Tensor properties of the nonlinear-optical response of an ionized atmospheric air are studied by polarization analysis of the four-wave mixing of high-intensity infrared femtosecond laser pulses. Results of these experiments are consistently explained in terms of an isotropic Kleinmann-symmetric cubic nonlinear susceptibility ${\chi }^{\left(3\right)}$ tensor, suggesting that the nonlinear-optical response of an ionized air within the studied range of field intensities is isotropic and features no or a very weak dispersion within the range of wavelengths from 800 to 1400 nm.

We perform an ab initio study of multiphoton ionization (MPI) of carbon dioxide in intense linearly polarized laser pulses with arbitrary molecular orientation by means of a time-dependent density-functional theory (TDDFT) with proper long-range potential. We develop a time-dependent Voronoi-cell finite difference method with highly adaptive molecular grids for accurate solution of the TDDFT equations. Our results demonstrate that the orientation dependence of MPI is determined by multiple orbital contributions and that the electron correlation effects are significant. The maximum peak of MPI is predicted to be at $40°$ in good agreement with recent experimental data. Photoelectron angular distribution reveals the delicate relation between the orientation dependence and the molecular orbital symmetry.

The pushing of the modes of a Fabry-Perot cavity by an intracavity rubidium cell is measured. The scale factor of the modes is increased by the anomalous dispersion and is inversely proportional to the sum of the effective group index and an additional cavity delay factor that arises from the variation of the Rb absorption over a free spectral range. This additional positive feedback further increases the effect of the anomalous dispersion and goes to zero at the lasing threshold. The mode width does not grow as fast as the scale factor as the intracavity absorption is increased resulting in enhanced measurement sensitivities. For absorptions larger than the scale factor pole, the atom-cavity response is multivalued and mode splitting occurs.

We report on theoretical calculations and experimental observations of Pancharatnam’s phase originating from arbitrary SU(2) transformations applied to polarization states of light. We have implemented polarimetric and interferometric methods, which allow us to cover the full Poincaré sphere. As a distinctive feature, our interferometric array is robust against mechanical and thermal disturbances, showing that the polarimetric method is not inherently superior over the interferometric one, as previously assumed. Our strategy effectively amounts to feeding an interferometer with two copropagating beams that are orthogonally polarized with respect to each other. It can be applied to different types of standard arrays, such as a Michelson, a Sagnac, or a Mach-Zehnder interferometer. We exhibit the versatility of our arrangement by performing measurements of Pancharatnam’s phases and fringe visibilities that closely fit the theoretical predictions. Our approach can be easily extended to deal with mixed states and to study decoherence effects.

In this paper, we propose to use the decoy-state technique to improve the security of the quantum key distribution (QKD) systems based on homodyne detection against the photon number splitting attack. The decoy-state technique is a powerful tool that can significantly boost the secure transmission range of the QKD systems. However, it has not yet been applied to the systems that use homodyne detection. After adapting this theory to the systems based on homodyne detection, we quantify the secure performance and transmission range of the resulting system.

The interacting and the Kohn-Sham static density-density response functions for different one-dimensional two-electron singlet systems are reconstructed numerically. From their inverse we obtain the exact static exchange-correlation kernel. This quantity represents the adiabatically exact approximation of the frequency-dependent exchange-correlation kernel that is crucial for time-dependent linear density-response theory. We investigate its performance for nonlocal perturbations and analyze its sum rule properties. We also compute the adiabatically exact transition energies that follow from the static kernel within linear-response theory.

The charge transfer in collisions of ${\text{C}}^{2+}$ ions with the CO molecule and the OH radical has been studied theoretically by means of ab initio quantum chemistry molecular methods followed by a semiclassical dynamical treatment in the keV collision energy range. The comparison of the cross sections calculated for these two collision systems exhibits interesting features with regard to the anisotropy of these processes and the influence of the vibration of the molecular target.

The dissociative electron attachment (DEA) process in electron-${\text{H}}_2$ molecule collisions, involving the ${{}^2\Sigma }_g^{+}$ excited electronic Rydberg state of molecular hydrogen ion $\text{H}_2{}^{-}$, is investigated theoretically. The DEA cross section has been calculated within the local complex potential approximation. The convoluted cross section, which presents a peak located at the incident energy of about 14 eV, compares favorably with available experimental data.

Ionization of highly charged relativistic ions by neutral atoms and ions is considered. Numerical results of recently developed computer codes based on the plane-wave Born and the equivalent-photon approximations are presented and compared with experimental data available at relativistic energies for $1s$ electron ionization. New formulas for relativistic cross sections are derived for ionization of the projectile electron with arbitrary quantum numbers $n$ and $l$. The results are obtained on the basis of the nonrelativistic reduction in the Dirac matrix element.

We show theoretically that a vacuum-clad silica-core fiber can focus a perpendicularly incident light onto one or several lines parallel to the fiber axis. We demonstrate numerically that such a focusing action of the fiber can be used to trap and to guide atoms along the fiber with a red- or a blue-detuned incident light.

