We investigate the validity of the Landau-Zener model in describing the output coupling of Bose condensates from magnetic traps by a chirped radio-frequency field. The predictions of the model are compared with the numerical solutions of the Gross-Pitaevskii equation. We find a dependence on the chirp direction and also quantify the role of gravitation.

The polarization-dependent resonance-fluorescence spectra of a bichromatically driven four-level atom are studied. It is shown that very narrow spectral lines can occur in the incoherent part of the spectra for polarization directions that are different from that of the driving field. Squeezing properties of the fluorescent light are also investigated. The degree of squeezing depends on the polarization direction and reaches a maximum of remarkably $56\%.$

I analyze the stimulated emission process in photonic band structures. I consider a dipole transition of a two-level atom which is tuned near an edge of a photonic band gap. I solve numerically the Schrödinger equation for the chosen model without Born and Markovian approximations. It is shown that even one photon in the field can have significant influence on the dynamics of the system providing the atomic transition is tuned near sharp structures of the density of modes.

We describe two-color solitonlike pulses in resonant $\mathsf{V}$-type three-level media with Doppler broadening. We discuss the similarities and differences among our solitons of $\mathsf{V}$-type media and the known solitons of two-level media.

It is argued that the findings of a recent reanalysis by Compagno and Persico [Phys. Rev. A 57, 1595 (1998)] of the Bohr-Rosenfeld procedure for the measurement of a single space-time-averaged component of the electromagnetic field are incorrect when the field measurement time is shorter than that required for light to traverse the measurement’s test body. To this end, the time-averaged “self-force” on the test body, assumed for simplicity to be of a spherical shape, is evaluated in terms of a one-dimensional quadrature for the general trajectory allowed for the test body by Compagno and Persico, and in closed form for the limiting steplike trajectory used by Bohr and Rosenfeld.

We argue that the criticism by Hnizdo [preceding Comment, Phys. Rev. A 60, 4212 (1999)] of the results obtained by Compagno and Persico [Phys. Rev. A 57, 1595 (1998)] on the theory of measurement of the amplitude of the quantum electromagnetic field is unfounded. By a simple and direct approach we show that the quantities evaluated by Hnizdo in his Comment are incorrect and we present the correct results.

By using a complex field with a symmetric combination of electric and magnetic fields, a first-order covariant Lagrangian for Maxwell’s equations is obtained. This leads to a dual-symmetric quantum-field theory with an infinite set of local conservation laws. The dual symmetry is shown to correspond to a helical phase, conjugate to a conserved helicity number.

A scheme for the individual addressing of ions in a trap is described that does not rely on light beams tightly focused onto only one ion. The scheme utilizes ion micromotion that may be induced in a linear trap by dc offset potentials. Thus coupling an individual ion to the globally applied light fields corresponds to a mere switching of voltages on a suitable set of compensation electrodes. The proposed scheme is especially suitable for miniaturized rf (Paul) traps with typical dimensions of about $20-40\hspace{0.5em}\mu \mathrm{m}.$

We present optimal and minimal measurements on identical copies of an unknown state of a quantum bit when the quality of measuring strategies is quantified with the gain of information (Kullback—or mutual information—of probability distributions). We also show that the maximal gain of information occurs, among isotropic priors, when the state is known to be pure. Universality of optimal measurements follows from our results: using the fidelity or the gain of information, two different figures of merits, leads to exactly the same conclusions for isotropic distributions. We finally investigate the optimal capacity of N copies of an unknown state as a quantum channel of information.

An exact formalism for excitation energies of any interacting N-electron system has recently been derived from the linear-response limit of time-dependent Kohn-Sham theory. A response kernel is determined in this theory by the functional derivative of the ground-state Kohn-Sham potential function with respect to electron density. It is shown here that the exchange part of this response kernel is a linear operator determined exactly by the underlying second-quantized Hamiltonian. If correlation response is neglected, the theory reduces to the random-phase approximation including exchange. This formalism justifies methods that combine this exact exchange kernel with density-functional approximations to the correlation kernel.

Accurate relativistic coupled-cluster calculations show that the triply charged species ${\mathrm{HeY}}^{3+}$ is a stable molecule and represents the lightest diatomic trication that does not undergo a Coulomb fragmentation into charged fragments. The diatomic potential-energy curve is approximated by an extended Morse potential, and vibrational-rotational constants for ${\mathrm{HeY}}^{3+}$ are predicted ${(R}_e=224.3\mathrm{}\mathrm{pm},$ $D_0=0.394\mathrm{}\mathrm{eV},$ ${\omega }_e=437\mathrm{}{\mathrm{cm}}^{\mathrm{-}1},$ ${\omega }_e{x}_e=15.8\mathrm{}{\mathrm{cm}}^{\mathrm{-}1},$ $B_e=0.877\mathrm{}{\mathrm{cm}}^{\mathrm{-}1}).\mathrm{}$ It is further shown that the ${\mathrm{He}\mathrm{—}\mathrm{Y}}^{3+}$ bond can basically be described as a charge-induced dipole interaction.

