistic molecular Dirac-Fock-Slater wave functions and full radial and rotational couplings. The spectra of the system ${\mathrm{Cl}}^{16+}-\mathrm{Ar}$ are investigated with respect to the dynamics and the number of electrons in the system. Two basis sets have been employed in the calculation, one which belongs to the ground-state configuration and the other to the transition-state configuration on the incoming part of the trajectory respectively. Very good agreement with the experimental results is found by using the transition state basis set.

State-selective differential cross sections for single-electron capture processes in collisions of ${\mathrm{Ne}}^{q+}$ $(q=3\mathrm{}$ and 4) ions with ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$ have been studied experimentally at laboratory impact energies between 75 and 600 eV and scattering angles between $0°$ and $8°$ by means of a translational energy-gain spectroscopy technique. For the ${\mathrm{N}}_2$ target, zero-angle translational energy spectra show that the capture occurs mainly into $3s$ and $3d$ states of the projectile product ${\mathrm{Ne}}^{\left(q-1\right)+},$ respectively, for the ion charge states $q=3\mathrm{}$ and 4. For the ${\mathrm{O}}_2$ target, the dominant reaction channels are due to capture into $3p$ and ${3d}^{\prime },$ respectively, for charge states $q=3\mathrm{}$ and 4. In collisions of ${\mathrm{Ne}}^{3+}$ with ${\mathrm{N}}_2$ and ${\mathrm{O}}_2,$ contributions from processes commencing with a long-lived metastable state ${\mathrm{Ne}}^{3+}{(2p}^3{}^{2}D)$ are detected. Other channels due to capture accompanied by target excitation are found to open at large scattering angles. The angle and energy dependence of cross sections for single-electron capture by ${\mathrm{Ne}}^{q+}$ $(q=3\mathrm{}$ and 4) ions from ${\mathrm{N}}_2$ and ${\mathrm{O}}_2$ are also measured.

The $4d$ relative photoabsorption cross section of cesium has been observed to change dramatically in appearance along the isonuclear sequence Cs through ${\mathrm{Cs}}^{4+}.$ In each case, discrete structure is observed below threshold and for Cs through ${\mathrm{Cs}}^{2+},$ a giant dipole $4\overrightarrow{d}\varepsilon f$ resonance is also present above threshold. Between ${\mathrm{Cs}}^{2+}$ and ${\mathrm{Cs}}^{3+},$ there is a striking change, with much of the oscillator strength available in the $4\overrightarrow{d}f$ channel being abruptly transferred to the discrete spectrum. Despite the complexity of the transitions involved, the oscillator strength envelope for the discrete transitions yields relatively few features and remains essentially static in energy regardless of the parent terms. Hartree-Fock with configuration interaction and time-dependent local-density-approximation calculations successfully account for this behavior and permit identification of the discrete features.

The electronic structure of calcium clusters containing up to 13 atoms is studied within the general gradient approximation (GGA) of the density-functional formalism. For the calcium dimer it is observed that the exchange functional in GGA overestimates the binding energy, while a hybrid approach including Hartree-Fock exchange gives a better agreement with the experimental results. Binding energies, optimized geometries, vibrational frequencies, and thermodynamic properties have been calculated for several isomers at each cluster size. Various structures corresponding to saddle points of the energy curve are reported, along with the isomerization reaction path for ${\mathrm{Ca}}_5,$ ${\mathrm{Ca}}_6,$ and ${\mathrm{Ca}}_7.$ It was found that ${\mathrm{Ca}}_{12}$ undergoes a structural transition as a function of temperature, changing structure at T=317 K. A comparison of the minimum energy isomer geometry and binding energy obtained for each cluster size with those obtained from the Murrell-Mottram empirical potential shows that this potential overestimates the binding energies and does not adequately predict the optimized structures for several cluster sizes.

Emission of argon K-shell x rays produced upon irradiation of ${\mathrm{Ar}}_n(n=200\mathrm{}–{10}^4)$ clusters by intense ${(10\mathrm{}}^{14}–{10}^{16}\hspace{0.5em}{\mathrm{W}\mathrm{}\mathrm{cm}}^{-2}),$ femtosecond laser fields is probed as a function of the ellipticity of the impinging laser light. We observe no functional dependence of the K-shell x-ray emission on ellipticity. This is in contrast to polarization state dependences that have been observed in other facets of intense-laser interactions with gas-phase molecules, such as tunnel ionization and multiple tunnel ionization, above threshold ionization and high-order harmonic generation. Our data are rationalized using results of recent Monte Carlo simulations.

