In this paper we investigate the properties of a four-level atomic system interacting with two modes of the electromagnetic field in a cavity. By linearization of the Hamiltonian we show that the corresponding mathematical model is exactly solvable. To obtain simpler effective Hamiltonians the method of multiple scales is applied. It is shown that under some special values of the detunings and coupling constants, exactly predictable collapses and revivals in the atomic populations appear. Also, due to the specific interactions of the atom with the cavity modes and the ensuing measurement of energy or angular momentum and energy, two-mode Schrödinger-cat states arise in the cavity. Finally, the stabilization and trapping properties of the system are demonstrated in a lossy cavity within the Wigner-Weisskopf approximation. The existence of stationary states is shown and it is also shown that interference effects can cause cancellation of one line in both transmitted light and spontaneous emission spectra.

Coarse-grained phase distributions are introduced that approximate to the Susskind-Glogower cosine and sine phase distributions to any desired degree of accuracy. The integral relations between the phase distributions and the phase-parametrized field-strength distributions observable in balanced homodyning are derived and the integral kernels are analyzed. It is shown that the phase distributions can be directly sampled from the field-strength distributions which offers the possibility of measuring the Susskind-Glogower cosine and sine phase distributions with sufficiently high precision. Numerical simulations are performed to demonstrate the applicability of the method.

We study degenerate three-photon down-conversion as a potential scheme for generating nonclassical states of light that exhibit clear signatures of phase-space interference. The Wigner function representing these states contains an interference pattern manifesting quantum coherence between distinct phase-space components and has substantial areas of negativity. We develop an analytical description of the interference pattern, which demonstrates how the oscillations of the Wigner function are built up by the superposition principle. We analyze the impact of dissipation and pump fluctuations on the visibility of the interference pattern; the results suggest that some signatures of quantum coherence can be observed in the presence of a moderate amount of noise.

The dynamics of a unidirectional erbium-doped fiber laser is investigated on a time scale short enough to observe, with good resolution, its behavior for individual round-trips in the laser cavity. With an intracavity polarization controller, a rich variety of nonlinear phenomena, ranging from self-pulsing to square-wave antiphase patterns in two orthogonal states of polarization, are observed. These patterns evolve continuously in time. A stochastic delay-differential equation model is proposed to describe this system. Numerical simulations show that this model satisfactorily accounts for all types of qualitative behavior and reveal that the inclusion of spontaneous-emission noise is necessary to reproduce the observed continuous pattern evolution. Two different, typical types of nonlinear dynamical states are found both numerically and experimentally: a deterministic, low-dimensional regime and a noise-driven high-dimensional motion.

We consider a dispersive effective coupling between the internal energy electronic levels of an ion in a trap with its own center-of-mass motion. By using a procedure similar to the Ramsey oscillatory method, a quantum nondemolition experiment of the center-of-mass vibration population number is proposed. A procedure to generate squeezed states and Schrödinger-cat-like states that are superpositions of squeezed states is also suggested.

It is shown that two identical systems, not interacting with each other but resonantly coupled with the same intense radiation field, can be correlated. The case of a pair of two-level atoms is quantitatively investigated by calculating the probability for the emission of a photon by one of the two atoms. One finds that the presence of the other atom strongly affects the shape of the resonance curve. It is concluded that this effect, called signal transmission by means of optical correlations, if observable, could be the way for transmitting information between the atoms without resorting to any modulation of the field amplitude.

The penetration depth and pseudomomentum (wave vector) of evanescent electromagnetic waves are measured at a planar dielectric surface by means of laser spectroscopy using the Cs ${\mathrm{D}}_2$ line with a wavelength of 852.1 nm. The same experimental setup is employed in all the experiments. The first result shows a sharp, asymmetric absorption profile, which is explained in terms of the thin penetration depth, and the second shows an actual transfer of the pseudomomentum of the surface electromagnetic mode to atoms via a resonance interaction. The measured penetration depth and pseudomomentum agree with the natural interpretation of the complex wave number characterizing evanescent waves at a planar dielectric-vapor interface. Direct excitation of evanescent waves by excited Cs atoms has also been observed as atomic fluorescence emitted into the dielectric material at the angle of total internal reflection. The results are in good agreement with the theoretical predictions and exhibit the characteristics of excitation transfer or tunneling from Cs atoms into the surface mode.

We study squeezing in electromagnetic field quadrature components, produced by a collection of A two-level atoms interacting with a single mode of a strong electromagnetic field. We present analytic results both for short and long interaction times. At short times, squeezing grows with the number of atoms for a given initial number of photons. The maximum squeezing which can be achieved in a strong-field case is 66%. At long interaction times, collective effects increase the quadrature fluctuations, compared to the single-atom case. However, for a given number of atoms A, any initial pure atomic state exhibits squeezing when the mean photon number of the initial coherent field satisfies the condition n-bar>(2A${)}^4$ . At times close to the first revival, strong squeezing can be achieved for special initial atomic conditions.

We have investigated the influence of intrinsic laser noise on recently proposed schemes for targeting laser dynamics to unstable periodic orbits by means of Q switching of modulated class-B lasers. Several interesting features of turn-on statistics in such a nonlinear regime have been found, including scaling of targeting peaks location with the strength of the spontaneous emission noise and universality of the transient time statistics, i.e., their essential independence of the strength of noise. The concept of the highest passage times has been introduced and their distribution functions double-peaked structure with the underlying symmetry properties has been revealed and explained. The noise has been found to cause much more frequent phase switching in comparison with the deterministic case with possible detrimental effects on the use of this particular scheme in chaos control techniques.

