Wavelengths of the fine-structure transition $2s{}^2{S}_{1/2}$–$2p{}^2{P}_{1/2}$ in lithiumlike ${\mathrm{Sn}}^{47+}$ and ${\mathrm{Xe}}^{51+}$ have been determined using beam foil excitation and grazing incidence spectroscopy. Transition wavelengths of $114.895\pm 0.008\hspace{0.5em}\AA$ for ${\mathrm{Sn}}^{47+}$ and $103.475\pm 0.007\hspace{0.5em}\AA$ for ${\mathrm{Xe}}^{51+}$ have been measured. While there has been no previous measurement of this transition in Sn, the Xe result marks an improvement in accuracy of more than an order of magnitude compared with previous experiments. The achieved precision of 70 ppm for the 1/2-1/2 transition allows for a 0.1% QED test which establishes a new benchmark for Li-like ions in the medium Z range. The experimental uncertainty is smaller than the size of the smallest calculated contribution to the transition energy.

With the Solar Ultraviolet Measurements of Emitted Radiation instrument—a high-resolution normal-incidence telescope and spectrometer on board the Solar and Heliospheric Observatory—heliumlike $1s2s{}^3{S}_1–1s2p{}^3{P}_{0,2}$ transitions in the highly ionized species ${\mathrm{Ne}}^{8+},{\mathrm{}\mathrm{Na}}^{9+},{\mathrm{}\mathrm{Mg}}^{10+},$ and ${\mathrm{Si}}^{12+}$ were observed. The spectral lines were emitted by high-temperature solar flare plasmas. In this paper, we report on wavelength measurements of the He-like lines identified in the recorded spectra. The wavelength uncertainties we obtained from the solar measurements are $<~20\mathrm{m}\AA \left(1\mathrm{}\sigma \right),$ and in one case $<~30\mathrm{m}\AA .$ This is comparable to or better than the best determinations so far achieved for these heliumlike $1s2s{}^3{S}_1–1s2p{}^3{P}_{0,2}$ transitions with instrumentation in the laboratory. For the ${\mathrm{Na}}^{9+}{}^3{S}_1{–}^3{P}_2$ transition we report what is to our knowledge the first wavelength measurement. The knowledge of the accurate wavelengths can provide important checks on atomic structure calculations.

Single ionization total cross sections for proton impact on ${\mathrm{N}}_2,$ CO, ${\mathrm{CH}}_4,$ and ${\mathrm{CO}}_2$ are calculated by applying the continuum-distorted-wave-eikonal-initial-state model. Two different approximations have been considered for molecular targets: Bragg’s additivity rule and a molecular representation of the bound state target wave function. In the latter, the cross section is approximated by a linear combination of atomic cross sections where the coefficients are determined from a population analysis and the binding energies have been extracted from experimental spectra. The results from both models are compared with experimental data.

Doubly differential cross sections for inclusive single-electron emission in $3.6\hspace{0.5em}{\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{a}\mathrm{m}\mathrm{u}\mathrm{}\mathrm{Au}}^{53+}+\mathrm{Ar}$ collisions are calculated in the continuum distorted wave with eikonal initial-state approximation. Previously observed structures in the low-energy continuum are traced back to a known deficiency of the Hartree-Fock-Slater target potential that has been used in the work [R. Moshammer et al., Phys. Rev. Lett. 83, 4721 (1999)]. The structures do not occur, if the argon atom is described in terms of the optimized potential method, in which the electronic exchange interaction is treated exactly.

We calculate the scattering states and cross sections for a Bose-Einstein condensed dilute gas trapped in a spherical square well of finite depth. The interactions are treated in the scattering length approximation. We solve the Gross-Pitaevskii equation and the Bogoliubov equations for bound and scattering states. The results show that there are transparency effects reminiscent of those conjectured to occur for strongly coupled systems. When incident particle wavelengths $\lambda$ are comparable to the well size a, exchange induced transparency enhancement is dramatic only for particular combinations of well depth, interaction strength, and particle number. For particles with large momenta $(a/\lambda \gg 1),$ however, exchange with the condensate results in enhanced transmission for all coupling strengths. We calculated the rate of decay of the scattering states to leading order in anharmonic corrections to the Bogoliubov approximation and found the corresponding inelastic cross sections to be extremely small.