Several properties of trapped hard-sphere bosons are evaluated using variational Monte Carlo techniques. A trial wave function composed of a renormalized single-particle Gaussian and a hard-sphere Jastrow function for pair correlations is used to study the sensitivity of condensate and noncondensate properties to the hard-sphere radius and the number of particles. Special attention is given to diagonalizing the one-body density matrix and obtaining the corresponding single-particle natural orbitals and their occupation numbers for the system. The condensate wave function and condensate fraction are then obtained from the single-particle orbital with the highest occupation. The effect of interaction on other quantities such as the ground-state energy, the mean radial displacement, and the momentum distribution is calculated as well. Results are compared with mean-field theory in the dilute limit.

A hybrid formalism is considered for interacting classical and quantum sytems. This formalism is mathematically consistent and reduces to standard classical and quantum mechanics in the case of no interaction. However, in the presence of interaction, the correspondence principle is violated.

Suppose two distant observers Alice and Bob share a pure bipartite quantum state. By applying local operations and communicating with each other using a classical channel, Alice and Bob can manipulate it into some other states. Previous investigations of entanglement manipulations have been largely limited to a small number of strategies and their average outcomes. Here we consider a general entanglement manipulation strategy, and go beyond the average property. For a pure entangled state shared between two separated persons Alice and Bob, we show that the mathematical interchange symmetry of the Schmidt decomposition can be promoted into a physical symmetry between the actions of Alice and Bob. Consequently, the most general (multistep two-way-communications) strategy of entanglement manipulation of a pure state is, in fact, equivalent to a strategy involving only a single (generalized) measurement by Alice followed by one-way communications of its result to Bob. We also prove that strategies with one-way communications are generally more powerful than those without communications. In summary, one-way communications is necessary and sufficient for entanglement manipulations of a pure bipartite state. The supremum probability of obtaining a maximally entangled state (of any dimension) from an arbitrary state is determined, and a strategy for achieving this probability is constructed explicitly. One important question is whether collective manipulations in quantum mechanics can greatly enhance the probability of large deviations from the average behavior. We answer this question in the negative by showing that, given n pairs of identical partly entangled pure states $\left(|\Psi 〉\right)$ with entropy of entanglement $E\left(|\Psi 〉\right),$ the probability of getting $\mathrm{nK}$ $[K>E(|\Psi 〉\left)\right]$ singlets out of entanglement concentration tends to zero as n tends to infinity.

An apporach is presented in order to study the interelectronic correlation in few-electron atomic or molecular systems. The main point is that the correlation is described as a mutual collision between all the electrons. This approach allows the determination of simple wave functions for complex systems including only three parameters, with a clear physical meaning. The method is applied to study three- and four-electron systems in different states, including the so-called hollow states for lithium and beryllium. The overall results are found to be in good agreement with those deduced using much more sophisticated wave functions. Subsequently, the present wave functions are chosen as trial wave functions in the diffusion Monte Carlo method. This approach leads to a very accurate determination of the ground-state energies of lithium, lithium negative ion, and beryllium atoms, indicating that it becomes possible to deduce with very good accuracy some properties of relatively complex systems with a quite simple wave function.

Deviations from exponential decay dynamics have been proposed for a wide variety of systems in high-energy, atomic, and molecular physics. This work examines the quantum dynamics of a simple hierarchical local random matrix model. The hierarchical structure is imposed by two physically motivated constraints: an exponential size scaling of matrix elements, and a quantum number “triangle rule,” which introduces correlations in the quantum-state space by mimicking the nodal structure of wave functions in a coordinate Hamiltonian. These correlations lead to a systematic slowing of dephasing dynamics compared to exponential decays. A generalized Lorentzian line shape is introduced as the Fourier transform of a polynomial survival amplitude to describe the average behavior of these decays. The model is brought into a representation that can be compared directly with the golden rule. In this representation, the deviations from exponentiality arise from energy-dependent correlations among the coupling matrix elements that persist even for large systems. Finally, the effects of relaxing the size scaling and “triangle rule” constraints are studied. Sparsity of the random matrix alone is not sufficient to produce slow asymptotic dynamics; both types of constraints are required.

In this article, we describe an analytic approach to the quantum control of wave-packet dynamics. In particular, we show that the field that will produce a specified wave packet in a Rydberg atom can be found approximately from a simple analytic formula. This analytic solution is shown to hold even in the regime of strong excitation, and is found by limiting the duration of the pulsed control field to less than one Kepler period of the system. Comparison with a direct numerical integration of Schrödinger’s equation shows that our solution yields the target state and population transfer with very high fidelity. The possibility of ionization to the continuum is also included in the model. The solution provides some insight into the multiplicity of solutions to the control problem and the relative complexity of the control-field shapes in the weak- and strong-response regimes.

We demonstrate that laser cooling, combined with $V$-scheme optical double-resonance spectroscopy, provides a sensitive means to measure isotope shifts and hyperfine splittings. Our technique is illustrated using the 398.8-nm ${(6s}^2{)}^1{S}_0{-\left(6s6p\right)\mathrm{}}^1{P}_1$ and 555.6-nm ${(6s}^2{)}^1{S}_0{-\left(6s6p\right)\mathrm{}}^3{P}_1$ transitions in a neutral ytterbium atomic beam having natural isotopic composition. With a precision comparable to existing approaches, our unique method has enabled the most complete single-technique survey to date of the ${}^1{S}_0{-}^1{P}_1$ isotope shifts and hyperfine splittings.

