Utilizing a classical model, the interaction of a centrally positioned radiating dipole with a finite-sized spherical Bragg structure is treated. A straightforward approach is adopted to calculate the radiative lifetime and resonance frequency shifts of a source within a three-dimensional Bragg structure, and applied to a simple physical system that can be expected to provide a good estimate of the finite-size effects that will occur in more complicated structures. These calculations are of fundamental theoretical interest for understanding dipole-surface interactions, particularly in spherical geometries requiring a vector formulation. The work is of potential practical interest as applied to spherical cavity and photonic structure design, and stresses the connection between recent photonic band-gap research and the earlier investigations of dipole-mirror interactions.

Low-frequency fluctuations observed in the coherence collapse of semiconductor lasers are numerically investigated based on the Lang-Kobayashi model. It is found that the attractor in the compound cavity mode loses its stability due to a crisis with an antimode. Chaotic itinerancy among the destabilized compound cavity modes is also found.

A quantum phase description is developed by the use of the antinormal ordering of Susskind-Glogower phase operators. The theory is studied in the infinite-dimensional Hilbert space and it is closely related to the Pegg-Barnett quantum phase description in the finite-dimensional Hilbert space with a proper limiting procedure. Various applications of the antinormal ordering technique are presented.

Recently we have observed the Stark shift in an optical transition of a single trapped ${\mathrm{Ba}}^{+}$ ion. To enhance the shift in the 6${\mathit{S}}_{1/2\mathrm{-}}$5${\mathit{D}}_{5/2}$ clock transition, the ion is displaced from the saddle point of the trapping potential. The Stark shift constants, ${\mathrm{\sigma }}_{\mathit{s}}$, for the three pairs of Zeeman components are found to be the following: 6.1(7), 7.5(8), and 11.7(12) mHz/(V/cm${)}^2$ for ‖${\mathit{M}}_{\mathit{S}}$‖=1/2 to ‖${\mathit{M}}_{\mathit{D}}$‖=1/2, 3/2, and 5/2 transitions, respectively. A scheme is also proposed to use the Stark shift to identify the zero-point confinement state of a single trapped ${\mathrm{Ba}}^{+}$ ion.

The effect of decoherence is analyzed for a free particle interacting with an environment via dissipative coupling. The interaction between the particle and the environment occurs by a coupling of the position operator of the particle with the environmental degrees of freedom. By examining the exact solution of the density-matrix equation, one finds that the density matrix becomes completely diagonal in momentum with time, while the position space density matrix remains nonlocal. This establishes the momentum basis as the emergent ‘‘preferred basis’’ selected by the environment, which is contrary to the general expectation that position should emerge as the preferred basis, since the coupling with the environment is via the position coordinate.

A class of positive quantum phase-space distributions based on antinormal ordering of the squeezed-photon annihilation and creation operators is introduced. This class of distributions, referred to as the generalized antinormally ordered distributions, is shown to be generated when the Wigner distribution is smoothed with a squeezed Gaussian wave packet. The distribution function associated with generalized antinormal ordering can thus be identified as the Husimi distribution function. The usefulness of the distributions in studies of the quantum particle dynamics is illustrated with simple examples.

We measured the photoabsorption spectrum of sodium in the 2p subshell excitation region using synchrotron radiation and a 3-m spectrograph at a resolution of ±0.008 Å. In spite of the large number of overlapping structure due to the four ionization limits 2${\mathit{p}}^5$3s${(}^3$${\mathit{P}}_{210}$ and ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}_1$), well separated autoionizing Rydberg series are detected converging to the 2${\mathit{p}}^5$3s${(}^1$${\mathit{P}}_1$) threshold. A three-channel quantum-defect-theory analysis is performed for the 2${\mathit{p}}^5$3s${(}^1$${\mathit{P}}_1$)ns and 2${\mathit{p}}^5$3s${(}^1$${\mathit{P}}_1$)nd autoionizing resonances. A simple n-channel multichannel quantum-defect-theory formula in terms of cofactors is presented for the calculation of the photoionization cross section for one open and (n-1) bound channels.

The weak capture of negative muons on protons has been calculated in the local V-A theory in the correct spinor representation for μp atoms and pμp molecules. The neutrino-mass effects have been explored. The results obtained by this formal theory are compared with earlier calculations, and their importance is discussed in the light of the experiments.

Laser excitation of a fast beam of ${\mathrm{Yb}}^{+}$ ions has been used to make measurements of the radiative lifetimes of eight Yb ii energy levels, four of which were excited via transitions from the ion-trap metastable level 4${\mathit{f}}^{13}$6${\mathit{s}}^2$ ${}_{}{}^2{}_{}{}^{}$${\mathit{F}}_{7/2}^{\mathit{o}}$. Comparison is made with the lifetimes that may be derived from the semiempirical pseudorelativistic Hartree-Fock calculation by Fawcett and Wilson [At. Data Nucl. Data Tables 48, 241 (1991)], the agreement being within 50% for seven of the eight levels considered.

