A method of sideband Raman cooling to the vibrational ground state of the $m=0\mathrm{}$ Zeeman sublevel in a far-detuned two-dimensional optical lattice is proposed. In our scheme, the Raman coupling between vibrational manifolds of the adjacent Zeeman sublevels is shifted to the red sideband due to the ac Stark effect induced by a weak pump field. Thus cooling and optical pumping to $m=0\mathrm{}$ are achieved by purely optical means with coplanar cw laser beams. The optical lattice and cooling parameters are estimated in the framework of simple theoretical models. An application of the transverse sideband cooling method to frequency standards is discussed. Coherent population trapping for the sideband Raman transitions between the degenerate vibrational levels is predicted.

We report the observation of the predicted metastable ${4p}^3{}^{4}S$ state in the ${\mathrm{Ca}}^{\mathrm{-}}$ ion utilizing a spectroscopic technique based on nonlinear resonant multicolor absorption via an autodetaching state. The binding energy of the ${}^{4}S$ state is determined to be 586.86(10) meV with respect to the parent $\mathrm{Ca}{(4p}^2{}^{3}P)$ state, a value less than 3 meV from the predicted one. The lifetime of the ${}^{4}S$ state is determined to be larger than 7 ps.

We propose and analyze an approach to convert an atomic condensate into a condensate of diatomic molecules in the rovibrational ground state. The process consists of a stimulated Raman transition dramatically enhanced by a time-dependent magnetic field that sweeps over a field-induced Feshbach resonance. For Na atoms the Raman transition probability is enhanced by seven orders of magnitude, leading to a conversion efficiency of up to 20%. The resulting condensate is expected to be as stable as the present atomic condensates. The approach shows promise as a more general process for Feshbach engineering molecular condensates from condensates of the constituent atoms/molecules.

The widely used assumption that transitions induced by slowly changing perturbations are completely described by the topology of adiabatic energy surfaces in the plane of a complex perturbation parameter is reexamined. This assumption is the basis for the hidden crossings theory and most two-state models and yields an exponential decrease of transition probabilities and cross sections with decreasing speed of the perturbation $v.\mathrm{}$ We show that for a large class of problems, these approximations do not describe correctly transitions in the adiabatic limit. Contributions neglected lead, instead, to dominant power-law dependences in inelastic collisional cross sections, $\sigma \propto v^4.$ We illustrate the interplay between different contributions for a collisional model system for which exact transition probabilities can be determined.

We offer an improved method for using a nuclear-magnetic-resonance quantum computer (NMRQC) to solve the Deutsch-Jozsa problem. Two known obstacles to the application of the NMRQC are an exponential diminishment of density-matrix elements with the number of bits, threatening weak signal levels; and the high cost of preparing a suitable starting state. A third obstacle is a heretofore unnoticed restriction on measurement operators available for use by a NMRQC. Variations on the function classes of the Deutsch-Jozsa problem are introduced, both to extend the range of problems advantageous for quantum computation and to escape all three obstacles to the use of a NMRQC. At the cost of an extra work bit and a polynomial increase in the number of gate operations required, the method solves the Deutsch-Jozsa problem while avoiding an exponential loss of the signal, preparation of a pseudopure state, and temporal averaging.

Relativistic configuration-interaction (RCI) calculations with $\sim 15000$ vectors have been done for f values, Landé g values, and hyperfine structure constants for Fe V. There is at least a factor of 2 improvement over our earlier achievable accuracies (Nb II). The 21 largest f values $\mathrm{}(>0.01\mathrm{})\mathrm{}$ have an average length-velocity gauge difference of 6.7%, and the average error in the energy differences between adjacent levels is 213 (180) ${\mathrm{cm}}^{\mathrm{-}1}$ for even- (odd-) parity levels. We find significant f value differences as compared to recent values from Breit-Pauli R-matrix calculations, and, to a lesser extent, as compared to older semiempirical f values. Oscillator strengths to three nearly degenerate odd-parity levels are sensitive to errors smaller than 200 ${\mathrm{cm}}^{\mathrm{-}1},$ but the sum is conserved, as expected.

The correspondence between intense ion-induced and laser-induced fields is explored in terms of magnitude and the temporal, directional, and spatial properties of the two types of field. Irradiation of benzene by these fields yields similar ionization patterns, indicating that whether the intense field is of picosecond or attosecond duration is of little consequence to the ionization dynamics.

A simple analytic form is presented for the full velocity–angular-momentum distribution function for gas-phase linear ions drifting in an atomic bath gas under a constant external electric field. Predictions of temperatures, drift velocities, and alignment parameters from this form are compared in detail against molecular-dynamics calculations for ${\mathrm{NO}}^{+}$ drifting in helium. The form is accurate, compact, and based upon a physically motivated expansion. In essence, simple Maxwellian-like functions are generalized by allowing appropriate temperatures to become functions of velocity and rotational angular momentum. Over a wide range of reduced field strengths, including the equilibrium state, this form is able to account accurately for many properties at a microscopic level with only a few adjustable parameters.

