In this work, we present a theoretical study of the origin of the spatial structures in the conventional magneto-optical trap by using a numerical model based on the solutions of the equations of motion of trapped atoms, in the limit where the radiation trapping force is not relevant. Some results relating to the comparison between the experimental and theoretical data are reported. Also, we show that this same analysis can be employed to describe the spatial structures formation in atomic beams.

The threshold for H atom ionization by circularly polarized microwave fields is discussed within the classical mechanics framework for high microwave frequencies. The Chirikov resonance overlap criterion predictions are compared with estimates obtained adopting the renormalization method. It is shown that the ionization threshold is highly sensitive to the helicity of microwaves. Among all possible initial electronic orbits, those of medium eccentricity are the first to ionize. The results obtained indicate that collisions with the nucleus play a negligible role for the onset of ionization.

A semiclassical approach to ionization by an oscillating field is presented. An asymptotic analysis is performed with respect to a quantity h, defined (up to a factor) as the ratio of photon energy to ponderomotive energy. This h appears formally equivalent to Planck's constant in a suitably transformed Schrödinger equation and allows us to formally use semiclassical methods. Systematically, a picture of tunneling wave packets in complex time is developed, which by interference account for the typical ponderomotive features of ionization curves. For a one-dimensional δ-function atom, these analytical results are compared to numerical simulations [Scharf, Sonnenmoser, and Wreszinski, Phys. Rev. A 44, 3250 (1991)] and are shown to be in good agreement.

Laser-controlled ultrafast state-selective vibrational dynamics of diatomic molecules, which are coupled to an unobserved quasiresonant environment is investigated using the reduced density-matrix formalism beyond and within a Markov-type approximation. Dissipative quantum dynamics in a classical electric field of shaped infrared ultrashort laser pulses is simulated for a one-dimensional nondissociative Morse oscillator, representing the local OH bond in the ${\mathrm{H}}_2$ O and HOD molecules in the electronic ground state. Localization of population at a prescribed vibrational target level of OH up to v=10 with probability of about 90% is demonstrated on a picosecond time scale, while the strength of the quasiresonant molecule-environment coupling results in subpicosecond lifetimes of the vibrational states. The laser-controlled stabilization of selective excitation in the restricted set of vibrational states against a background of strongly diminished relaxation to lower vibrational states is also shown. The laser-control scheme may include a superposition of several laser pulses. A Markov-type approximation results in slightly increased lifetimes of the vibrational states, along with decreased predicted probability of state-selective excitation of a molecule by about 20–30%. Several results obtained within the fourth-order perturbation theory in interaction of a molecule with an environment are in a good agreement with the non-Markov analysis.

We have developed a diagnostic tool for the study of Zeeman-compensated slowing of an alkali-metal atomic beam. Our time-of-flight technique measures the longitudinal velocity distribution of the slowed atoms with a resolution below the Doppler limit. Furthermore, it can map the position and velocity distribution of atoms in either ground hyperfine level inside the solenoid without any devices inside the solenoid. The technique reveals the optical pumping effects and shows in detail how the slowing within the solenoid proceeds. We find for Na that most atoms in the chosen hyperfine state are decelerated in the slowing process. The width of the velocity distribution is determined mainly by inhomogeneities in the slowing laser beam. Using the central most uniform part of an expanded laser beam, the width is reduced to 2.5 m/s, corresponding to 3.2 mK. Finally, we discuss and show a method to produce a beam with two-velocity components for the study of head-tail low-energy collisions.

Harmonic generation is studied in an idealized model medium in which the laser field essentially interacts only with a single atomic transition and where ionization can be neglected. Such two-level models are known to generate high harmonics with a plateau and a cutoff. We put forward a quantitative rule for the cutoff frequency in the harmonic spectrum in this model which we relate to the ``${\mathrm{I}}_{\mathrm{P}}$+${3\mathrm{U}}_{\mathrm{P}}$ rule'' in real systems with ionization. We examine the phase properties of the emitted harmonics and show that their coherence and thus phase matching is more favorable in the cutoff regime than in the plateau of the harmonic spectrum. This behavior is known to occur in realistic models of neon, and that this occurs also for the simple idealized two-level model strongly suggests that the sudden change of phase coherence from the cutoff to the plateau regime is as intrinsic a property of nonlinear systems as are the plateau and the cutoff.

