Photoelectron distributions of the polarized $2p^{5}3d$ Rydberg states of neon have been studied with a newly built velocity map imaging analyzer. The atoms were polarized by absorption of synchrotron radiation and ionized by an infrared laser. The asymmetry parameters ${\beta }_2$ and ${\beta }_4$ characterizing two-photon resonant ionization have been extracted from the measured images and compared with the results of a quantum defect treatment. To achieve a good theoretical description of the data, it is necessary to take into account the dependence of the dipole transition matrix elements and phases of the partial waves on the angular momentum quantum numbers pertaining to various continuum channels.

Three-particle dissociation of high-lying Rydberg states of ${\mathrm{H}}_3$, in the immediate vicinity of the ionization threshold, is induced by an external electric field. We observe that the momentum vector correlation map of the center-of-mass motion of the fragments changes rapidly with electronic energy. Near- and above-threshold substantial contributions of fragment orientations which are characteristic of near-linear geometry appear, i.e., two atoms with opposing momenta, the third atom being nearly at rest. This finding is similar to observations by Strasser et al. [Phys. Rev. A 66, 032719 (2002)], who studied dissociative recombination of cold ${\mathrm{H}}_3{}^{+}$ ions with slow electrons. We discuss the likely dissociation paths responsible for the observed correlation.

We consider radiative recombination and photoionization in an atomic system, which consists of two subsystems $A$ and $B$. These subsystems are well separated in space and it is supposed that $A$ has a lower ionization potential. In such a case photoionization of $A$ and recombination of an incident electron with $A^{+}$ can be strongly influenced, via two-center electron-electron correlations, by resonant electron dipole transitions induced in $B$. A theoretical description of these two-center resonant dielectronic processes is presented.

We study atomic autoionization processes in the time domain. With the emerging attosecond extreme vacuum ultraviolet and soft x-ray pulses, we first address how to characterize the time evolution of the decay of a discrete state into a degenerate continuum. A short pump beam generates a number of resonance states in a series and the nearby background continuum, and the resultant wave packet evolves with time until the full decay of the bound states. Taking the $2\mathit{pns}({}^1{P}^o)$ resonance series embedded in the $2s\epsilon p({}^1{P}^o)$ continuum in a beryllium atom as an example, the time evolution of the autoionizing wave packet in the energy domain and in coordinate space is calculated and analyzed, where Fano profiles build up in the photoelectron energy during the process. A proposed pump-probe scheme assumes that the probe beam ionizes the $2s$ inner electron in the wave packet. The lifetimes of the resonances and the photoelectron energy distribution can be obtained from the ionization yield vs. the time delay of the probe.

We demonstrate that the THz generation in air from a two-color pulse, composed of the fundamental and second-harmonic waves, can be coherently controlled by field-free molecular alignment. By tuning its time delay to properly match various molecular alignment revivals, the THz generation from the two-color pulse can be promoted or decreased due to the spatial cross-(de)focusing effect and the alignment-dependent ionization probabilities of the prealigned diatomic molecules in air. For the two-color pulse of orthogonally polarized fundamental and second-harmonic waves, the polarization of the generated THz radiation can be controlled by the field-free molecular alignment, which functions as a transient dynamic wave plate for the two-color pulse with different phase velocities for the orthogonally polarized field components. The plasma effect on the THz generation of the two-color pulse is also observed, leading to additional amplitude and polarization control of the THz radiation.

We use two-laser optical pumping on a continuous atomic fountain in order to prepare cold cesium atoms in the same quantum ground state. A first laser excites the $F=4$ ground state to pump the atoms toward $F=3$ while a second $\pi$-polarized laser excites the $F=3\to F^{\text{'}}=3$ transition of the $D_2$ line to produce Zeeman pumping toward $m=0$. To avoid trap states, we implement the first laser in a two-dimensional optical lattice geometry, thereby creating polarization gradients. This configuration has the advantage of simultaneously producing Sisyphus cooling when the optical lattice laser is tuned between the $F=4\to F^{\text{'}}=4$ and $F=4\to F^{\text{'}}=5$ transitions of the $D_2$ line, which is important to remove the heat produced by optical pumping. Detuning the frequency of the second $\pi$-polarized laser reveals the action of a mechanism improving both laser cooling and state-preparation efficiency. A physical interpretation of this mechanism is discussed.