Spin-exchange relaxation free alkali-metal magnetometers typically operate in the regime of high optical density, presenting challenges for simple and efficient optical pumping and detection. We describe a high-sensitivity Rb magnetometer using a single elliptically polarized off-resonant laser beam. Circular component of the light creates relatively uniform spin polarization while the linear component is used to measure optical rotation generated by the atoms. Modulation of the atomic spin direction with an oscillating magnetic field shifts the detected signal to high frequencies. Using a fiber-coupled distributed feedback laser, we achieve magnetic field sensitivity of $7\text{fT}/\sqrt{\text{Hz}}$ with a miniature $5\times 5\times 5\text{mm}\text{Rb}$ vapor cell.

The optical vortices that exist in strongly scintillated beams make it difficult for conventional adaptive optics systems to remove the phase distortions. When the least-squares reconstructed phase is removed, the vortices still remain. However, we found that the removal of the least-squares phase induces a portion of the vortices to be annihilated during subsequent propagation, causing a reduction in the total number of vortices. This can be understood in terms of the restoration of equilibrium between explicit vortices, which are visible in the phase function, and vortex bound states, which are somehow encoded in the continuous phase fluctuations. Numerical simulations are provided to show that the total number of optical vortices in a strongly scintillated beam can be reduced significantly after a few steps of least-squares phase corrections.

We give a detailed discussion of optimal quantum states for optical two-mode interferometry in the presence of photon losses. We derive analytical formulae for the precision of phase estimation obtainable using quantum states of light with a definite photon number and prove that maximization of the precision is a convex optimization problem. The corresponding optimal precision, i.e., the lowest possible uncertainty, is shown to beat the standard quantum limit thus outperforming classical interferometry. Furthermore, we discuss more general inputs: states with indefinite photon number and states with photons distributed between distinguishable time bins. We prove that neither of these is helpful in improving phase estimation precision.

Multiple electron emission in collisions between bare multiply charged ions and diatomic molecules is studied. The role played by Auger-type emission in cross sections for fixed number of ejected electrons is investigated. It is shown that this postcollisional reaction gives the main contribution to these cross sections at high enough impact velocities. This behavior is accentuated as the ionization degree increases.

A proposal is made to measure the parity-violating energy difference between enantiomers of chiral molecules by modifying the dynamics of the two-state system using an external chiral field, in particular, circularly polarized light. The intrinsic molecular parity-violating energy could be compensated by this external chiral field, with the subsequent change in the optical activity. From the observation of changes in the time-averaged optical activity of a sample with initial chiral purity and minimized environment effects, the value of the intrinsic parity-violating energy could be extracted. A discussion is made on the feasibility of this measurement.

The time-of-flight measurement approach of Peres based on the Salecker-Wigner quantum clock is applied to the one-dimensional scattering of a wave packet from a rectangular barrier. By directly evaluating the expectation value of the clock-time operator in the asymptotic states of wave packet long after the scattering process, we derive an average wave-packet clock time for the barrier interaction, which is expressed as an average of the stationary-state clock time over all possible initial scattering states of the wave packet. We show that the average wave-packet clock time is identical to the average dwell time of a wave packet.

We address the issue of how to properly treat, and in a more general setting, the concept of a weak value of a weak measurement in quantum mechanics. We show that for this purpose, one must take in account the effects of the measuring process on the entire phase space of the measuring system. By using coherent states, we go a step further than Jozsa in a recent paper and we present an example where the result of the measurement is symmetrical in the position and momentum observables and seems to be much better suited for quantum optical implementation.

The multiconfiguration Dirac-Hartree-Fock theory has been employed to calculate the electric dipole moment of the $7s6d{{}^{3}D}_2$ state of radium induced by the nuclear Schiff moment. The results are dominated by valence and core-valence electron correlation effects. We show that the correlation effects can be evaluated in a converged series of multiconfiguration expansions.

The time-dependent multiconfiguration Hartree method is optimized for intense laser dynamics and applied to nonsequential double ionization in a two-electron diatomic model molecule with two dimensions per electron. The efficiency of our method brings these calculations from the realm of large scale computation facilities to single processor machines. The resulting two-electron spectrum exhibits pronounced signatures from which the ionic bound states involved in nonsequential double ionization are retrieved with the help of a semiclassical model. A mechanism for the ionization dynamics is suggested.

The multiphoton dissociation branching ratios for ${{\text{H}}_2}^{+}$ and ${{\text{D}}_2}^{+}$ as a function of laser peak intensity and pulse length are investigated by solving the time-dependent Schrödinger equation in the Born-Oppenheimer approximation, neglecting nuclear rotation. An 800 nm laser pulse with peak intensities from $8\times {10}^9\text{W}/{\text{cm}}^2$ to ${10}^{14}\text{W}/{\text{cm}}^2$ and pulse lengths from 5 to 7.5 fs is used. We also investigate the viability of identifying zero-, one-, two-, and three-photon processes based only on the nuclear kinetic energy release spectrum, and check these identifications with a rigorous Floquet-like method.