A soluble model of electromagnetic field interacting with time-dependent dielectric medium is given. The main assumption is that the dielectric constant is switched rapidly from the initial to the final value. Generation of electromagnetic field and photon statistics are found.

Photoionization of the circular 5g Rydberg state in neon by an intense subpicosecond light pulse is studied. Both the photoionization yield and the remaining population are measured. We find that the photoionization yield does not increase when the pulse peak intensity is increased above 60 TW/${\mathrm{cm}}^2$, and that a large fraction of the population remains in the 5g state instead. These results are consistent with predictions for adiabatic stabilization. The measurements are done using a sequence of three laser pulses. The first laser pulse excites the circular 5g state from the neon ground state, the second pulse is the intense light pulse that leads to the ionization (or lack thereof due to stabilization) we actually study, and the third pulse is a low-intensity high-fluence pulse ionizing all of the remaining 5g population. The photoionization yields of these three pulses are detected and separated by electron spectroscopy.

We propose a scheme for generating SU(1,1) intelligent states for the quantized vibrational motion of a trapped ion. The SU(1,1) intelligent states are those states satisfying the equalized SU(1,1) uncertainty relation. The relevant operators can be realized for one or two vibrational modes (the states for the latter having strong intermode correlations) and we consider both cases. In the single-mode case, three codirectional laser beams are used to excite the trapped ion, while for the two-mode case, five laser beams along different directions in the X-Y plane of the ion trap are required. Our desired states are obtained as the steady-state solutions, indicated by the extinction of the fluorescence by the ion, of the master equation containing dissipative terms due to spontaneous emission with appropriately chosen initial states. The system is also studied numerically using a Monte Carlo state-vector method.

We observe a shape resonance in the scattering of two ultracold ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ atoms, causing the colliding atoms to form a long-living compound system inside an l=2 centrifugal barrier. Its existence follows from a photoassociation experiment in a gas sample of doubly polarized ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ atoms. Using it we are able to carry out direct determinations of the triplet scattering length for ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$, relevant to Bose-Einstein condensation experiments, and of the Rb+Rb ${\mathrm{C}}_6$ dispersion coefficient. Consequences for the ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$ scattering length are discussed.

A theory of high-energy electron diffraction from diatomic molecular gases after excitation by a femtosecond laser is presented. Rotational and vibrational coherence created by the excitation pulse are taken into account. The use of the spherical tensor components of the density matrix along with the Liouville space formalism allows a systematic derivation of the resulting equations.

We demonstrate that various properties of population transfer by delayed pulses in three-level systems on two-photon resonance can be deduced analytically and for general pulse shapes. We use the fact that the three-level system reduces to effective two-level problems at large intermediate-level detuning Δ, on resonance (Δ=0) and for completely overlapping pulses. Special attention is paid to the effect of the pulse order on the population transfer efficiency. We show that on resonance the transfer efficiency depends substantially on the pulse order, while at large Δ it does not. We also find that under some natural restrictions on the symmetry of the problem, the population of the initial level does not depend on the pulse order at any Δ. Furthermore, we demonstrate that the population transfer in the three-level system can be viewed as a level-crossing problem in an equivalent two-level system not only at large Δ (which is known) but also on resonance, Δ=0. The effective on-resonance two-level problem is interesting by itself as it shows that a level crossing and adiabatic evolution do not necessarily lead to complete population inversion. As examples throughout the paper, we present several analytically solvable models.

Continuous-wave generation of an anti-Stokes Raman laser on a number of blue-green argon-ion lines (4p-4s and 4p-3d) has been demonstrated with optical pumping from metastable levels ${3\mathrm{d}}^{|\mathrm{I}\mathrm{H}2\mathrm{}}$G and ${3\mathrm{d}}^4$F. It is found that the population transfer rate is increased by a factor of 3–5 (and hence the output power of the Raman laser) owing to Coulomb diffusion in the velocity space. The excitation and relaxation rates for the metastable level have been measured. The Bennett hole on the metastable level has been recorded using the probe field technique. It has been shown that Coulomb diffusion changes the shape of the contour to an exponential cusplike profile. Its width exceeds the Lorentzian one by 100 times and is close to the Doppler width. Such a giant broadening is also confirmed by the shape of the absorption saturation curve.