The time-dependent Schrödinger equation for a two-dimensional model atom is solved exactly (numerically) for pulses of a circularly or linearly polarized strong laser field (in the dipole approximation). Although exact final ionization (or survival) probabilities do not depend on the choice of gauge, we show (both analytically and numerically) that ionization rates, calculated for a flat part of the strong laser pulse, may be gauge dependent. Differences between the length gauge and the velocity gauge ionization rates or survival probabilities (calculated through projections on “textbook” bound states) usually grow with an intensity of the laser field. The differences, which vanish in the limit of a weak field, may reach even a factor of 4 to the advantage of the length gauge for stronger fields. This fact points out that such a method of computing ionization rates may be not reliable in strong laser fields. Gauge-invariant ionization rates, calculated through a probability of finding an electron in a vicinity of a nucleus, usually have values being found between values of the previously mentioned gauge-dependent ionization rates.

Ultracold three-component atomic Fermi gases in one dimension are expected to exhibit rich physics due to the presence of trions and different pairing states. Quantum phase transitions from the trion state into a paired phase and a normal Fermi liquid occur at zero temperature. We derive the analytical thermodynamics of strongly attractive three-component one-dimensional fermions with SU(3) symmetry via the thermodynamic Bethe ansatz method in unequal Zeeman splitting fields $H_1$ and $H_2$. We find explicitly that for low temperature the system acts like either a two-component or a three-component Tomonaga-Luttinger liquid dependent on the system parameters. The phase diagrams for the chemical potential and specific heat are presented for illustrative values of the Zeeman splitting. We also demonstrate that crossover between different Tomonaga-Luttinger-liquid phases exhibit singular behavior in specific heat and entropy as the temperature tends to zero. Beyond Tomonaga-Luttinger-liquid physics, we obtain the equation of state which provides a precise description of universal thermodynamics and quantum criticality in three-component, strongly attractive Fermi gases.

We consider the dynamics of Bose-Einstein condensates in a corral-like potential. Compared to the electronic quantum corrals, the atomic quantum corrals have the advantages of allowing direct and convenient observation of the wave dynamics, together with adjustable interaction strength. Our numerical study shows that these advantages not only allow exploration of the rich dynamical structures in the density distribution but also make the corrals useful in many other aspects. In particular, the corrals for atoms can be arranged into a stadium shape for the experimental visualization of quantum chaos, which has been elusive with electronic quantum corrals. The density correlation is used to describe quantitatively the dynamical quantum chaos. Furthermore, we find that the interatomic interaction can greatly enhance the dynamical quantum chaos, for example, inducing a chaotic behavior even in circle-shaped corrals.

We study the dynamics of fast soliton collisions in a Kerr nonlinear optical waveguide with weak cubic loss. We obtain analytic expressions for the amplitude and frequency shifts in a single two-soliton collision and show that the impact of a fast three-soliton collision is given by the sum of the two-soliton interactions. Our analytic predictions are confirmed by numerical simulations with the perturbed nonlinear Schrödinger (NLS) equation. Furthermore, we show that the deterministic collision-induced dynamics of soliton amplitudes in a broadband waveguide system with $N$ frequency channels is described by a Lotka-Volterra model for $N$ competing species. For a two-channel system we find that stable transmission with equal prescribed amplitudes can be achieved by a proper choice of linear amplifier gain. The predictions of the Lotka-Volterra model are confirmed by numerical solution of a perturbed coupled-NLS model.

High-order harmonic generation (HHG) has been studied in various laser-produced plasma plumes using a two-color orthogonally polarized beam with a 12:1 energy ratio between the fundamental and second-harmonic (SH) components. The influence of the relative phase between the fundamental and SH waves on the HHG efficiency has been investigated. Odd and even harmonic generation in plasma plumes containing nanoparticles, fullerenes, carbon nanotubes, and other samples was optimized. The effect of the variation in the SH intensity on the HHG conversion efficiency in carbon aerogel and silver plasma plumes has also been studied. It is shown that by increasing the SH intensity, one can generate only even harmonics by suppressing the odd harmonics.