It has recently been shown that a harmonic perturbation of a potential barrier increases the tunneling if the energy of the incident particle is significantly below the barrier height. We show that this result holds even if a noise is introduced into the perturbation of the potential barrier.

For the purposes of computing resonance parameters an alternative version of the stabilization method is used in a simpler way than previously reported [V. A. Mandelshtam, T. R. Ravuri, and H. S. Taylor, Phys. Rev. Lett. 70, 1932 (1993)]. The method is based on the calculation of the eigenphase sum, which, as is shown, can be extracted easily from a stabilization diagram.

The eigenstates are constructed for a Paul-trapped particle in an intense laser field. This is done by using a time-dependent unitary transformation. The application of these results is discussed.

We study Floquet eigenstates of an atom exposed to a laser field with an electric-field amplitude beyond the typical inner atomic field. We focus on the frequency dependence of these eigenstates for a fixed oscillation amplitude. The results are in agreement with previous analytical calculations for high frequencies but differ considerably for the moderate frequencies usually used in time-dependent studies. The Floquet states for moderate frequencies are not time independent, cannot be chosen to be real, and do not show the dichotomy known from the high-frequency Floquet states. The importance of the Floquet state for the interpretation of solutions of the time-dependent Schrödinger equation is demonstrated.

The interaction of a quantized field mode with N identical atoms coupled to individual reserviors and classical driving fields is studied. An effective time-evolution operator for the radiation mode is derived. The exponent of this operator can be written as the number of atoms times an infinite sum containing field operators and correlation functions of freely evolving (no atom-field coupling) single-atom operators. In the adiabatic limit of fast decaying atomic correlations one can derive a master equation for the field density matrix. It is shown that the Liouvillian describing the interaction of the field mode with the N atoms is N times the single-atom Liouvillian.

We discuss how transparency and population trapping effects are affected when a realistic continuum is involved. We consider the propagation of matched pulses in a Λ-like system, where the upper level is replaced by a continuum.

We have constructed the multimode bosonic realization of the su(2) Lie algebra, on the basis of which the SU(2) generalized coherent state in the multimode Fock space is derived. It is shown that in the multimode coherent state each bosonic mode has the sub-Poissonian statistics, and that the unitary displacement operator can be identified as the generalized multimode rotation operator.

Unitary equivalence between the ideal and feasible phases is proven. The ideal phase can be described by the phase operator D${\mathrm{^}}_{\mathrm{RNS}}$, constructed from the relative-number states, and the feasible phase considered here is characterized by the Shapiro-Wagner phase operator D${\mathrm{^}}_{\mathrm{SW}}$. The unitary operator W^ satisfying D${\mathrm{^}}_{\mathit{S}\mathit{W}}$=W^D${\mathrm{^}}_{\mathrm{RNS}}$W^ ${}_{}{}^{\mathrm{°}}{}_{}{}^{}$ and D${\mathrm{^}}_{\mathrm{RNS}}$=W^ ${}_{}{}^{\mathrm{°}}{}_{}{}^{}$D${\mathrm{^}}_{\mathrm{SW}}$W^ is derived. :

An experiment that would measure noncommuting quantum-mechanical observables without collapsing the wave function has been recently proposed by Y. Aharonov, J. Anandan, and L. Vaidman [Phys. Rev. A 47, 4616 (1993)]. These authors argue that this ‘‘protected measurement’’ may give an indication on ‘‘the reality of the wave function.’’ We show that the proposed experiment admits a much simpler interpretation: it is an experiment in which the quantum system is (assumed to be) in an eigenstate of the observable being measured. As such, the fact that no collapse occurs is trivial and can be understood without the need of the concept of ‘‘protective’’ devices. We argue that the experiment does not provide a way for measuring noncommuting observables without a collapse, does not bear on the issue of the ‘‘reality of the wave function,’’ and does not add any particular insight into our understanding (or nonunderstanding) of quantum mechanics.

Recent experimental measurements of charge transfer in ion collisions with circular-state Rydberg atoms (for which m=l=n-1) can be qualitatively reproduced using an elementary atomic model consisting of a classical electron in a circular orbit with an arbitrary axis of rotation defined by experiment. Contributions to capture are further separated into one-swap and three-swap charge transfers, revealing the relative importance of a Thomaslike mechanism for charge transfer at ion velocities of 1.00, 1.65, and 2.00 times the velocity of the target electron. The model is extended to estimate charge-transfer cross sections for ions incident on elliptic-state Rydberg atoms of specific eccentricity.