A random-matrix theory is presented for the linewidth of a laser cavity in which the radiation is scattered chaotically. The linewidth is enhanced above the Schawlow-Townes value by the Petermann factor K, due to the nonorthogonality of the cavity modes. The factor K is expressed in terms of a non-Hermitian random matrix, and its distribution is calculated exactly for the case in which the cavity is coupled to the outside via a small opening. The average of K is found to depend nonanalytically on the area of the opening, and to greatly exceed the most probable value.

Photoabsorption of neon in the region of the inner shell excited ${1s}^{-1}\mathrm{np}$ resonance series is treated using an optical potential R-matrix method. Compared to standard R-matrix results, an extremely broadened resonance profile is determined, due to implicit inclusion of core Auger decay states via the optical potential, remarkably reproducing recent high-precision experimental results.

The polarizabilities of Si clusters with 9 to 28 atoms are calculated using a density functional cluster method. The atomic geometries are based on those carefully optimized by energy minimization. The polarizability shows fairly irregular variation with cluster size, but all calculated values are higher than the polarizability of a dielectric sphere with bulk dielectric constant and equivalent volume.

Drift of optically active atoms in a buffer gas induced by an incident light field is a consequence of the unequal diffusive frictions suffered by the excited and the ground-state atoms. We investigate this light-induced drift in the presence of a magnetic field in a direction perpendicular to the incident light, which gives rise to an interesting effect, appropriately called the “optical Hall effect.”

The connection between wave functions of harmonic plus inverse harmonic potential with time-dependent mass and frequency and those of harmonic plus inverse harmonic potential with time-dependent frequency is investigated. Thus the correct wave function of the harmonic plus inverse harmonic potential with time-dependent mass and frequency is obtained.

In reply to the Comment by Maamache on Phys. Rev. A 58, 1574 (1998), it is shown first that the $\mathrm{M¨}\mathrm{}\left(t\right)\mathrm{}$ terms are canceled and then that the wave function [Eq. (34)] is an eigenfunction of the invariant of Eq. (19).

By expanding optical response functions in the eigenstates of the dipole operator (rather than of the Hamiltonian), we obtain a path-integral representation that lends itself more readily to classical simulations. Connection is made to stochastic (consistent-histories) theories of quantum dynamics of single quantum systems by computing the entire probability distribution of the observed polarization (rather than merely its expectation value). The weight of each Liouville space path contributing to the optical response is complex, and cannot be recast using the joint probabilities used in the consistent-histories approach.

Spontaneous parametric down-conversion is a convenient source of pairs of entangled photons. Within special interferometric configurations involving either two sources of this kind or double emissions from such a source, one can observe three-photon Greenberger-Horne-Zeilenger–type interference effects. Unfortunately, events of some other types necessarily occur. It is shown that under specific operational conditions, thus far not met by the experiments, the entirety of the phenomena observed in such experiments has no local realistic model. However, one can show this only by analyzing the entire pattern of all events predicted by quantum mechanics.

One of the cornerstones of many areas of physics (such as quantum optics, laser theory, and cavity QED) is the rotating-wave approximation (RWA) to the Hamiltonian for a dipole-oscillator coupled to the radiation field. Here it is shown that within the RWA one can obtain explicitly an exact expression for the autocorrelation of the force exerted by the field on the oscillator. This exact result differs from that appearing in much of the standard literature in that the spectrum is not that of white noise and there is no nontrivial dependence on the oscillator frequency.

We show that squeezed vacuum state and Fock states can be used to test Bell’s inequalities by means of two-mode Wigner function measurement. High quantum efficiency optical homodyne tomography and cascaded optical homodyning ensure these proposals to be practical experimentally.

A quantum computer based on an asymmetric coupled-dot system has been proposed and shown to operate as a controlled-NOT gate. The basic ideas are the following. (1) The electron is localized in one of the asymmetric coupled dots. (2) The electron transfer takes place from one dot to the other when the energy levels of the coupled dots are set to be close. (3) The Coulomb interaction between the coupled dots mutually affects the energy levels of the other coupled dots. The decoherence time of the quantum computation and the measurement time are estimated. The proposed system can be realized by developing the technology of the single-electron memory using Si nanocrystals, and a direct combination of the quantum circuit and the conventional circuit is possible.

