The well-known difficulties of defining a phase operator of an oscillator are considered from the point of view of the canonical transformation to action and phase-angle variables. This transformation turns out to be nonbijective, i.e., it is not a one-to-one onto mapping. In order to make possible the unitarity of its representations in quantum optics we should enlarge the Hilbert space of the problem. In this enlarged space we find a phase operator that, after projection, reproduces previous candidates to represent a well-behaved phase operator in the quantum domain.

The system consisting of a two-level atom coupled strongly to a cavity mode behaves as a two-state system when excited near one of the ‘‘vacuum’’ Rabi resonances. With finite-bandwidth squeezed light incident upon the cavity and tuned to one of these resonances, we show that it is possible to realize a two-state system coupled to a squeezed vacuum. This system exhibits subnatural linewidths in the emitted spectra, as described by Gardiner [Phys. Rev. Lett. 56, 1917 (1986)] in a study of spontaneous emission of a two-level atom in a squeezed vacuum, but requires that only a single cavity mode be subject to squeezing rather than the entire three-dimensional vacuum.

We show that by coupling additional laser fields to a three-level atom it is possible to modify effective spontaneous emission rates and line shapes in a manner similar to that previously associated with cavities and waveguides. The effect is related to the laser-induced continuum structure discussed in the context of ionization processes.

A continuous quantum-nondemolition measurement scheme that is based on intensity dependent atomic scattering in three-state systems is analyzed. The proposed scheme measures the number of photons in an optical cavity mode by observing the scattering rate of the atomic medium. The time evolution of the coupled atom-field system is analyzed using the Monte Carlo wave-function approach. The wave-function collapse occurs continuously as a result of the presence or absence of scattering events at each time instant. It is shown that the measurement is logically reversible and the information contained in the premeasurement wave function is preserved during the measurement interaction.

The effect of a monochromatic electromagnetic field in the localization properties and tunneling rates of a two-level system is studied within a purely quantum framework. This generalizes a recent semiclassical analysis and provides analytical expressions which are valid for an arbitrary number of photons in the field. Some consequences and applications of the possibility of tunneling control in an electromagnetic cavity are discussed.

The wave-function-splitting technique which has been developed for localized potentials is generalized to long-range potentials. This technique allows for a significant reduction of the grid size without losing information. The method is demonstrated for a standard one-dimensional model and some practical details are discussed.

We describe a system of N two-level Rydberg atoms which travel through a resonant cavity and interact with a single mode of the resonator. N is assumed to be on the order of a few tens or hundreds of atoms. In particular, we analyze the case where the atoms are injected to the lower state (absorber) and the system is driven by an external coherent radiation field exactly resonant with the atoms and with the cavity. In the case of a monoenergetic atomic beam, the picture that arises is substantially different from that of standard optical bistability. The switching behavior is not governed by saturation, but by the Rabi cycles of the atoms in the cavity. The hysteresis cycle of the population of the upper level is butterfly shaped. When the bistability parameter exceeds an appropriate second threshold, the system displays multistability rather than simple bistability, and under proper conditions it develops domains of instability in positive-slope regions of the steady-state curve. We analyze the effects of a velocity distribution (thermal or Gaussian) in the atomic beam, and of inhomogeneous broadening caused by stray electric fields. Finally, we discuss the feasibility of an experimental observation of the effects predicted by our analysis.

The implications of complementarity on two-path neutron interferences and on separated-oscillatory-field resonances are discussed. The studies are extensions of those by Furry and Ramsey [Phys. Rev. 118, 623 (1960)] on two-path electron interferences which showed that an apparatus used to determine the electron path introduces uncertainties in the scalar and vector potentials which in turn disturb the phase of the electron wave function so much through the Aharonov-Bohm effects [Phys. Rev. 115, 485 (1959)] that the interference fringes disappear. A similar result is derived here for the neutron, but with the phase uncertainties coming from the magnetic moment’s motion through an electric field as discussed by Anandan [Phys. Rev. Lett. 48, 1660 (1982)], and Aharonov and Casher [Phys. Rev. Lett. 53, 319 (1984)]. A corresponding result is also obtained for separated-oscillatory-fields resonances, which can be interpreted as an interference between two different paths in spin space. An interesting difference between the separated-path and separated-oscillatory-field experiments is that the latter may be interpreted classically.

We first calculate the ‘‘exact’’ micromaser spectrum by solving numerically for the Green’s function of the approximate master equation for the one-atom (micro-) maser. We then proceed to calculate approximate analytical expressions for the maser linewidth using (i) a phase-operator approach, (ii) an ansatz similar to the standard quantum theory of the laser, and (iii) a linear expansion of the correlation function. Novel features, quite distinct from the familiar Schawlow-Townes linewidth, are found, e.g., the linewidth decreases as the number of thermal photons increases.

We calculate the micromaser spectrum via the eigenvalues and eigenvectors of the master equation. We show that (i) it is not always the lowest eigenvalue which governs the linewidth and (ii) the oscillations in the linewidth originate from an interplay between two eigenvalues.

A conceptually simple and computationally economical, ${\mathit{scrL}}^2$-discrete-basis-set stabilization method of computing a spectral density as a function of energy is presented. Photoabsorbtion to the continuum is emphasized in examples of model problems. The use of the method for computing rates and state-dependent cross sections is sketched. Traditional scattering solutions are avoided, as are dilatation analytic, imaging, and absorbing-potential techniques.

