In chaotic ionization of the classical s-wave model of two-electron atoms, initial conditions of bound nonionizing trajectories form Cantor sets in phase space. The fractal dimensions of these sets are noninteger and increase with increasing nuclear charge, i.e., with decreasing importance of the electron-electron interaction.

We study the coherent scattering of weak near-resonant light off a Bose-Einstein condensate formed by a system of cooled atoms in a trap. Scattering occurs primarily in the forward direction, and exhibits a very narrow feature on top of a broad non-Lorentzian background.

We have measured strongly negative β values of the 3s-participator lines at the magnesium 2p→4s and 2${\mathit{p}}_{1/2}$→3d excitations. Observed β values of the spectator lines following 2p→4s excitation are not reproduced by the strict spectator model. Our multiconfiguration Dirac-Fock calculations show that the resonant Auger spectra are influenced by unusually pronounced configuration interaction in the excited state. This influence is strongly enhanced by a change of sign in the Auger amplitude of the leading term near the transition energy, a dynamic effect similar to a Cooper minimum in photoionization.

The eigenchannel R-matrix method for single photoionization is extended to describe a class of two-electron escape processes. We apply this approach to calculate the double photoionization of helium by single-photon absorption for photon energies in the range 80–280 eV. Pseudoresonances in the double continuum are eliminated by performing a Gailitis average and by averaging the final spectrum over the size of the R-matrix box. Calculations are presented in both the velocity and acceleration gauges. The ratio of double- and single-photoionization cross sections, a key parameter for characterizing electron correlations, is compared to existing theoretical and experimental values.

The formation of atom-optical gratings induced by multiphoton excitation of Rydberg states is discussed for fast atoms. With the help of semiclassical path-integral methods the correlation between the dynamics of a laser-excited Rydberg electron and the momentum transferred to the atomic center of mass in a spatially modulated laser field is exhibited quantitatively. These types of laser excitation processes might offer new perspectives for the realization of atomic multiple beam splitters and for atom-lithographic applications.

We demonstrate enhanced loading of a ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ magneto-optic trap by broadening the frequency spectrum of the laser trapping light with a resonant electro-optic modulator. We achieve an ∼20-fold improvement in the loading rate over that obtained without a broadened spectrum when directly capturing atoms from a divergent atomic beam.

The strong ellipticity dependence of correlated two-electron multiphoton ionization of neon and of the high-harmonic emission from argon (harmonic N=21) and neon (N=41) are reported. These measurements suggest a common underlying mechanism and are quantitatively consistent with a recently developed Keldysh-like model of high harmonic generation which treats the interaction between a newly freed electron and the ion core.

We propose a technique to generate nonclassical vibrational states of the quantized center-of-mass motion of an ion in a harmonic trap, based on the quantum conversion between the quantum cavity field and the quantized center-of-mass motion. It is shown that when an ion trap system interacts with the eigenmode of a single-mode Fabry-Pérot cavity, where the trap is set in, and with an external classical driving electromagnetic field through Raman transitions, the interchange of the quantum features between the quantum cavity field and the quantized trap occurs. This kind of quantum conversion can be used to prepare some nonclassical trap states for the ion trap as well as to measure the quantum statistics of an initial nonclassical vibrational state.

The decay characteristics of two-state Rydberg atoms are investigated in a microwave cavity driven simultaneously by two strong rf fields. Tuning one of the driving fields leads to sharp resonances in the decay rate of the upper atomic level. Their width may become smaller than the cavity linewidth and transit time broadening. We present a theoretical model, interpreting the resonances as cavity-induced decay of Floquet states of the composite atom-field system. The observed phenomena arise from the interplay of cavity-modified Bloch-Siegert shifts and dynamic enhancement of spontaneous emission at single-photon and multiphoton resonances.

We have demonstrated an order of magnitude increase in the number and in the lifetime of magneto-optically trapped ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ atoms collected from a low-pressure vapor. The improvement results from the reduction of light-assisted collision losses and is achieved by shelving the atomic population into the lower hyperfine ground state. Large fractional populations of the lower hyperfine ground state have been obtained by blocking the hyperfine repumping light in the region of the trapped atoms and by application of laser light that optically pumps the atoms into that state. We have observed trap lifetimes in excess of 700 s at our highest vacuum levels. At the rubidium pressure that maximizes the product of the number and lifetime of trapped atoms we observe a lifetime of 240 s with 5×${10}^7$ trapped atoms, under conditions for which an ordinary magneto-optical trap has a lifetime of only 14 s with 3×${10}^6$ atoms.