The ytterbium ion has a rich level structure of low-lying states, and is one of the most widely used in experiments with trapped ions. We have measured the radiative lifetimes for the two ${4f}^{14}5d$ metastable states using single ytterbium ions confined in a rf trap. The obtained lifetimes for $D_{3/2}$ and $D_{5/2}$ states are 52.7(2.4) and 7.0(0.4) ms, respectively. The results are in good agreement with previously measured values, but differ significantly from theoretical estimates. The $P_{1/2}$ branching ratio into $D_{3/2}$ has also been obtained from the experiment to be 0.0483 with a 9% uncertainty.

Low-energy muon-transfer cross sections and rates in collisions of muonic atoms with hydrogen isotopes are calculated using a six-state close-coupling approximation to coordinate-space Faddeev-Hahn-type equations. In the muonic case satisfactory results are obtained for all hydrogen isotopes and the experimentaly observed strong isotopic dependence of transfer rates is also reproduced. A comparison with results of other theoretical and available experimental works is presented. The present model also leads to good transfer cross sections in the well-understood problem of antihydrogen formation in antiproton-positronium collision.

We present measurements of projectile angular differential cross sections, $d\sigma /d\theta ,$ and mean projectile energy gain or loss, $\Delta E_{\mathrm{mean}},$ as functions of the number s of electrons stabilized on the projectile in 16- and 26.4-keV ${\mathrm{Ar}}^{8+}+{\mathrm{C}}_{60}\to {\mathrm{Ar}}^{\left(8\mathrm{}-s\right)+}+{\mathrm{C}}_{60}^{r+}+(r-{s)e}^{-}$ collisions. These results are discussed in view of two models of the electronic response of ${\mathrm{C}}_{60}.$ In the infinitely conducting sphere model the charge mobility is sufficiently high in order to average out all effects of localization of individual charge carriers. In the movable-hole model “positive holes” are assumed to be localized as point charges in their equilibrium positions on the “molecular surface” within the times (down to ${10}^{-16}\hspace{0.5em}\mathrm{s})$ between sequential over-the-barrier electron transfers. The two sets of predictions for $\theta$ are close for $r<~8,$ and for $r<~5$ they are also in agreement with experimental results indicating ultrafast electronic response of ionized ${\mathrm{C}}_{60}.$ For $r>\mathrm{}5,$ both models underestimate $\theta$ and therefore we have developed Monte Carlo calculations for close collisions with individual carbon atoms in ${\mathrm{C}}_{60}.$ The energy gain first increases with s, has a flat maximum around $s=4\mathrm{}$ and yields mean energy loss $\Delta E_{\mathrm{mean}}=-20\pm 5\hspace{0.5em}\mathrm{eV}$ for $s=7.\mathrm{}$ The measured fragmentation spectra $\theta \mathrm{}\left(s\right)\mathrm{}$ and $\Delta E_{\mathrm{mean}}\mathrm{}\left(s\right)\mathrm{}$ may be partially rationalized by combining each of the two smooth-sphere models with the Monte Carlo calculations for close collisions.

A high-resolution $4d$ photoelectron spectrum of Eu has been measured. The spectrum reveals a rich structure reflecting multiplet splitting due to $4d-4f,$ $4f-4f,$ and spin-orbit interaction. In order to interpret the complex ${4d}^{-1}$ multiplet structure, calculations in the intermediate coupling scheme were performed taking into account the term-dependent lifetime width of each ${4d}^{-1}$ multiplet state. The strong influence of both the $4d-4f$ exchange interaction and the term-dependent lifetime broadening on the shape of the $4d$ photoelectron spectrum is demonstrated. Due to the inner-shell character of the $4d$ and $4f$ orbitals, the spectrum of atomic Eu is similar to that of Eu and Gd solid samples having the same ${4f}^7$ occupancy.