Using Weinberg’s generalized nonlinear quantum dynamics [Ann. Phys. (N.Y.) 194, 336 (1989)], we propose a simple way to form an interpolative dynamical system that joins the classical and quantum regimes. By altering a dimensionless control parameter λ∈[0,1], one can smoothly metamorphose quantum evolution into classical evolution, keeping the Hilbert-space dimension and physical constants unchanged. The method suggests an approach to studies of dynamical chaos suppression in quantized classically chaotic systems.

The dipole moment and the polarizability of the SiC molecule are calculated by using the coupled cluster with double-substitution approximation with partial inclusion of single and triple substitutions. Their respective derivatives with respect to the internuclear separation are also reported within the many-body-perturbation-theory scheme to fourth order limited to double and quadruple substitutions.

Quantum beats due to the hyperfine interaction were observed in the radiative decay of the 8${\mathit{D}}_{3/2}$ state in ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$. The data agree well with theory allowing determination of the magnetic-dipole (‖a‖=0.879±0.008 MHz) and electric-quadrupole (‖b‖=0.15±0.02 MHz) (a/b>0) hyperfine constants. The results are consistent with those obtained for other ${\mathit{D}}_{3/2}$ states in ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ and ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$. The observed magnetic-dipole constants for the ${\mathit{nD}}_{3/2}$ n>7 states of ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ are given to within 2% by the relation a(MHz)=252/${\mathit{n}}^{\mathrm{*}3}$ where ${\mathit{n}}^{\mathrm{*}}$ is the effective principal quantum number.

The distribution of isolated avoided crossings in quantum systems whose classical counterparts possess a mixed phase space of regular and chaotic dynamics is investigated. The distribution function for the width is shown to consist of two components: a near-Gaussian distribution suggested by random matrix theory for the chaotic component and an approximately δ-shaped component originating from tori in the regular portion of phase space. A statistical measure for overlapping avoided crossing based on parametric correlations of energy levels is introduced and shown to be sensitive to the fraction of classically chaotic phase space.

The electron-pair density I(u) of an atomic system, u being the interelectronic vector ${\mathbf{r}}_{12}$, may be completely characterized by means of the moments 〈${\mathit{u}}^{\mathit{q}}$〉, q>-3, defined as 〈${\mathit{u}}^{\mathit{q}}$〉=F${\mathit{u}}^{\mathit{q}}$I(u)u =4π${\mathcal{F}}_0^{\mathrm{\infty }}$${\mathit{u}}^{\mathit{q}+2\mathrm{}}$h(u)du, where h(u) is the spherical average of I(u). These interelectronic quantities are basic elements in the study of the electron-electron correlation problem. Here it is analytically shown how a moment of a given order q is bounded from below in terms of moments with orders higher than or lower than q. To do that, the so-called extended-correlation cusp condition [i.e., h(u)-h’(u)≥0 for u≥0], recently found for various atomic systems in a variational Hylleraas-type framework, is used. The lower bounds turn out to be often very accurate.

It is shown how the results of a recent experiment by Jiang, Zuo, Vušković, and Bederson [Phys. Rev. Lett. 68, 915 (1992)], who investigated low-energy electron scattering from laser-excited polarized sodium atoms in the initial (3p) ${}_{}{}^2{}_{}{}^{}$P${\mathrm{°}}_{3/2}$ (F=3, ${\mathit{M}}_{\mathit{F}}$=3) state, can be related to the inelastic 3S→3P transition involving initially unpolarized electron and atom beams. Hence, this method can provide an independent check of the traditional electron-scattering experiment with unpolarized beams.

We report a measurement of the energy dependence of the branching ratios for autoionization of the (6${\mathit{p}}_{1/2}$ns${)}_{\mathit{J}=\mathit{M}\mathit{J}}$=1 state of barium into the 6${\mathit{p}}_{1/2}$εl continuum channels by monitoring the polarized residual ion fluorescence signals. This measurement shows good agreement with a recent R-matrix calculation.

We present a detailed theoretical study of the very narrow A=- and A=0 series seen in the recently reported high-resolution photoionization spectrum of He below the N=2 threshold [M. Domke et al., Phys. Rev. Lett. 66, 1306 (1992)]. The hyperspherical close-coupling method combined with the multichannel quantum-defect theory is used and the photoionization cross section has been calculated over a wide energy range with high efficiency. Our results are in excellent agreement with the experimental data and compare favorably with recent accurate theoretical works.

We report an experimental observation of coherent population transfer in a multilevel system by adiabatic following through a trapped state. Raman transitions between ground-state sublevels are induced by two partially overlapping ${\mathrm{\sigma }}^{\pm }$ polarized laser beams, tuned to the hyperfine transition F=4→F’=4 of the cesium ${\mathit{D}}_2$ line. An efficiency of more than 50% is observed for the ${\mathit{m}}_{\mathit{F}}$=+4→${\mathit{m}}_{\mathit{F}}$=-4 population transfer. The influence of other excited hyperfine levels on the transfer efficiency is pointed out. The feasibility of the technique with counterpropagating laser beams is also demonstrated.