The realization of a Jaynes-Cummings model in the optical domain is proposed for an atomic ensemble. The scheme exploits the collective coupling of the atoms to a quantized cavity mode and the nonlinearity introduced by coupling to high-lying Rydberg states. A two-photon transition resonantly couples the single-atom ground state $|g\rangle$ to a Rydberg state $|e\rangle$ via a nonresonant intermediate state $|i\rangle$, but due to the interaction between Rydberg atoms only a single atom can be resonantly excited in the ensemble. This restricts the state space of the ensemble to the collective ground state $|G\rangle$ and the collectively excited state $|E\rangle$ with a single Rydberg excitation distributed evenly on all atoms. The collectively enhanced coupling of all atoms to the cavity field with coherent coupling strengths which are much larger than the decay rates in the system leads to the strong coupling regime of the resulting effective Jaynes-Cummings model. We use numerical simulations to show that the cavity transmission can be used to reveal detailed properties of the Jaynes-Cummings ladder of excited states and that the atomic nonlinearity gives rise to highly nontrivial photon emission from the cavity. Finally, we suggest that the absence of interactions between remote Rydberg atoms may, due to a combinatorial effect, induce a cavity-assisted excitation blockade whose range is larger than the typical Rydberg dipole-dipole interaction length.

We present an investigation of the interaction of solitons in dispersion-managed fibers beyond the regime of formation of stable pairs (soliton molecules). There is a nonlinear resonance between a slow (compared to the dispersion map period) oscillation of the pulse shape and the typical distance of bouncing of the pulses off each other. Parameter ranges for either repetitive bouncing or a final split of the pair are shown to be organized in a self-similar pattern. Predictions of a theoretical model agree well with numerical simulations.

We explore theoretically the phase correlation between multiple generated sidebands in a Raman optical frequency comb under conditions of spontaneous initiation from quantum zero-point noise. We show that there is a near-deterministic correlation between sideband phases in each laser shot which may lead to synthesis of attosecond pulse trains.

A detailed derivation of the master equation and the corresponding time evolution of the cavity radiation of a coherent beat laser when the atoms are initially prepared in a partial coherent superposition is presented. It turns out that the quantum features and intensity of the cavity radiation are considerably modified by the phase fluctuation arising due to the practical incapability of preparing atoms in the intended perfect coherent superposition. New terms having opposite signs than the contribution of the driving radiation emerged in the master equation. This can be taken as an indication of a competing effect between the two in the manifestation of the nonclassical features. This, on the other hand, means that there is a chance to regain the quantum properties that might have been lost due to faulty preparation in engineering the driving mechanism and vice versa. In light of this, quite remarkably, the cavity radiation is shown to exhibit nonclassical features including two-mode squeezing and entanglement when there is no driving and when the atoms are initially prepared in a partial maximum atomic coherence superposition, contrary to earlier predictions for the case of perfect coherence.

We investigate the transport properties of two photons inside a one-dimensional waveguide side-coupled to a single-mode nonlinear cavity. The cavity is filled with a nonlinear Kerr medium. Based on the Laplace transform method, we present an analytic solution for the quantum states of the two transmitted and reflected photons, which are initially prepared in a Lorentzian wave packet. The solution reveals how quantum correlation between the two photons emerges after the scattering by the nonlinear cavity. In particular, we show that the output wave function of the two photons in position space can be localized in relative coordinates, which is a feature that might be interpreted as a two-photon bound state in this waveguide-cavity system.

We report an experimental demonstration of generating gap soliton trains in a four-wave-mixing (FWM) signal. Such spatial FWM surfacelike gap soliton trains are induced in a periodically modulated self-defocusing atomic medium by the cross-phase modulation, which can be reshaped under different experimental conditions, such as different atomic densities, nonlinear dispersions, and dressing fields. Controlling spatial gap solitons can have important applications in image memory, processing, and communication.

The concept of an active drain has been used recently to provide an optical element which manages to perfectly sink incoming electromagnetic radiation. Here I show that, without prior knowledge of the incoming signal, an element attempting to respond as an active localized drain cannot succeed.

In a recent article [Phys. Rev. A 81, 032901 (2010)] a theory of light-induced atomic desorption for Rb in porous alumina is proposed. We point out that both the main assumption of this theory (the diffusion inside the pores treated as a random walk with the adsorption to the inner surface of the pores at any step) and several further hypotheses supporting the theoretical model require a revision.

We argue that the model used in our paper [Phys. Rev. A 81, 032901 (2010)] for the analysis of the experimental study of light-induced atomic desorption in porous alumina is the simplest consistent approach to a previously unexplored physical system.