Multiple four-wave-mixing (FWM) processes with multifrequency pumps in optical fibers are investigated theoretically and experimentally. The propagation equations describing the FWM nonlinear interactions between pump waves and “first-order” sideband waves are derived. Based on our theoretical model, the rigorous nonlinear equations governing arbitrary pumps can be developed when the pump waves have equal frequency spacing. The proposed theory can generalize the traditional theory of FWM processes. The rigorous nonlinear equations governing three pumps and three cases of simplified equations governing three, four, and five pumps are achieved. Numerical simulations for three, four, and five pumps are experimentally tested by using a piece of highly nonlinear photonic-crystal fiber, and the experimental observations confirmed our theoretical predictions. The stabilization of waves by multiple FWM processes is proved theoretically and confirmed experimentally.

We present theoretical calculations of the Casimir force for Au thin films near the insulator-conductor transition that has been observed experimentally. The dielectric function of the Au thin films is described by the Drude-Smith model. The parameters needed to model the dielectric function such as the relaxation time, plasma frequency, and the backscattering constant depend on the thickness of the film. The Casimir force decreases as the film thickness decreases until it reaches a minimum after which the force increases again. The minimum of the force coincides with the critical film thickness where a percolation conductor-insulator occurs.

We have studied double Auger decay after $\text{C}1s\to 2{\pi }^{\ast }$ photoexcitation in gas phase carbon monoxide. Two distinct processes, namely direct double Auger decay and cascade double Auger decay, are identified and studied in detail using multiple coincidence techniques. Cascade Auger decay is shown to be the overall dominant process. Decay channels involving the dissociation of the molecule followed by autoionization of the oxygen fragments are observed.

We study the dynamic behavior of ultracold neutral atoms in a macroscopic ac electric trap. Confinement in such a trap is achieved by switching between two saddle-point configurations of the electric field. The gradual formation of a stably trapped cloud is observed and the trap performance is studied versus the switching frequency and the symmetry of the switching cycle. Additionally, the electric field in the trap is mapped out by imaging the atom cloud while the fields are still on. Finally, the phase-space acceptance of the trap is probed by introducing a modified switching cycle. The experimental results are reproduced using full three-dimensional trajectory calculations.

We show that the use of a generalized atom-molecule dark state permits the enhanced coherent creation of triatomic molecules in a repulsive atomic Bose-Einstein condensate, with further enhancement being possible in the case of heteronuclear trimers via the constructive interference between two chemical reaction channels. The creation of fermionic trimers is also briefly discussed.

We calculate the critical power for collapse of linearly polarized phase vortices, and show that this expression is more accurate than previous results. Unlike the nonvortex case, deviations from radial symmetry do not increase the critical power for collapse, but rather lead to disintegration into collapsing non vortex filaments. The cases of circular, radial, and azimuthal polarizations are also considered.

We report on the measurement of the equation of state of a two-component Fermi gas of ${}^6\mathrm{Li}$ atoms with resonant interactions. By analyzing the in situ density distributions of a population-imbalanced Fermi mixture reported in a recent experiment [Y. Shin et al., Nature 451, 689 (2008)], we determine the energy density of a resonantly interacting Fermi gas as a function of the densities of the two components. We present a method to determine the equation of state directly from the shape of the trapped cloud, where the fully polarized, noninteracting ideal Fermi gas in the outer region provides the absolute calibration of particle density. From the density profiles obtained at the lowest temperature, we estimate the zero-temperature equation of state.

We consider a longitudinal expansion of a one-dimensional gas of hard-core bosons suddenly released from a trap. We show that the broken translational invariance in the initial state of the system is encoded in correlations between the bosonic occupation numbers in the momentum space. The correlations are protected by the integrability and exhibit no relaxation during the expansion.

We present a theory of measurement-induced interference for weakly interacting Bose-Einstein-condensed gases. The many-body state resulting from the evolution of an initial fragmented (Fock) state can be approximated as a continuous superposition of Gross-Pitaevskii (GP) states; the measurement breaks the initial phase symmetry, producing a distribution pattern corresponding to only one of the GP solutions. We discuss also analytically solvable models, such as two-mode on-chip adiabatic recombination and soliton generation in quasi-one-dimensional condensates.

We theoretically investigate image storage in hot atomic vapor. A so-called $4f$ system is adopted for imaging and an atomic vapor cell is placed over the transform plane. The Fraunhofer diffraction pattern of an object in the object plane can thus be transformed into atomic Raman coherence according to the idea of “light storage.” We investigate how the stored diffraction pattern evolves under diffusion and discuss the essence of the stability of its dark spots. Our result indicates, under appropriate conditions, that an image can be reconstructed with high fidelity. The main reason for this procedure is the fact that diffusion of opposite-phase components of the diffraction pattern interferes destructively.