Effects of intermediate coupling and configuration interaction on the partial transition rates, total decay widths, and angular distribution parameters of the Ar resonant Auger transitions ${2p}^{5}4\overrightarrow{s}{3s}^1{3p}^{5}4s$ and of the second-step Auger transitions ${3s}^1{3p}^5{4s(}^2{P}_{1/2,3/2})\to {3p}^4$ have been studied both theoretically and experimentally. Transition rates and angular anisotropies have been calculated for the first- and second-step transitions using the multiconfiguration Dirac-Fock method. High-resolution spectra of both steps have been measured and used to test different schemes for the description of the many-particle states and the existence of possible coherence effects in the second-step spectra.

Absolute total one- and two-electron-transfer cross sections for ${\mathrm{O}}^{q+}$ $\mathrm{}(q=3,2\mathrm{})\mathrm{}$ with CO were measured at $\sim 1.5q$ keV energies. The measurement was carried out by a technique that combines a laser ablation ion source and a reflection time-of-flight mass spectrometer. The single- and double-electron capture cross sections for ${\mathrm{O}}^{3+}$ with CO are $(1.26\mathrm{}\pm 0.18)\times {10}^{-15}$ and $(0.72\mathrm{}\pm 0.11)\times {10}^{-15}$ ${\mathrm{cm}}^2,$ respectively. The single-electron capture cross section for ${\mathrm{O}}^{2+}$ with CO is $(0.76\mathrm{}\pm 0.11)\times {10}^{-15}$ ${\mathrm{cm}}^2.$

Semiclassical ab initio values of oxygen-broadened and air-broadened NO infrared linewidths are reported in the range of atmospheric temperatures 163–299 K. The calculation is based on the authors’ recently developed extended exact trajectory approach implemented within the Robert-Bonamy formalism for collisional line broadening. The results obtained are found to be in excellent agreement with recent straightforward measurements.

We propose to measure the electron’s permanent electric dipole moment (EDM) using cesium atoms trapped in a sparsely populated, trichromatic, far blue-detuned three-dimensional (3D) optical lattice. In the proposed configuration, the atoms can be strongly localized near the nodes of the light field and isolated from each other, leading to a strong suppression of the detrimental effects of atom-atom and atom-field interactions. Three linearly polarized standing waves with different frequencies create an effectively linearly polarized 3D optical lattice and lead to a strong reduction of the tensor light shift, which remains a potential source of systematic error. Other systematics concerning external field instability and gradients and higher-order polarizabilities are discussed. Furthermore, auxiliary atoms can be loaded into the same lattices as effective “comagnetometers” to monitor various systematic effects, including magnetic-field fluctuations and imperfect electric-field reversal. We estimate that a sensitivity 100 times higher than the current upper bound for the electron’s EDM of $4\times {10}^{-27}e\mathrm{cm}$ can be achieved with the proposed technique.

Bose-Einstein condensates with attractive interatomic interactions undergo collective collapse beyond a critical number. We show theoretically that if the low-lying collective modes of the condensate are excited, the radial breathing mode further destabilizes the condensate. Remarkably, excitation of the quadrupolar surface mode causes the condensate to become more stable, imparting quasiangular momentum to it. A significantly larger number of atoms may then occupy the condensate. Efforts are under way for the experimental realization of these effects.

We report on a demonstration of x-ray-ultraviolet amplification following collisional excitation in a discharge-created plasma waveguide irradiated by a picosecond optical laser pulse. A capillary discharge was used to generate a sulfur plasma column with a large concentration of Ne-like ions and a radially concave electron density profile. The intense short laser pulse rapidly heated the electrons, producing amplification in the $3p{}^1{S}_0–3s{}^1{P}_1$ transition of Ne-like S at 60.8 nm. The integrated gain-length product obtained exciting a 3-cm-long capillary with a 0.46-J short laser pulse is 6.8. The beam divergence was observed to decrease as a function of plasma column length, reaching 2.5 mrad for 30-mm-long capillaries. This hybrid laser pumping scheme could lead to a new generation of efficient tabletop soft-x-ray lasers.

Electromagnetically induced transparency (EIT) has been studied primarily within the context of multilevel atomic systems. We show that EIT can occur also in a two-level atomic system and can lead to strong self-action and slow-light effects that are not hampered by material absorption, with important potential implications for processes such as squeezed-light generation and the propagation of optical solitons.