We have performed an experiment to measure the angular distribution of quasi-elastic scattering of the noble-gas ions ${\mathrm{He}}^{+},$ ${\mathrm{Ne}}^{+},$ ${\mathrm{Ar}}^{+},$ and ${\mathrm{Xe}}^{+}$ with an individual carbon atom in a ${\mathrm{C}}_{60}$ molecule at incident energies up to 10 keV. The measured differential cross sections have shown an anomalously strong screening effect compared with those in the case of scattering on an isolated carbon atom. Effective interatomic potentials have been evaluated numerically from the measured cross sections. They were found to be modeled well by a Moliére screening potential, but strongly modified by an additional screening function represented by a simple Woods-Saxon-type function.

We discuss the propagation of wave packets through interacting environments. Such environments generally modify the dispersion relation or shape of the wave function. To study such effects in detail, we define the distribution function $P_X\mathrm{}\left(T\right),$ which describes the arrival time T of a packet at a detector located at point X. We calculate $P_X\mathrm{}\left(T\right)\mathrm{}$ for wave packets traveling through a tunneling barrier and find that our results actually explain recent experiments. We compare our results with Nelson’s stochastic interpretation of quantum mechanics and resolve a paradox previously apparent in Nelson’s viewpoint about the tunneling time.

Full-potential linear-muffin-tin-orbital molecular-dynamics calculations have been performed to investigate the structures and energies of ${\mathrm{Si}}_{20}$ clusters. Among the selected 15 stable structures for ${\mathrm{Si}}_{20},$ the most stable structure is constructed by stacking ${\mathrm{Si}}_9$ tricapped trigonal prisms (TTP) subunits. Its symmetry is $C_2.$ Another structure with almost the same binding energy as the ground-state structure is also obtained by stacking ${\mathrm{Si}}_9$ tricapped trigonal prisms subunits, but its symmetry is $D_{3h}.$ The subunit is just the ground-state structure of ${\mathrm{Si}}_{10},$ with $C_{3v}$ symmetry. The ground-state structure of ${\mathrm{Si}}_{20}$ can interpret the fragmentation experimental result and the absorption property of ammonia molecules for ${\mathrm{Si}}_{20}^{+}.$

We report the integral elastic cross section for low-energy electron scattering by the boron trihalides ${\mathrm{BCl}}_3,$ ${\mathrm{BBr}}_3,$ and ${\mathrm{BI}}_3.$ To perform our calculations, we employed the Schwinger multichannel method with pseudopotentials. We have focused our attention only in the $B_2$ irreducible representation, where we found shape resonances for the three molecules in a previous static-exchange calculation, at energies below 5 eV. We included polarization effects to improve the description of the resonances and found that only the resonance for ${\mathrm{BCl}}_3$ remains. For ${\mathrm{BBr}}_3$ and ${\mathrm{BI}}_3,$ the resonances become bound states.

Wave-packet methods involving the numerical solution of the time-dependent Schrödinger equation have been used with great success in the calculation of cross sections for dissociative recombination of molecular ions by electron impact in the high energy region where the “boomerang” model [L. Dube and A. Herzenberg, Phys. Rev. A 11, 1314 (1975)] is valid. We extend this method to study low-energy dissociative recombination where this approximation is no longer appropriate. We apply the method to the “direct” low-energy dissociative recombination of ${\mathrm{HD}}^{+}.$ Our results are in excellent agreement with calculations using the multichannel quantum defect method.

For the case of an atomic Bose-Einstein condensate formed in a symmetrical double-well potential with well-separated minima, the dynamics of Bose-condensed atoms interacting with a single-mode quantized traveling-wave laser field are investigated in detail. By considering the system consisting of the Bose-condensed atoms and laser field with and without dissipation, the eigenstates and eigenvalues of the corresponding Hamiltonian for both cases are obtained. The time development of the Bose-condensed state plays a major role in the discussion. It is shown that the probability of finding all atoms in the Bose-condensed state displays an undamped oscillatory behavior in the absence of dissipation and a damped oscillatory behavior in the presence of dissipation. Moreover, it is found that the tunneling effect can increase the oscillatory frequency among the dressed bosonic states and affect the dynamics of the system. As an application of these results, a characteristic time that may be used to evaluate the number of condensed atoms is introduced.