We present a theoretical investigation on positron scattering by ${\text{N}}_2\text{O}$. Elastic differential and integral cross sections at both the static and static plus correlation-polarization levels of approximation are calculated and reported in the $0.1–100$ eV. Calculations were performed using two theoretical methods, namely, the Schwinger multichannel method and the method of continued fractions. Also, two different schemes were used to treat correlation-polarization effects. The comparison between our calculated results and the existing experimental data is encouraging.

The mechanism and cross section for dissociative electron attachment of acetylene after collision with electrons in the 0–7 eV range is reported. The positions of the resonances and the autoionization widths are determined by electron scattering calculations using the complex Kohn variational method. The complex potential energy surface relevant to the metastable negative ion ${\text{C}}_2{\text{H}}_2^{-\ast }$ is constructed as a function of the $\text{C}\equiv \text{C}$ and C–H stretches and the CCH angle. The lowest resonant potential is then used as input for the study of the dissociation dynamics within the local complex potential model using the multiconfiguration time-dependent Hartree method. The calculated dissociative electron attachment cross section as a function of electron energy is compared to available experimental findings.

Full-dimensional laser control of HCN-CNH isomerization is carried out to demonstrate the effectiveness of the recently formulated semiclassical guided optimal control theory. The algorithm is designed so that the controlling field does not exceed the predetermined limit of intensity to avoid the undesirable multiphoton inonization process. The controlling field is found to be rather simple and physical understanding of the controlling process becomes possible. It is demonstrated that the quantum-mechanical effects taken into account by the semiclassical treatment are essential for the control and that the purely classical treatment cannot be reliable. The theory is now applicable to any realistic molecular dynamics of many degrees of freedom.

We analyze the outcome of a Mott insulator to superfluid transition for a two-component Bose gas with two atoms per site in an optical lattice in the limit of slow ramping down the lattice potential. This manipulation of the initial Mott-insulating state transforms local correlations between hyperfine states of atom pairs into multiparticle correlations extending over the whole system. We show how to create macroscopic twin Fock states in this way, and that, in general, the obtained superfluid states are highly depleted even for initial ground Mott-insulator states.

The Schrödinger motion of a charged quantum particle in an electromagnetic potential can be simulated by the paraxial dynamics of photons propagating through a spatially inhomogeneous medium. The inhomogeneity induces geometric effects that generate an artificial vector potential to which signal photons are coupled. This phenomenon can be implemented with slow light propagating through a gas of double-$\Lambda$ atoms in an electromagnetically induced transparency setting with spatially varied control fields. It can lead to a reduced dispersion of signal photons and a topological phase shift of Aharonov-Bohm type.

In contrast with filamentation of ultrashort laser pulses with standard Gaussian beams in Kerr media, three different types of Bessel filaments are obtained in air or in water by focusing ultrashort laser pulses with an axicon. We thoroughly investigate the different regimes and show that the beam reshapes as a nonlinear Bessel beam which establishes a conical energy flux from the low intensity tails toward the high intensity peak. This flux efficiently sustains a high contrast long-distance propagation and easily generates a continuous plasma channel in air.

We study the coherence properties of optical vortices stored in atomic ensembles. In the presence of thermal diffusion, the topological nature of stored optical vortices is found not to guarantee slow decoherence. Instead the stored vortex state’s decoherence is surprisingly larger than the stored Gaussian mode. Furthermore, calculation of the coherence factor shows that the center of the stored vortex becomes completely incoherent once diffusion begins and, when a reading laser is applied, the optical intensity at the center of the vortex becomes nonzero. Its implication for quantum information is discussed. A comparison of classical diffusion and quantum diffusion is also presented.

It is generally assumed that the propagation of light through a dielectric medium is always reciprocal under reversal of the propagation direction. We show that in an all-dielectric diffractive system nonreciprocal polarization changes are possible for individual diffracted beams when the diffractive medium possesses two-dimensional chirality. This nonreciprocity is characterized by different eigenstates for the system for the forward and reverse directions respectively, yet it is also entirely consistent with the predictions of the Lorentz reciprocity lemma.

We have determined numerically the maximum quantum violation of over 100 tight bipartite Bell inequalities with two-outcome measurements by each party on systems of up to four-dimensional Hilbert spaces. We have found several cases, including the ones where each party has only four measurement choices, where two-dimensional systems, i.e., qubits, are not sufficient to achieve maximum violation. In a significant proportion of those cases when qubits are sufficient, one or both parties have to make trivial, degenerate “measurements” in order to achieve maximum violation. The quantum state corresponding to the maximum violation in most cases is not the maximally entangled one. We also obtain the result that bipartite quantum correlations can always be reproduced by measurements and states which require only real numbers if there is no restriction on the size of the local Hilbert spaces. Therefore in order to achieve maximum quantum violation on any bipartite Bell inequality (with any number of settings and outcomes), there is no need to consider complex Hilbert spaces.