We address a fundamental issue in quantum mechanics and quantum information theory—the generation of an entangled pair of qubits that interact solely through a third, semiclassical degree of freedom—in the framework of cavity quantum electrodynamics. We show that finite, although not maximal, entanglement is obtainable in the classical limit, at the price of a diverging effective interaction time. The optimal atomic entanglement derives from a trade-off between the atomic entanglement in a sub-wave packet and the purity of the atomic state. Decoherence by photon loss sets an upper limit on the degree of excitation of the cavity mode, beyond which the achievable entanglement decreases as the inverse mean photon number to the sixth power.

The applicability of entanglement percolation protocol to real Internet structure is investigated. If the current Internet can be used directly in the quantum regime, the protocol can provide a way to establish long-distance entanglement when the links are pure nonmaximally entangled states. This applicability is primarily due to the combination of scale-free degree distribution and a high level of clustering, both of which are widely observed in many natural and artificial networks including the current Internet. It suggests that the topology of real Internet may play an important role in entanglement establishment.

The third-order expression for the dispersion interaction between two atoms is written as a sum over lists of transition matrix elements. Particular attention is given to the $C_9/R^9$ interaction which occurs in the homonuclear case when one atom is in an $S$ state and the other is in a $P$ state. Numerical values of the $C_9$ coefficient are given for the homonuclear alkali-metal dimers. The size of the $C_9$:$C_3$ dispersion coefficient ratio increases for the heavier alkali-metal atoms. The $C_{11}$ and $C_{13}$ coefficients between two helium atoms and lithium atoms in their ground states are also given.

In this paper, we investigate small clusters of helium atoms using the hyperspherical harmonic basis. We consider systems with $A=2,3,4,5,6$ atoms with an interparticle potential which does not present a strong repulsion at short distances. We use an attractive Gaussian potential that reproduces the values of the dimer binding energy, the atom-atom scattering length, and the effective range obtained with one of the widely used He-He interactions, the Aziz and Slaman potential, called LM2M2. In systems with more than two atoms, we consider a repulsive three-body force that, by construction, reproduces the trimer binding energy of the LM2M2 potential. With this model, consisting of the sum of a two- and three-body potential, we have calculated the spectrum of clusters formed by four, five, and six helium atoms. We have found that these systems present two bound states, one deep and one shallow, close to the threshold fixed by the energy of the $(A-1)$-atom system. Universal relations between the energies of the excited state of the $A$-atom system and the ground-state energy of the $(A-1)$-atom system are extracted, as well as the ratio between the ground state of the $A$-atom system and the ground-state energy of the trimer.

We study the prospects of controlling transmission of broadband and bichromatic laser pulses through turbid samples. The ability to focus transmitted broadband light is limited via both the scattering properties of the medium and the technical characteristics of the experimental setup. There are two time scales given by pulse stretching in the near- and far-field regions which define the maximum bandwidth of a pulse amenable to focusing. In the geometric-optics regime of wave propagation in the medium, a single setup can be optimal for focusing light at frequencies $\omega$ and $n\omega$ simultaneously, providing the basis for the $1+n$ coherent quantum control. Beyond the regime of geometric optics, we discuss a simple solution for the shaping, which provides the figure of merit for one’s ability to simultaneously focus several transmission modes.

Ellipsoidal dielectric particles may be trapped in a linearly polarized Gaussian beam such that they are harmonically bound with respect to each of their rotational and translational degrees of freedom. The ellipsoid belongs to the highest symmetry class for which this is possible. Typically, the longest axis of the ellipsoid aligns itself with the incident beam axis and the second longest with the polarization direction. We investigate this special property by evaluating the trap stiffness matrix for dielectric ellipsoids with aspect ratios (largest:smallest dimension) in the range 1–10, using the discrete dipole approximation. The results are interpreted using a simple phenomenological model and conclusions are drawn concerning optimization of the trap stiffness for specific applications.

It is shown, both through simulations and experiments, that the in-line holographic microscopy technique can be used to retrieve very small refractive-index perturbations caused during the filamentation of ultrashort laser pulses. This technique provides the possibility of having spatially and temporally (four dimensions) resolved measurements of refractive-index changes, down to 10${}^{-4}$, from objects with diameters as small as 10 μm. Moreover, we demonstrate the power of the technique in discriminating multiple filaments in a precise quantitative way.

In all existing mode-locked lasers, the ultimate limit on the output pulse duration is set by the bandwidth of the gain medium. Yet the technique of coherent mode locking allows one to generate broadband pulses from a laser with a linearly narrowband active medium by exploiting the coherent properties of the amplifier. In this work we numerically demonstrate how to use this technique for the generation of single-cycle pulses directly from a mode-locked oscillator.

The generation of entanglement between two identical coupled cavities, each containing a single three-level atom, is studied when the cavities exchange two coherent photons and are in the $N=2,4$ manifolds, where $N$ represents the maximum number of photons possible in either cavity. The atom-photon state of each cavity is described by a qutrit for $N=2$ and a five-dimensional qudit for $N=4$. However, the conservation of the total value of $N$ for the interacting two-cavity system limits the total number of states to only 4 states for $N=2$ and 8 states for $N=4$, rather than the usual 9 for two qutrits and 25 for two five-dimensional qudits. In the $N=2$ manifold, two-qutrit states dynamically generate four maximally entangled Bell states from initially unentangled states. In the $N=4$ manifold, two-qudit states dynamically generate maximally entangled states involving three or four states. The generation of these maximally entangled states occurs rather rapidly for large hopping strengths. The cavities function as a storage of periodically generated maximally entangled states.