We present an experimental study of cw degenerate four-wave mixing (DFWM) in Doppler-broadened rubidium atoms coupled by an additional coherent field. The coupling field and the DFWM fields were arranged in a Λ-type configuration from the rubidium ${\mathrm{D}}_2$ transitions. We found that the presence of the coherent coupling field modifies the DFWM emission:mfat lower intensities of the coupling field, the DFWM emission is enhanced; at higher intensities of the coupling field, the DFWM is reduced. The observed effect of the coupling laser on the DFWM emission may be explained by the direct competition between the resonance-enhanced two-photon Raman scattering and the optical-pumping-enhanced DFWM emission.

We present a quantum error correcting code that is invariant under the conditional time evolution between spontaneous emissions and which can correct for one general error. The code presented here generalizes previous error correction codes in that not all errors lead to different error syndromes. This idea may lead to shorter codes than previously expected.

This paper considers the feasibility of creating dispersion-free solitary quantum-mechanical wave packets. The analysis is carried out within a general framework of quantum-optimal control theory. A key to the realization of solitary quantum wave packets is the ability to create traveling wave potentials U(x-νt) with coordinated space and time dependence where ν is a characteristic speed. As an illustration, the case of an atom translating in a designed optical trap is considered. Three examples are treated within this framework: (A) the motion of a dispersion-free traveling bound state, (B) feedback-stabilized solitonic motion, and (C) feedback-stabilized solitonic motion in the presence of auxiliary physical objectives. The quantum solitons of (B) and (C) satisfy a nonlinear Schrödinger-type equation with laboratory feedback in the form of an observation of the probability density. This feedback is essential for maintaining the solitonic-type motion. Some generalizations and potential applications of these concepts are also discussed.

Theories which have been used to describe the quantized electromagnetic field interacting with a nonlinear dielectric medium are either phenomenological or derived by quantizing the macroscopic Maxwell equations. Here we take a different approach and derive a Hamiltonian describing interacting fields from one which contains both field and matter degrees of freedom. The medium is modeled as a collection of two-level atoms, and these interact with the electromagnetic field. The atoms are grouped into effective spins and the the Holstein-Primakoff representation of the spin operators is used to expand them in inverse powers of the total spin. When the lowest order term of the interaction is combined with the free atomic and field Hamiltonians, a Hamiltonian describing a theory of noninteracting polaritons results. When higher order terms are expressed in terms of polariton operators standard nonlinear optical interactions emerge. These are then compared to the results of phenomenological and macroscopic theories. The theory is also used to derive an effective Hamiltonian describing counterpropagating modes in a nonlinear medium.

We show that an index—and gain—guided vertical-cavity surface-emitting laser with a square-shaped active region can operate as a bistable laser with the two Gauss-Hermite modes ${\mathrm{TEM}}_{10}$ and ${\mathrm{TEM}}_{01}$. Optical switching from one mode to the other upon injection of appropriate Gaussian pulses is numerically investigated; the switching energy can be as small as 30 fJ and the process is completed in a time of the order of a few nanoseconds. We demonstrate the possibility of using the laser as a logic gate of the NOR, OR, NOT type. Carrier diffusion increases laser threshold and the size of the bistability domain, and it reduces both switching time and switching energy.

The generation of Schrödinger-cat-like states for quantum fundamental solitons in optical fibers is investigated. It is shown that the generation is possible at proper times in the dynamical evolution of an appropriately chosen initial state. Such a Schrödinger-cat-like state has a minimum number of components, three, and the superposition coefficients of components are all real. Mean values of the field and the intensity operators are calculated and the associated quantum interference behavior characteristic of quantum coherent superposition in the Schrödinger-cat-like states is revealed. The effect of dissipation on the Schrödinger-cat-like states is analyzed using a beam splitter. The severity with which losses tend to destroy interference between components of the input Schrödinger-cat-like state is noted.

A scheme which results in the simultaneous narrowing of all three spectral peaks of the Mollow triplet is proposed. In particular, we investigate the effect on resonance fluorescence of processing the squeezed output of an optical parametric oscillator by propagation through a linear dielectric. The frequency-dependent squeezing phase induced by this process is found to result in subnatural spectral widths for appropriate parameter choices. The line-narrowing mechanisms at the Rabi sidebands manifest themselves in the second-order correlation function of the fluorescent field which is found to decay at a subnatural rate. The potential for experimental realization of these phenomena is discussed.