The basic properties of the ground states in the four-body muon molecules ppμμ, pdμμ, ptμμ, ddμμ, dtμμ, and ttμμ are calculated. It is found that the nuclear reaction rates (${\mathrm{R}}_{\mathrm{f}}$) in such four-body molecules are significantly larger than for the corresponding three-body ions with the same nuclei: ppμ, pdμ, ptμ, ddμ, dtμ, and ttμ. In particular, for the dtμμ system ${\mathrm{R}}_{\mathrm{f}}$(dt)≈3×${10}^{13}$–6×${10}^{13}$ ${\sec }^{\mathrm{-}1}$, which is ≈40 times greater than the respective ${\mathrm{R}}_{\mathrm{dt}}$(dtμ) value.

We compare the recent pseudopotential calculation of potential curves for ${\mathrm{K}}_2$ and NaK molecules [Phys. Rev. A 54, 204 (1996)] with the newest experimental data on selected molecular states. It is shown that our experimental results reduce the discrepancies between theory and experiment.

In the hyperspherical coordinates, by using splines as basis functions we can accurately calculate the energy levels of helium. Unlike the standard configuration-interaction (CI) method and the modified configuration-interaction (MCI) method [S. P. Goldman, Phys. Rev. Lett. 73, 2541 (1994)], which involve two-dimensional integrations, our method involves only one-dimensional integrations. Also, given the excellent numerical properties of B splines, we are able to obtain the ground-state energy of helium, using only double precision calculations, with relative errors of 3.8×${10}^{\mathrm{-}8}$, which is almost 3 orders of magnitude better than the usual CI method.

Atomic many-body theory methods are used to calculate the fine structure of negative ions formed by binding a p electron into an open shell, ${\mathrm{Ca}}^{\mathrm{-}}$, ${\mathrm{Sr}}^{\mathrm{-}}$, ${\mathrm{Ba}}^{\mathrm{-}}$, and ${\mathrm{Ra}}^{\mathrm{-}}$. This binding is due to a strong correlation potential acting between the electron and the neutral atom. Comparison with experimental data shows that the second order many-body perturbation theory calculation overestimates the correlation potential by 10% to 15%. Scaling factors are introduced in the correlation potential to reproduce experimental binding energies of the lower ${\mathrm{p}}_{1\mathrm{/}2}$ components. This procedure yields fine-structure intervals in excellent agreement with experiment for ${\mathrm{Ca}}^{\mathrm{-}}$, ${\mathrm{Sr}}^{\mathrm{-}}$, and ${\mathrm{Ba}}^{\mathrm{-}}$, and allows us to predict that in ${\mathrm{Ra}}^{\mathrm{-}}$ the ${\mathrm{p}}_{1\mathrm{/}2}$ state is bound by 100 meV, and ${\mathrm{p}}_{3\mathrm{/}2}$ is a resonance at 16 meV in the continuum.

The analytic result for the radiative correction of order ${\mathrm{\alpha }}^2$(Zα${)}^5$m to the Lamb shift connected with a polarization insertion in one of the two external Coulomb lines is obtained. This correction arises from a gauge-invariant set of diagrams which contain, besides the polarization insertion in the Coulomb leg, all one-loop radiative photon insertions in the electron line with two external Coulomb lines.

In the framework of a simple (atomic) model, already developed by other authors to compare ionization cross sections for diatomic molecules oriented with internuclear axis parallel or perpendicular to an ion beam, we have calculated the dependence of multi-ionization cross sections upon any relative orientation of the internuclear axis and the impinging ion direction. The results of our calculations are shown to fairly reproduce experimental data recently published about doubly ionized CO molecules. They suggest caution and increased attention to these orientation effects in the determination of kinetic energy distributions of fragments, dissociation fractions, and branching ratios for highly ionized molecules.

Based on the Hellman-Feynman theorem, it is shown that the average square radius of a cloud of interacting bosons in a parabolic well can be derived from their free energy. As an application, the temperature dependence of the moment of inertia of noninteracting bosons in a parabolic trap is determined as a function of the number of bosons. Well below the critical condensation temperature, the Bose-Einstein statistics are found to substantially reduce the moment of inertia of this system, as compared to a gas of ``distinguishable'' particles in a parabolic well.

A physical picture for spontaneous-emission cancellation or enhancement is developed.

We study the steady state in three-level lambda (Λ) and ladder systems. It is well known that in a Λ system this steady state is the coherent population trapping state, independent of the presence of spontaneous emission. In contrast, the steady state in a ladder system is in general not stable against radiative decay and exhibits a minimum in the population of the ground state. We show that incoherent population pumping destroys the stability of the coherent population trapping state in the Λ system and suppresses a previously discovered sharp dip in the steady-state response. In the ladder system the observed minimum disappears in the presence of an incoherent pump on the upper transition.

A weak continuous beam of a ${\mathrm{CO}}_2$ laser was used to probe the time changing gain and absorption inside the cavity of a passive Q-switching ${\mathrm{CO}}_2$ laser with ${\mathrm{SF}}_6$ gas in an intracavity saturable absorber cell. The probe variations detected simultaneously with the laser intensity pulses gave experimental projection planes of the chaotic system attractor.

Various three-level schemes for electromagnetic-field-induced control of absorption are analyzed to isolate the precise nature of the quantum interference. Such interference manifests through the dispersive contributions to the absorption line shapes. Depending on the excitation scheme, the dispersive terms can be either constructive or destructive. The collisional dephasing in some cases can change the nature of interference.