Experimental and theoretical study of the $3d$ photoionization and subsequent Auger decay of initially neutral atomic germanium is presented. The features of the high-resolution photoelectron and Auger electron spectra are interpreted with the aid of multiconfiguration calculations. The binding energies and relative cross sections of the $3d$ ionized fine-structure states of Ge are given. The complete $M_{4,5}NN$ Auger electron spectrum to doubly ionized final states of the Ge ion is interpreted and discussed.

Recent developments in the theoretical treatment of electronic energy losses of bare and screened ions in gases are presented. Specifically, the unitary-convolution-approximation (UCA) stopping-power model has proven its strengths for the determination of nonequilibrium effects for light as well as heavy projectiles at intermediate to high projectile velocities. The focus of this contribution will be on the UCA and its extension to specific projectile energies far below 100 keV/u, by considering electron-capture contributions at charge-equilibrium conditions.

The fragmentation of isolated water molecules on collision with 450-keV Ar${}^{9+}$ has been studied using time-of-flight mass spectrometry employing multihit detection. The kinetic energy release spectrum for the dissociation of ${\left[{\text{H}}_2\text{O}\right]}^{2+☆}$ into (${\text{H}}^{☆},{\text{H}}^{+},{\text{O}}^{+}$) fragments has been measured where H${}^{☆}$ is a neutral Rydberg hydrogen atom. Ab initio calculations are carried out for the lowest states of ${\left[{\text{H}}_2\text{O}\right]}^{q+}$ with $q=2$ and 3 to help interpret the kinetic energy release spectra.

We investigate high-order harmonic generation (HHG) from asymmetric molecules exposed to intense laser fields. We show that the emissions of odd and even harmonics depend differently on the orientation angle, the internuclear distance, as well as the effective charge. This difference mainly comes from different roles of intramolecular interference in the HHG of odd and even harmonics. These roles map the structure of the asymmetric molecule to the odd vs even HHG spectra.

The fully variational Hartree-Fock-Bogoliubov approach for bosons is studied in the limit of zero-range forces in two and three dimensions. The equation of state obtained in two dimensions is expressed in a parametric form. It is shown that the $\Lambda$ potential permits to perform an implicit summation of the ladder diagrams without leaving the variational scheme, restoring thus the consistency of this approximation.

We propose photon-statistics excitation spectroscopy as an adequate tool to describe the optical response of a nonlinear system. To this end we suggest to use optical excitation with varying photon statistics as another spectroscopic degree of freedom to gather information about the system in question. The responses of several simple model systems to excitation beams with different photon statistics are discussed. Possible spectroscopic applications in terms of identifying lasing operation are pointed out.

This paper reports computational results of the total cross sections for electron impact on H${}_2$CO and HCOOH over a wide range of electron impact energies from 0.01 eV to 2 keV. The total cross section is presented as sum of the elastic and electronic excitation cross sections for incident energies. The calculation uses two different methodologies, below the ionization threshold of the target the cross section is calculated using the UK molecular $R$-matrix code through the Quantemol-N software package while cross sections at higher energies are evaluated using the spherical complex optical potential formalism. The two methods are found to be consistent at the transition energy (∼15 eV). The present results are, in general, found to be in good agreement with previous experimental and theoretical results (wherever available) and, thus, the present results can serve as a benchmark for the cross section over a wide range of energy.

The structures and magnetic properties of Pd${}_n$ and Pd${}_{n-1}$Mn clusters ($n$ = 3–19) are investigated by using a spin-polarized density functional theory approach. Several different lowest-energy structures of Pd${}_n$ clusters ($n$ = 11, 12, 14, 17) are found. It is shown that when a Mn atom is doped into the Pd${}_n$ cluster, the cluster structure does not change for $n$ < 9, while Mn doping gives rise to a geometry reconstruction for $n$ > 9. The doping of a Mn atom enhances the stability of Pd${}_n$ clusters and increases their magnetic moment by a magnitude of (3–5)μ${}_{\mathrm{B}}$. Moreover, we observe an evident oscillation of steplike magnetic behavior in Pd${}_n$ clusters upon doping of a Mn atom, and the origin of such a magnetic phenomenon is analyzed in detail.

The cross sections for the formation of the metastable atomic hydrogen in the 2$s$ state in photoexcitation of H${}_2$ and D${}_2$ were measured as a function of the incident photon energy in the range of the doubly excited states with their symmetries of the electronic states, ${}^1{\Sigma }_u^{+}$ or ${}^1{\Pi }_u$, being resolved. It has turned out from the comparison with the cross-section curves for other dissociation processes and the theoretical calculation [J. D. Bozek et al., J. Phys. B 39, 4871 (2006)] that the $Q_2$${}^1{\Pi }_u$(1) doubly excited state of H${}_2$ dissociates into both H(2$s$) + H(2$p$) and H(2$p$) + H(2$p$). The dissociation dynamics of this state has been discussed in terms of the nonadiabatic transition during neutral dissociations.

We show that in contrast with contact interacting gases, an optical lattice changes drastically the stability properties of a dipolar condensate, inducing a crossover from dipolar destabilization to dipolar stabilization for increasing lattice depths. Performing stability measurements on a ${}^{52}$Cr Bose-Einstein condensate in an interaction-dominated regime, repulsive dipolar interaction balances negative scattering lengths down to $-17$ Bohr radii. Our findings are in excellent agreement with mean-field calculations, revealing the important destabilizing role played by intersite dipolar interactions in deep lattices.