Absolute doubly differential electron-loss cross sections were measured for ${\mathrm{H}}^0,$ ${\mathrm{H}}_2^{+},$ ${\mathrm{D}}^0,$ ${\mathrm{D}}_2^{+},$ ${\mathrm{He}}^0,$ and ${\mathrm{He}}^{+}$ on neon at 0.1 and 0.5 MeV/amu in order to investigate the velocity dependence and any projectile dependence of the electron spectra. An additional measurement of target ionization in 0.1 MeV/amu ${\mathrm{Ne}}^0+\mathrm{H}\mathrm{e}$ collisions in comparison with electron loss from 0.1 MeV/amu ${\mathrm{He}}^0+\mathrm{N}\mathrm{e}$ was aimed at testing the method of “inverse kinematics” for a collision system where the electron angular distribution is dominated by a distinct Ramsauer-Townsend minimum. The measured absolute singly differential cross sections, transformed to the neon frame of reference, agree well over the whole angular range (0°–180°), thereby establishing this as a useful method when high-energy beams of a particular projectile are not readily available. Calculations using both the on-shell and off-shell version of the electron impact approximation show that the quasielastic scattering theory is rather poor at such low collision velocities, but nevertheless reveal the importance of doubly inelastic processes in the case of both ${\mathrm{He}}^0$ and ${\mathrm{He}}^{+}$ ionization. Satisfactory agreement between theory and experiment was obtained at the higher velocity. The ${\mathrm{H}}_2^{+}$ and ${\mathrm{D}}_2^{+}$ results show evidence of molecular effects.

The spontaneous decay rate $\gamma$ of excited atomic states limits the radiative force on atoms to $ħk\gamma /2.\mathrm{}$ This bottleneck in the dissipative exchange of momentum between atoms and light can be overcome by coherent control of the momentum exchange interactions. The bichromatic force provides such control by using stimulated instead of spontaneous emission to produce the force, while at the same time exploiting spontaneous emission to enable a dissipative interaction. It is implemented with two counterpropagating light beams, each containing two frequencies, whose phases, amplitudes, and frequency difference are carefully chosen. We have made precise measurements of the extremely large magnitude and velocity range of this bichromatic force, and have shown that its velocity dependence near the edge of its range is suitable for atomic beam slowing and laser cooling. Our measurements have corroborated various models and calculations of this bichromatic force.

A two-level atom coupled to a reservoir with Lorentzian spectral response function is considered. It is shown that if the free oscillations of the atomic dipole are suitably modulated by an external field, then the dynamics of the spontaneous decay can be strongly modified. As a result, the probability of finding the atom in an excited state can be large even for very long times. This is because the frequency modulation may lead to both effective detuning of the atom from the resonance with reservoir modes and to effective cancellation of the coupling between the atom and the reservoir. Non-Markovian features of the reservoir are found to be essential for this effect to be observable. Conditions of experimental verifications are provided.

The isotope shifts for $2{}^2{P}_J$–$2{}^{2}S$ and $3{}^{2}S$–$2{}^{2}S$ transition energies in lithium are calculated variationally in Hylleraas coordinates, including nonrelativistic, relativistic, and QED terms up to $O(\mu /M),$ $O(\mu {/M)}^2,$ $O({\alpha }^2\mu /M),$ and $O({\alpha }^3\mu /M)$ atomic units, and the lowest-order finite nuclear size correction. With high-precision isotope shift measurements, our results can potentially yield a precise determination of the nuclear charge radius for different isotopes of lithium, and especially for the exotic ${}^{11}$Li “halo” isotope. For the case of ${}^7\mathrm{Li}$-${}^6\mathrm{Li},$ using the nuclear charge radii from nuclear scattering data, our calculated isotope shifts for the $2{}^2{P}_{1/2}$–$2{}^{2}S,$ $2{}^2{P}_{3/2}$–$2{}^{2}S,$ and $3{}^{2}S$–$2{}^{2}S$ transitions are $10534.31\left(61\right)\mathrm{}\left(6\right)\mathrm{}$ MHz, $10534.70\left(61\right)\mathrm{}\left(6\right)\mathrm{}$ MHz, and $11454.31\left(39\right)\mathrm{}\left(5\right)\mathrm{}$ MHz, respectively, where the first brackets indicate the uncertainties due to the nuclear charge radii, and the second brackets indicate the computational uncertainties. The experimental isotope shifts are inconsistent with each other and with theory for these transitions.