The nonlinear propagation of few-optical-cycle pulses through a dispersive Kerr medium, as, e.g., fused silica, is studied theoretically using a global approach to dispersion without applying the slowly varying envelope approximation. Contrary to amplitude self-steepening, a nearly triangular pulse shape with the steep side on the leading front is predicted. The calculation of the ultrawide spectrum and the spectral phases demonstrates that half-cycle pulses with a full width at half maximum as short as 0.5 fs and single-cycle pulses can be generated by the application of an appropriate broadband modulator for the compensation of the frequency-depending phase.

Light experiences dielectric matter as an effective gravitational field and matter experiences light as a form of gravity as well. Light and matter waves experience each other as dual space-time metrics, thus establishing a unique model in field theory. Actio et reactio are governed by Abraham’s energy-momentum tensor and equations of state for quantum dielectrics.

Frustrated total internal reflection is considered as the classical analog of quantum-mechanical tunneling. Here the tunneling time in frustrated total internal reflection is discussed. It is shown that the phase time allows for vanishing and negative barrier traversal times. The tunneling time is shown to be dominated by a time scale based on the Goos-Hänchen shift. The role of further nonspecular deformations of the transmitted beam is addressed. The resulting tunneling times are compared with experimental data.

We show how an interaction with the environment can enhance fidelity of quantum teleportation. To this end, we present examples of states which cannot be made useful for teleportation by any local unitary transformations; nevertheless, after being subjected to a dissipative interaction with the local environment, the states allow for teleportation with genuinely quantum fidelity. The surprising fact here is that the necessary interaction does not require any intelligent action from the parties sharing the states. In passing, we produce some general results regarding optimization of teleportation fidelity by local action. We show that bistochastic processes cannot improve fidelity of two-qubit states. We also show that in order to have their fidelity improvable by a local process, the bipartite states must violate the so-called reduction criterion of separability.

Quantum-mechanical complementarity ensures the security of the key-distribution scheme reported by Brassard and Bennet in 1984 (BB84), but does not prohibit use of multi-photons as a signal carrier. We describe a novel BB84 scheme in which two nearly orthogonal coherent states carry the key, and the superposition of these states (cat states) protects the communication channel from eavesdropping. Information leakage to eavesdroppers can be determined from the visibility of the interferential fringes in the distribution of the outcome when a certain quadrature component is measured through homodyne detection. The effect of channel loss and detector inefficiency is discussed.

We study the amount of classical communication needed for distributed quantum-information processing. In particular, we introduce the concept of “remote preparation” of a quantum state. Given an ensemble of states, Alice’s task is to help Bob in a distant laboratory to prepare a state of her choice. We find several examples of an ensemble with an entropy S where the remote preparation can be done with a communication cost lower than the amount $\mathrm{}\left(2S\right)\mathrm{}$ required by standard teleportation. We conjecture that, for an arbitrary N-dimensional pure state, its remote preparation requires $2{\log }_{2}N$ bits of classical communication, as in standard teleportation.

High-resolution spectra of complex atoms and molecules have been described efficiently in the energy domain using quantum-defect methods. At the same time, the coarser modulations in energy associated with external field effects such as quasi-Landau phenomena have been most fruitfully described in the framework of semiclassical closed-orbit theory, which relates the short-time quantum-mechanical behavior to the classical orbits of the system. In this paper, we demonstrate a unified theory based on semiclassical scattering matrices that adds to the power and generality of both methodologies.

We derive general relationships of the S matrix of fields containing evanescent components. Our formalism covers time-independent quantum scattering as well as scattering of classical scalar waves. We show that reciprocity, energy (or probability) conservation, and time-reversal symmetry in the presence of evanescent waves lead to relationships that extend the well-known relations previously derived in asymptotic scattering. On this basis, we discuss the link between reciprocity and time-reversal symmetry. We also address the experimental feasibility of time reversal of a field containing evanescent components.

Protons with energies in the keV domain are scattered from a clean and flat LiF(001) surface under a grazing angle of incidence. For specific projectile energies, the periodic Coulomb field owing to the point-charge lattice of the ionic crystal leads to the “resonant coherent excitation” (RCE) of the $n=1\mathrm{}$ to the $n=2\mathrm{}$ states. This excitation is probed in our experiments via the intensity of Lyman-α light, emitted in the radiative decay of the excited states, as a function of projectile energy and azimuthal orientation of the crystal surface. We find clear evidence for RCE with a good signal to background ratio that allows us to perform detailed studies on the position, width, and line shape of the resonance.