An experimental comparison of phase conjugate feedback to conventional optical feedback in a semiconductor laser is presented, which contrasts the optical frequency spectra and power noise spectra with varying levels of feedback. These spectra are correlated with the single frequency regimes III and V and the chaotically unstable regime IV. Conventional feedback is derived from a mirror and variable neutral density filter, and the phase conjugate feedback is derived from a self-pumped rhodium doped barium titanate photorefractive crystal. Both systems show two stable, single frequency operation regions analogous to regime III and V operation separated by a single region of unstable operation analogous to regime IV. It is found that phase conjugate feedback leads to distinctive behaviors including: differences in the relative intensity noise spectra; dynamically varying output frequency spectra close to the transition from regime IV to V; systematic power transfer from one laser diode longitudinal mode to a nearest neighbor through regime IV; and a very much larger range of feedback levels leading to unstable output. The level of optical feedback leading to a transition from regime III to IV is the same for conventional optical feedback and phase conjugate feedback when the correction for the different coupling efficiencies is made. The transition from regime IV to V occurs for much higher levels of feedback when PCF is used leading to the larger range of feedback levels giving chaotic behavior with PCF. The results are discussed in the context of existing theoretical models of laser diodes with phase conjugate feedback.

Electroproduction of relativistic positronium may be of importance for obtaining beams of polarized or unpolarized positronium. We give cross sections for singlet and triplet positronium production in high-energy collisions of electrons on atoms, correct to all orders in the atomic number Z, including a complete description of atomic screening, using the Thomas-Fermi-Molière atomic model. The results are analogous to the photoproduction cross section results recently published [Phys. Rev. A 60, 1883 (1999)]. However, since in electroproduction the positronum is produced as a spectrum with spectral distributions varying considerably according to the spin of the positronium, singlet or triplet, the resulting cross sections are strongly dependent on screening, more so than in photoproduction. We show that with initially longitudinaly polarized electrons, polarization may be transferred to the positronium, so that beams of sizably polarized positronium may be obtained.

The emergence of decoherence in quantum electrodynamics is investigated. On combining superoperator methods with functional techniques from field theory, the degrees of freedom of a thermal radiation field are eliminated and the influence phase functional is derived which governs the reduced dynamics of the matter variables. Employing a prototypical interference device, a decoherence functional is developed which provides a gauge invariant relativistic measure for the degree of decoherence. It is demonstrated that the decoherence functional describes the destruction of quantum coherence through the emission of bremsstrahlung which is caused by the relative motion of the interfering components of a superposition. Explicit analytical expressions for the vacuum and the thermal contribution to the decoherence functional and for the corresponding coherence lengths are determined. These expressions reveal that bremsstrahlung leads to a fundamental decoherence mechanism which dominates for short times and which is present even in the electromagnetic field vacuum at zero temperature. The influence of bremsstrahlung on the center of mass coordinate of a system of many identical charged particles is also studied and is shown to lead to a strong suppression of quantum coherence.

The phase estimation algorithm is so named because it allows an estimation of the eigenvalues associated with an operator. However, it has been proposed that the algorithm can also be used to generate eigenstates. Here we extend this proposal for small quantum systems, identifying the conditions under which the phase-estimation algorithm can successfully generate eigenstates. We then propose an implementation scheme based on an ion trap quantum computer. This scheme allows us to illustrate two simple examples, one in which the algorithm effectively generates eigenstates, and one in which it does not.

We report absolute cross sections for binary encounter and convoy electron emission. Fast-electron velocity spectra were measured for atomic collisions induced by a 45 MeV/u ${}^{58}\mathrm{Ni}$ beam impinging on solid targets by means of the multidetector ARGOS in a large angular range (from 1.5° to 165°). Different conducting elemental targets ${(}^{12}\mathrm{C},$ ${}^{27}\mathrm{Al},$ ${}^{58}\mathrm{Ni}$ and ${}^{64}\mathrm{Ni},$ ${}^{\mathrm{nat}}\mathrm{Ag},$ ${}^{197}\mathrm{Au})$ and polystyrene were used. Characteristics of electrons with a velocity close to the beam velocity (convoy electrons) were found to be very sensitive to the incoming charge state of the projectile. Their yield increases with the target atomic number. The yield of binary encounter electrons with a velocity of almost twice the beam velocity at small ejection angles is roughly proportional to the area density of encountered target electrons. The velocity spectra centroids of these electrons are shifted towards lower velocities than predicted by simple two-body relativistic kinematics. Surprisingly, this effect seems to be mostly independent of target material and thickness. With increasing target atomic number, the high-energy tails of the spectra exhibit an unexpectedly large number of very fast electrons. A multiple-scattering mechanism involving multiple collision sequences of electrons between projectile and target atoms is invoked to explain this effect. The data also show evidence for an excess of fast electrons in the backward direction.