The experimental data obtained by Hoogeveen et al. [Phys. Rev. A 39, 5539 (1989)] on light-induced viscous flow in a gas are theoretically explained for the entire range of pressure used. The observed data can be successfully accounted for by means of generalized hydrodynamic equations for radiation and matter. In particular, the low-pressure data are closely related to the Knudsen problem observed in the tube flow of rarefied gases.

The paper deals with the micromaser theory in which the cavity-reservoir coupling is considered during the atom-field interaction. The evolution of the cavity radiation when it contains no atom is included as usual. This brings out the dependence of the photon statistics on the cavity leakage. The possibilities of generating a Fock state of the radiation field are analyzed.

The Wigner and Glauber-Sudarshan P functions for quantum fields are usually defined in terms of integrals over the phase space of characteristic functions. We show that they and, in general, any s-parametrized quasiprobability distribution may be represented as a series in terms of displaced number states facilitating a straightforward evaluation.

We study the chaotic behavior of the internal field in a micromaser with injected atomic coherence. The quantum dynamics provides a return map in the semiclassical limit which we study as a function of the reduced atom-field interaction time. Bifurcations, chaos, and transitions between bifurcation sequences appear in a broad range of the parameter space.

We investigate spontaneous emission into an electromagnetically produced transparency of the form recently proposed [A. Imamoǧlu and S. E. Harris, Opt. Lett. 14, 1344 (1989)]. We show that the achievable radiation temperature (or brightness) at the transparency is much greater than the atomic temperature.

Harmonic spectra have been calculated by numerically integrating the one-dimensional Schrödinger equation for a model potential and a laser field sufficiently intense to cause significant or complete ionization. The use of a one-dimensional model allows realistic pulse lengths (1 ps) and laser wavelengths (0.5 and 1 μm) to be considered. The dependence of the plateau cutoff on laser intensity has been studied in detail, from far below to far above the saturation intensity. We find that below saturation the cutoff scales approximately linearly with laser intensity, and that the cutoff continues to increase beyond saturation, although at a slower rate. At high intensities, where ionization occurs rapidly during the leading edge of the laser pulse, the edge of the plateau becomes less clearly defined. In this regime, the harmonic cutoff will be determined by a combination of the atomic response and the phase mismatch due to the presence of free electrons.

A quantum optical model with a classical phase space exhibiting nonlinear oscillations around two elliptic fixed points is investigated. The quantum system is found to display coherent tunneling between near coherent states of opposite phase centered at the classical fixed points.

Namiki and Pascazio [Phys. Rev. A 44, 39 (1991)] propose a model of wave-function collapse associated with the nonfiring of a detector in one of two paths for which a particle is known to be present, and argue that the collapse has the same status as the collapse associated with a measurement involving an actual detection. I question this proposal on the following grounds: (i) it is based on a shift in detection probabilities in the two paths while there is no shift in wave-function amplitudes, and (ii) Namiki and Pascazio use an insufficient measure, loss of interference, as an indicator of collapse.

We discuss and clarify the concept of dephasing in the many-Hilbert-space approach to the quantum measurement problem. We argue that the phase randomization provoked by a detecting macroscopic device is responsible for the loss of quantum coherence, and that the ‘‘collapse of the wave function’’ is to be regarded as a statistical process for the accumulated distribution over many events. In stressing the fundamental differences between our approach and the Copenhagen interpretation, we counter the objections put forward by Johnston [preceding Comment, Phys. Rev. A 48, 2497 (1993)], whose standpoint is essentially similar to the Copenhagen one.

We examine results presented by Fearn and Lamb [Phys. Rev. A 46, 1199 (1992)], who search for, but fail to find, the quantum Zeno effect in measurements of the position of a particle in a double potential well, and criticize the basic statement of the effect given by Misra and Sudarshan [J. Math. Phys. 18, 756 (1977)]. We suggest that position measurements are an inappropriate area to look for the effect; nevertheless, we show that some of the results of Fearn and Lamb should, and do, exhibit a form of weak effect. Though the collapse postulate, as used by Misra and Sudarshan, is not required to discuss quantum measurement and the quantum Zeno effect, its application describes adequately the results of measurement, and we reject the idea that the basic statement of the quantum Zeno effect is flawed.

This is a Reply to the preceding Comment by Home and Whitaker [Phys. Rev. A 48, 2502 (1993)]. Our aim is to indicate how we apply basic quantum mechanics to quantum measurement theory. We discuss the work of Misra and Sudarshan [J. Math. Phys. 18, 576 (1977)] and defend our own work on the quantum Zeno effect.

Explicit examples are presented to illustrate the presence of a more symmetric resonant structure in spectra from bound excited states of a divalent atom. Comparison between the theoretical ground-state and bound excited-state photoelectron spectra shows that both the resonant energy ${\mathit{E}}_{\mathit{r}}$ and the resonant width Γ of a doubly excited autoionization state of a divalent atom (e.g., alkaline-earth-metal atom) can be determined experimentally from photoionization originated from a bound excited state more effectively.

We examine spinor evolutions in a general time-dependent magnetic field B. We derive a condition the B variation must satisfy in order that the effective field direction ${\mathbf{r}\mathbf{⁁}}_{\mathrm{B}}^{\prime }$ for a frame rotating with B becomes stationary in that frame. This condition is both sufficient and necessary for B to bring about a spinor evolution which exactly maintains a fixed angle between the spin and B. The adiabatic evolution used by Berry is just a special case, albeit only approximate, of these fixed-angle evolutions. To the other extreme of the fixed-angle evolutions, the nontrivial parallel transportation occurs, which is exact, necessarily nonadiabatic, and yields a pure geometric phase. Hence an experiment aimed at observing the geometric phase should seek to effect not an adiabatic evolution but a parallel transportation.

The ratio of double-to-single ionization of He has been measured between 280 and 1210 eV to investigate its behavior in this partially unexplored region. These measurements, compared with the most recent theories of Pan and Kelly (private communication) and of Hino [Phys. Rev. A 47, 4845 (1993)], show the importance of including not only ground-state but also final-state correlations, in contrast to the high-energy behavior discussed by Dalgarno and Sadeghpour [Phys. Rev. A 46, R3591 (1992)] where consideration of final-state correlations proves inessential. Our intermediate-energy results also appear to indicate the importance of including higher-order effects in the theory.

A strong angular dependence has been found first in the neutral fraction of medium-energy hydrogen emerging from ${\mathrm{NiSi}}_2$(111). The angular dependence can be explained well in terms of the atomic arrangement and composition of the ${\mathrm{NiSi}}_2$(111) surface and impact-parameter- (trajectory) dependent charge-exchange processes at a few atomic layers beneath the exit surface.

Quantum interference effects occurring in photodetachment of ${\mathrm{H}}^{\mathrm{-}}$ in the presence of a uniform, static electric field are shown theoretically to be controllable through use of short laser pulses having characteristic times comparable to photodetached electron reflection times. In particular, calculated cross sections for single-photon detachment by two laser pulses that are delayed and phase shifted relative to one another are shown to oscillate as a function of the relative phases of the laser pulses at fixed photodetached electron energy.

The contribution of excited metastable He projectiles to the production of the forward electron cusp peak has been measured for bombardment of Ar by 400-keV neutral He atoms using the technique of collisional quenching to control the metastable fraction of the beam. The cross section for the production of cusp electrons via target ionization by metastable He atoms has been found to be about 10 times larger than the cross section for the same process for ground-state projectiles.