This paper reports on the investigation of the double $K$-shell ionization of metallic aluminum induced by photon and electron impact. The experimental method consisted to measure the $K\alpha$ hypersatellite spectra resulting from the radiative decay of double $1s$ vacancy states by means of high-resolution x-ray spectroscopy using a Bragg-type von Hamos crystal spectrometer. Measurements of the photon-induced spectra were carried out at the European Synchrotron Radiation Facility, Grenoble, France, while those of the electron-induced spectra were performed at the University of Fribourg. The double $1s$ ionization probabilities and cross sections were derived from the $K{\alpha }_2$ hypersatellite to diagram line intensity ratios for photon beam energies ranging between 3.1 and 5.5 keV and for different incident electron-beam energies ranging between 4 and 20 keV. The energy and linewidth of the $K{\alpha }_2$ hypersatellite x-ray line were also determined for which consistent results were obtained from the photon and electron-beam measurements.

Based on a quantum-mechanical model, we calculate the time evolution of an initial nuclear vibrational wave packet in $\text{D}_2{}^{+}$ generated by the rapid ionization of ${\text{D}}_2$ in an ultrashort pump-laser pulse. By Fourier transformation of the nuclear probability density with respect to the time delay between the pump pulse and the instant destructive Coulomb-explosion imaging of the wave packet at the high-intensity spike of an intense probe-laser pulse, we provide two-dimensional internuclear-distance-dependent power spectra that serve as a tool for visualizing and analyzing the nuclear dynamics in $\text{D}_2{}^{+}$ in an intermittent external laser field. The external field models the pedestal to the central ultrashort spike of a realistic probe pulse. Variation in the intensity, wavelength, and duration of this probe-pulse pedestal (i) allows us to identify the optimal laser parameters for the observation of field-induced bond softening and bond hardening in $\text{D}_2{}^{+}$ and (ii) suggests a scheme for quantitatively testing the validity of the “Floquet picture” that is commonly used for the interpretation of short-pulse laser-molecule interactions, despite its implicit “continuum wave” (infinite pulse length) assumption.

We investigate the connection of recently identified fine-scale oscillations in the dependence of the yield of the high-order harmonic generation (HHG) on wavelength $\lambda$ of a few-cycle laser pulse [K. Schiessl et al., Phys. Rev. Lett. 99, 253903 (2007)] to the well-known channel-closing (CC) effect. Using the Lewenstein model of HHG, we identify the origin of the oscillations as quantum interference of many rescattering trajectories. By studying the simultaneous variations with intensity and wavelength, different models for the interference of channel-closing peaks can be tested. Contrary to theoretical predictions for short-range potentials, the peaks are located neither at nor just below the CC condition, but a significant shift is observed. The long Coulomb tail of the atomic potential is identified as the origin of the shift.

We propose a different type of Landau instability in trapped Bose-Einstein condensates by a helically moving environment. In the presence of quantized vortices, the instability can cause spontaneous radiation and amplification of Kelvin waves. This study gives a microscopic understanding of the Donnelly-Glaberson instability which was known as the hydrodynamic instability in superfluid helium. The Donnelly-Glaberson instability can be a powerful tool for observing the dispersion relation of Kelvin waves, vortex reconnections, and quantum turbulence in atomic Bose-Einstein condensates.

We study the implementation of a correlation measurement technique for the characterization of squeezed light which is nearly free of electronic noise. With two different sources of squeezed light, we show that the sign of the covariance coefficient, revealed from the time-resolved correlation data, is witnessing the presence of squeezing in the system. Furthermore, we estimate the degree of squeezing using the correlation method and compare it to the standard homodyne measurement scheme. We show that the role of electronic detector noise is minimized using the correlation approach as opposed to homodyning where it often becomes a crucial issue.

The analysis of an angular distribution of the emission intensity of a two-level atom (dipole) in a photonic crystal reveals an enhancement of the emission rate in some observation directions. Such an enhancement is the result of the bunching of many Bloch eigenwaves with different wave vectors in the same direction due to the crystal anisotropy. If a spatial distribution of the emission intensity is considered, the interference of these eigenwaves should be taken into account. In this paper, the far-field-emission pattern of a two-level atom is discussed in the framework of the asymptotic analysis of the classical macroscopic Green’s function. Numerical example is given for a two-dimensional square lattice of air holes in polymer. The relevance of results for experimental observation is discussed.