Laser patterns in the plane transverse to the beam propagation direction are investigated. We find a lasing state, alternating standing waves, which consists of two perpendicularly oriented, out-of-phase standing waves in the transverse plane. This state is stable near threshold and gives rise to square intensity patterns. Numerical simulation on the laser equations has been carried out and the effect of transverse boundaries on wave patterns is addressed.

A degenerate beam of down-converted photon pairs from a nonlinear crystal pumped by pulsed light was mixed with coherent local oscillator pulses by a beam splitter, and the coincidence rate for detections of photons at the two output beams was measured. The coincidence rate showed interference fringes as the phase difference between the pump light and the local oscillator was varied. It showed a negative correlation in some range of the phase difference.

Solutions of Schrödinger’s equation for systems interacting with long-range power-law potentials, ${\mathit{V}}_{\mathrm{int}}$(r)∝${\mathit{r}}^{\mathrm{-}\mathit{n}}$ with n≥2, are cast in the form of a power series in ${\mathit{V}}_{\mathrm{int}}$. These perturbations lead to secular divergences that are eliminated by renormalizing the angular-momentum quantum number. Long-known perturbation techniques in classical mechanics and quantum-field theory yield modified effective-range formulas, quantum-defect functions, and solutions of close-coupling equations for wave propagation in long-range fields. As an example, we extract in first-order perturbation theory a modified effective-range expansion for the phase shift of an electron interacting with an atomic 1/${\mathit{r}}^4$ polarization potential. Near thresholds, the method is applicable to all power-law potentials with n≥2, and to their combinations, as well as to multichannel problems involving anisotropic potentials.

Approximate formulas are given for the effective Hamiltonian ${\mathit{H}}_{\mathrm{\parallel }}$(t) governing the time evolution in a subspace ${\mathit{scrH}}_{\mathrm{\parallel }}$ of the state space scrH. It is proved that this approximation is correct for any Hamiltonian H of the system under consideration at the early-time period. The approximate form of the survival amplitude for a given state improving Fleming’s estimation in the short-time region is found and the properties of a decay rate for small, intermediate, and long times are discussed.

The classical limit of quantum mechanics is usually discussed in terms of Ehrenfest’s theorem, which states that, for a sufficiently narrow wave packet, the mean position in the quantum state will follow a classical trajectory. We show, however, that that criterion is neither necessary nor sufficient to identify the classical regime. Generally speaking, the classical limit of a quantum state is not a single classical orbit, but an ensemble of orbits. The failure of the mean position in the quantum state to follow a classical orbit often merely reflects the fact that the centroid of a classical ensemble need not follow a classical orbit. A quantum state may behave essentially classically, even when Ehrenfest’s theorem does not apply, if it yields agreement with the results calculated from the Liouville equation for a classical ensemble. We illustrate this fact with examples that include both regular and chaotic classical motions.

The question as to whether neutron acceleration can occur in uniform electromagnetic fields is examined. Although such an effect has been predicted using the canonical equations of motion, some doubt has been raised recently as to whether it is in principle observable for a spin-1/2 particle. To resolve this issue a gedanken experiment is proposed and analyzed using wave-packet construction for the neutron beam. By allowing an arbitrary orientation for the neutron spin as well as for the electric and magnetic fields, a nonvanishing acceleration of the center of the neutron wave packet is found that confirms the predictions of the canonical formalism.

The orthonormal eigenstates of the square of Yuen’s operator b=μa+ν${\mathit{a}}^{\mathrm{°}}$ are constructed. Some mathematical and quantum statistical properties of them are discussed. A new class of minimum uncertainty state is found.

We show how the Einstein-Podolsky-Rosen paradox for continuous variables can be tested using the quadrature amplitudes of a radiation field in the pair-coherent state. Correlated pairs of photons are produced by two competing nonlinear processes—four-wave mixing and two-photon absorption.