We study the dynamic process of splitting a condensate by raising a potential barrier in the center of a harmonic trap. We use a two-mode model to describe the phase coherence between the two halves of the condensate. Furthermore, we explicitly consider the spatial dependence of the mode funtions, which varies depending on the potential barrier. This allows us to get the tunneling coupling between the two wells and the on-site energy as a function of the barrier height. Moreover, we can get some insight into the collective modes that are excited by raising the barrier. We describe the internal and external degrees of freedom by variational ansatz. We distinguish the possible regimes as a function of the characteristic parameters of the problem and identify the adiabaticity conditions.

The high-density Frenkel excitons, which interact with a single-mode cavity field, are investigated in the framework of the q-deformed boson. It is shown that the q-deformed bosonic commutation relations are satisfied naturally by the exciton operators in the high-density limit. An analytical expression of the physical spectra of the excitons is obtained by using the dressed states of the cavity field and the excitons. We also give the numerical study and compare the theoretical results with the experimental results.

We consider a special kind of correlation measurements in single-atom resonance fluorescence, which includes detection of a spectrally filtered photon followed by detection of an unfiltered photon. We relate the stationary normalized intensity correlation function measured in such a scheme to the reduced atomic state following detection of the filtered photon. In the limit of well separated spectral lines of the resonance fluorescence spectrum, we obtain the analytic expression for the reduced atomic state. We show that at resonance excitation, this state is inverted when the filter is tuned in between the central line and any of the sidebands. This effect is interpreted as a result of quantum interference between the complementary atomic radiative transitions giving rise to the detected photon. We propose to observe this effect in measuring the equal-time field correlation function of the filtered and unfiltered photons as a function of the filter resonance frequency.

Lyman-$\alpha$ lines of hydrogenlike ${\mathrm{Ti}}^{21+}$ have been observed with an electron-beam ion trap. The intensity ratio between Lyman-${\alpha }_1$ and -${\alpha }_2$ was measured at electron energies of 10.6, 24.7, and 49.6 keV (2.12, 4.96, and 9.96 in threshold units). The linear polarization of Lyman-${\alpha }_1$ was obtained by comparing the experimental intensity ratio at an observation angle of $90°$ with the total emission cross section ratio calculated by a simple collisional radiative model. The present results are compared with existing theoretical results.

We have measured the yield of metal cluster anions of Al, Co, Ni, and Cu produced in a sputter ion source, and also the distribution of negative fragment ions after collisions in gases of ${\mathrm{H}}_2$ and Xe. For Al and Cu the fragment distributions show pronounced size effects that can be correlated with the stability of the species as reflected in the electron affinity. Modeling the collisional energy transfer, electron emission, and evaporation rates, we find that the fragment abundances are strongly influenced by thermal electron emission. The abundance spectra of the parent ions from the source show a similar correlation with the electron affinity, superimposed on a strong decrease with cluster size. For Co and Ni the negative-ion yields are much smaller than for Al and Cu, both from the source and after fragmentation, and this can be explained by even stronger neutralization by thermal electron emission.

We propose an experiment that permits observation of the de Broglie two-photon wave packet behavior for a pair of photons, using a Mach-Zehnder interferometer. It is based on the use of pulsed lasers to generate pairs of photons via spontaneous parametric down-conversion and the post-selection of events. It differs from previous realizations by the use of a third time-correlated photon to engineer the state of the photons. The same technique can give us which-path information via an “interaction-free” experiment and can be used in other experiments on the foundations of quantum mechanics related to wave-particle duality and to nonlocality.

The moments and correlations of the (classical or quantum) position and momentum variables satisfy a hierarchy of coupled equations, which have been studied and solved numerically for the Hénon-Heiles model. It is found, for chaotic states of the model, that the second moments of the classical and quantum variables grow exponentially at a rate governed by the classical Lyapunov exponent. The differences between quantum and classical variables also grow exponentially, but with a larger exponent. The behavior of this quantum-classical difference exponent is studied in this paper.

It is shown that the energies and the lifetimes of unstable modes of quantum propagation of neutral atoms in a quadrupole magnetic guide can be calculated simply by diagonalizing the complex scaled Hamiltonian. The results reproduce those obtained for the same geometry, but by a different method, by E. A. Hinds and C. Eberlein [Phys. Rev. A 61, 033614 (2000)]. The destabilizing effect of a weak bias magnetic field on the $l=0\mathrm{}$ propagation mode of $s=1/2\mathrm{}$ atoms is illustrated.