Single-photon sources (SPSs) are mainly characterized by the minimum value of their second-order coherence function, viz. their $g^{\left(2\right)}$ function. A precise measurement of $g^{\left(2\right)}$ may, however, require high time-resolution devices, in whose absence, only time-averaged measurements are accessible. These time-averaged measures, standing alone, do not carry sufficient information for proper characterization of SPSs. Here, we develop a theory, corroborated by an experiment, which allows us to scrutinize the coherence properties of heralded SPSs that rely on continuous-wave parametric down conversion. Our proposed measures and analysis enable proper standardization of such SPSs.

We investigate the classical capacity of two quantum channels with memory: a periodic channel with depolarizing channel branches and a convex combination of depolarizing channels. We prove that the capacity is additive in both cases. As a result, the channel capacity is achieved without the use of entangled input states. In the case of a convex combination of depolarizing channels the proof provided can be extended to other quantum channels whose classical capacity has been proven to be additive in the memoryless case.

Bound and resonance states of a two-electron quantum dot are studied using a variational expansion with real basis-set functions. The two-electron entanglement (von Neumann entropy) is calculated as a function of the quantum-dot size at both sides of the critical size, where the ground (bound) state becomes a resonance (unbound) state. The use of von Neumann entropy is proposed as a method for the determination of the energy of a resonance.

Accurate calculations of the fine and hyperfine splitting of the $2P$ state in Li and ${\text{Be}}^{+}$ isotopes using the explicitly correlated Hylleraas basis set are presented. Theoretical predictions including the mixing of $P_{1/2}$ and $P_{3/2}$ states, relativistic and quantum electrodynamic effects on hyperfine interactions, are compared with experimental values. It is concluded that precise spectroscopic determination of the nuclear magnetic moments requires elimination of nuclear structure effects by combining measurements for two different states.

Rate constants for dissociative electron attachment to ${\text{Cl}}_2$ have been measured from 300 to 1100 K in a high-temperature flowing-afterglow Langmuir-probe apparatus. $R$-matrix calculations have been carried out which compare well with the present measurements with possible deviation at the highest temperatures. The attachment rate constants do not show Arrhenius behavior. The temperature dependence of the calculated rate constants for successive vibrational levels provides insight as to this behavior. While the lowest vibrational level of ${\text{Cl}}_2$ dominates attachment at low temperatures, the rate constant is not flat with temperature because of the $p$-wave character of the attachment process. The non-Arrhenius behavior is due to a conflict between the increase in attachment cross section with vibrational level (temperature) and the decline in the cross section with electron energy above 50 meV.

The comparative study on the geometric and energetic properties, absorption spectra, and polarizabilities of cagelike ${\text{CuSi}}_n$ clusters ($n=9–14$; indicated by $\text{Cu}@{\text{Si}}_n$) was performed using the density-functional theory. The influence of a charge on these properties was investigated. The charge has more effect on the geometry of $\text{Cu}@{\text{Si}}_n$ ($n=9$, 11, and 13) than $\text{Cu}@{\text{Si}}_n$ ($n=10$, 12, and 14). For $n=10–13$, the charge directly leads the neutral geometry to the transition state geometry with one imaginary frequency. The influence of a charge on the overall and relative stabilities of the neutral and charged $\text{Cu}@{\text{Si}}_n$ clusters was analyzed based on the binding energy, energy gap, adiabatic electron affinity, adiabatic ionization potential, and second-order energy difference. The charge slightly increases the binding energy by about 0.13 eV. For the charged clusters, those with $n=10$, 12, and 14 still have a higher relative stability than those with $n=9$, 11, and 13. In the visible range, the shape of the absorption spectra is not influenced by a charge. However, the charge results in a blueshift of the absorption spectra. The order of $\text{anion}>\text{neutral}>\text{cation}$ for the static isotropic polarizabilities does not apply to the dynamic isotropic polarizabilities at some optical-field frequencies due to the one-photon resonance, which is based on the absorption spectra and the sum-over-states formula of the polarizabilities. The charge significantly affects the static anisotropic polarizabilities because the charge influences the geometry of the clusters. The charge also influences the resonant behavior of the dynamic polarizabilities due to its effect on the absorption spectra.

We employed electron-ion coincidence momentum spectroscopy to measure the relative angle between an emitted electron and a deuteron resulting from field dissociation of the molecular ion produced by a circularly polarized pulse. We deduced the angular dependence of the molecular ionization probability without having to align the molecules first. We determined that with 50 fs pulses of 1850 nm wavelength and $2\times {10}^{14}\text{W}/{\text{cm}}^2$ intensity neutral ${\text{D}}_2$ molecules are 1.15 times more likely to be ionized when the laser electric field is parallel to the molecular axis than for the perpendicular orientation, in excellent agreement with our ab initio theoretical model. Our results also agree with predictions of the molecular Ammosov-Delone-Krainov (mo-ADK) theory, as well as those of a similar experiment performed with 800 nm pulses of comparable intensity and duration on ${\text{H}}_2$ molecules.