Dielectronic recombination has been investigated for $\Delta n=1\mathrm{}$ resonances of ground-state Li${}^{+}{(1s}^2)$ and for $\Delta n=0\mathrm{}$ resonances of metastable Li${}^{+}\left(1s2s{}^{3}S\right).\mathrm{}$ The ground-state spectrum shows three prominent transitions between 53 and 64 eV, while the metastable spectrum exhibits many transitions with energies $<3.2\mathrm{}$ eV. Reasonably good agreement of R-matrix, $\mathrm{LS}$ coupling calculations with the measured recombination rate coefficient is obtained. The time dependence of the recombination rate yields a radiative lifetime of $52.2\pm 5.0$ s for the 2${}^{3}S$ level of Li${}^{+}.$

A ${}^3{\mathrm{He}}^{+}$ beam with nuclear polarization was produced by passing a fast ${}^3{\mathrm{He}}^{+}$-ion beam through a thick polarized Rb vapor target in a strong magnetic field. Observed polarization transfer coefficients as a function of the Rb vapor thickness are qualitatively explained by an electron pumping model based on multiple processes of electron capture and stripping. The experimentally obtained polarization and beam current for the ${}^3{\mathrm{He}}^{+}$ beam were, respectively, 0.07 and 2 $\mu \mathrm{A}$ for a Rb polarization of 0.2.

I report the ratio of multiple-to-single photoionization of ground-state lithium at the high-energy limit, using fully correlated variational wave functions in Hylleraas coordinates. The reported ratio, which is essentially the ratio of double-to-single ionization, is $0.0336087\left(5\right).$ The calculation is also extended to other states of Li as well as to the ground state of ${\mathrm{Be}}^{+}.$

Dissociative recombination of a doubly charged molecular ion ${\mathrm{CO}}^{2+}$ has been studied, using a heavy-ion storage ring. There are two final channels of this reaction $({\mathrm{C}\mathrm{}+\mathrm{}\mathrm{O}}^{+}$ and ${\mathrm{O}\mathrm{}+\mathrm{}\mathrm{C}}^{+})$ that were found to be of about equal strength up to an energy of about 2 eV. The total recombination cross section (yielding C or O) is found to be $\sigma =[2.2/E(\mathrm{eV}\left)\right]\times {10}^{-16}{\mathrm{cm}}^2$ for $E<~1$ eV, where E is the electron energy. This indicates that the recombination is of the direct type with a curve crossing between the initial state and some repulsive curve of the singly charged ion. Within an accuracy of a factor of 2 we obtain a total recombination rate coefficient $\alpha =0.9\mathrm{}\times {10}^{-7}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ at $T=300\mathrm{}$ K that is comparable to that of ${\mathrm{CO}}^{+}.$

We describe a comprehensive investigation of trap loss in a two-species Na-Cs magneto-optical trap. Observed losses, due to the interspecies interactions, are attributed to collisions in which a change in the fine-structure state of the Na partner causes the escape of atoms from the trap. Results are described in terms of the heteronuclear pair potentials and the interaction of the colliding pairs with the radiatively active environment.

${\mathrm{CS}}_2$ is identified as a molecule for which distinction can be made between dynamic and geometric alignment induced by intense laser fields. Measured anisotropic angular distributions of fragment ions arise from (i) dynamic alignment of the S-C-S axes along the laser polarization vector for 35-ps laser pulses and (ii) geometric alignment due to an angle-dependent ionization rate in the case of 100-fs pulses. Results of classical calculations of the alignment dynamics support our observations. By comparing mass spectra obtained with linearly and circularly polarized light it is not possible to distinguish between dynamic and geometric alignment.

We report laser cooling of fermionic ${}^{40}\mathrm{K}$ atoms, with temperatures down to $(15\mathrm{}\pm 5)\hspace{0.5em}\mu \mathrm{K},$ for an enriched sample trapped in a magneto-optical trap and additionaly cooled in optical molasses. This temperature is a factor of 10 below the Doppler-cooling limit and corresponds to an rms velocity within a factor of 2 of the lowest realizable rms velocity $\left(\sim {3.5v}_{\mathrm{rec}}\right)$ in three-dimensional optical molasses. Realization of such low atom temperatures, up to now only accessible with evaporative cooling techniques, is an important precursor to producing a degenerate Fermi gas of ${}^{40}\mathrm{K}$ atoms.

In this Rapid Communication we report on the autoionization dynamics of the $5d7d$ doubly excited state in barium in a static electric field. The different experiments and theory show Stark beatings in the autoionization process. Also it appears that the total spin of the two valence electrons plays a major role in the ionization dynamics. Absorption spectroscopy revealed the ionization dynamics near the core, while an atomic streak camera was used to record the time-dependent electron emission, probing the wave function when it is far from the core. Calculations based on multichannel quantum defect theory are compared to experimental data and we are able to predict the singlet-triplet mixing.