A comprehensive quantitative rescattering (QRS) theory for describing the production of high-energy photoelectrons generated by intense laser pulses is presented. According to the QRS, the momentum distributions of these electrons can be expressed as the product of a returning electron wave packet with the elastic differential cross sections (DCS) between free electrons with the target ion. We show that the returning electron wave packets are determined mostly by the lasers only and can be obtained from the strong field approximation. The validity of the QRS model is carefully examined by checking against accurate results from the solution of the time-dependent Schrödinger equation for atomic targets within the single active electron approximation. We further show that experimental photoelectron spectra for a wide range of laser intensity and wavelength can be explained by the QRS theory, and that the DCS between electrons and target ions can be extracted from experimental photoelectron spectra. By generalizing the QRS theory to molecular targets, we discuss how few-cycle infrared lasers offer a promising tool for dynamic chemical imaging with temporal resolution of a few femtoseconds.

Recent progress in the field of ultracold gases has allowed for the creation of phase-segregated Bose-Fermi systems. We present a theoretical study of their collective excitations at zero temperature. As the fraction of fermion-to-boson particle number increases, the collective mode frequencies take values between those for a fully bosonic and those for a fully fermionic cloud, with damping in the intermediate region. This damping is caused by fermions which are resonantly driven at the interface.

We propose a time-dependent three-dimensional numerical model which successfully explains the complex spatiotemporal dynamic of photorefractive self-focusing of an infrared beam in InP:Fe. Characteristic behaviors are in good agreement with experiments previously reported. Intensity dependence and asymmetric photoinduced index profile are explained. In addition self-trapping dynamics shows potential self-trapping response in the microsecond range.

The number of Maxwell-Bloch equations describing the spatiotemporal evolution of solid-state and semiconductor-based lasers can be reduced when the temporal scales of the fields and atomic variables are very different. We demonstrate the existence of slow (center) manifolds for models of solid-state lasers (such as Nd:YAG) and vertical-cavity surface-emitting lasers and determine reduced equations in the presence of both diffraction and carrier diffusion. Two separate methods of obtaining the reduced equations are presented. Excellent agreement between the reduced models and the original equations is obtained when the slow manifolds are expanded in a perturbative series. Since stiffness is removed, the computational time for the long-term spatiotemporal dynamics of these devices can be strongly reduced, typically by 2 orders of magnitude.

We show the possibility to generate bright and dark optical solitons based on bound-to-bound intersubband transitions in an asymmetric three-coupled quantum well structure. By presenting the concept of detuning management, we show that the bright optical soliton can evolve into a dark one by adiabatically changing the corresponding one- and two-photon detunings. With adjustable carrier frequencies within the terahertz regime, we also demonstrate numerically shape-recovered collisions of two solitons in our proposed quantum wells. The present investigation may provide research opportunities in nonlinear optical experiments and may have impact on the technology for the design of semiconductor devices.

We consider propagation of a weakly nonlinear probe light beam in a resonant three-level atomic system where an optical lattice is induced by a standing-wave control field and conditions for electromagnetically induced transparency are created. We employ a unified theory to solve the respective nonlinear system of equations in various regimes and investigate formation of spatial optical solitons and instabilities, both analytically and numerically. We show that the effect of the lattice is twofold. On the one hand it allows one to reduce the probe beam intensity necessary for observation of nonlinear effects until the level of one-photon energy, and on the other hand the lattice allows for implementation of different dynamical regimes either by simple manipulation of its parameters or by varying one- and two-photon detunings or by changing the geometry of the incident probe beam.

A practical scheme is proposed for the creation of continuous-variable entangled cluster states of four distinct atomic ensembles located inside a high-finesse ring cavity. The scheme does not require a set of external input squeezed fields, a network of beam splitters, and measurements. It is based on nothing else than the dispersive interaction between the atomic ensembles and the cavity mode and a sequential application of laser pulses of a suitably adjusted amplitudes and phases. We show that the sequential laser pulses drive the atomic “field modes” into pure squeezed vacuum states. The state is then examined against the requirement to belong to the class of cluster states. We illustrate the method on three examples of the entangled cluster states: the so-called continuous-variable linear, square, and T-type cluster states.