Spectral line shapes in hot plasmas submitted to a strong oscillating electric field have been theoretically studied by applying the standard hypotheses of plasma line broadening together with a nonperturbative Floquet treatment of the external oscillating field. The formulation has been applied to the lines of nonhydrogenic emitters like He-like and Ne-like ions. It is found that the simultaneous action of a strong oscillating field and plasma particle fields can lead to dramatic changes in the spectral emission.

Some practical improvements are proposed for the “optical-shaker” laser-cooling technique [I. S. Averbukh and Y. Prior, Phys. Rev. Lett. 94, 153002 (2005)]. The improved technique results in an increased cooling rate and decreases the minimum cooling temperature achievable with the optical shaker. The modified shaker requires only one measurement of the force on the atoms before each cooling step, resulting in a simplification of the feedback electronics. The force is inferred from the power variations of the transmitted laser beams and is used to determine the best moment at which the cooling steps are applied. The temperature of the atomic system is automatically monitored, which allows maintaining an optimum cooling rate as the temperature decreases. The improved shaker is simple to build, provides a faster rate of cooling, and can work in the microkelvin regime. Numerical modeling shows a reduction by a factor of 3 in the required number of phase jumps and a lower temperature limit reduced by an order of magnitude compared to the initially proposed shaker. The technique is also extendable to cooling in three dimensions.

We study a model for electron detachment from negative ions by ultrashort unipolar electric pulses. The electron-atom interaction is described by the zero-range potential and the temporal dependence of the electric field is approximated by the Dirac $\delta$ functions. The case of a single pulse can be treated semianalytically and explicit expressions are obtained for momentum and energy distributions of detached electrons as well as for the total detachment probability. The determination of angular distribution involves numerical evaluation of a one-dimensional integral. The case of two alternating electric pulses requires numerical evaluation of more complicated integrals but leads to interesting effects caused by the quantum interference of the electronic wave packets produced during the interactions with the first and the second pulses. The differential and integral detachment probabilities are calculated and discussed for a variety of pulse strengths and time delays between the pulses.

We report on the experimental observation of dynamic localization of a Bose-Einstein condensate in a shaken optical lattice, both for sinusoidal and square-wave forcing. The formulation of this effect in terms of a quasienergy band collapse, backed by the excellent agreement of the observed collapse points with the theoretical predictions, suggests the feasibility of systematic quasienergy band engineering.

We discuss various superfluid properties of a two-component Fermi system in the presence of a tight one-dimensional periodic potential in a three-dimensional system. We use zero temperature mean field theory and derive analytical expressions for the Josephson current, the sound velocity, and the center-of-mass oscillations in the Bardeen, Cooper, and Schrieffer-Bose Einstein condensation (BCS-BEC) crossover region.

We demonstrate that superradiance and collective atomic recoil lasing from cold atoms can be enhanced using a two-frequency pump with frequency difference twice the two-photon recoil frequency ${\omega }_r$. In the good-cavity regime the atoms behave as a three-recoil-level system, collectively scattering a single-frequency radiation mode. In the bad-cavity regime, the superradiant cascade through the different recoil momentum states is strongly accelerated. The emitted radiation shows a discrete spectrum whose harmonics are separated by $2{\omega }_r$ and generated by transitions between adjacent momentum levels.

We work out two different analytical methods for calculating the boundary of the Mott-insulator–superfluid (MI-SF) quantum phase transition for scalar bosons in cubic optical lattices of arbitrary dimension at zero temperature which improve upon the seminal mean-field result. The first one is a variational method, which is inspired by variational perturbation theory, whereas the second one is based on the field-theoretic concept of effective potential. Within both analytical approaches we achieve a considerable improvement of the location of the MI-SF quantum phase transition for the first Mott lobe in excellent agreement with recent numerical results from quantum Monte Carlo simulations in two and three dimensions. Thus, our analytical results for the whole quantum phase diagram can be regarded as being essentially exact for all practical purposes.

Based on standard field-theoretic considerations, we develop an effective action approach for investigating quantum phase transitions in lattice Bose systems at arbitrary temperature. We begin by adding to the Hamiltonian of interest a symmetry breaking source term. Using time-dependent perturbation theory, we then expand the grand-canonical free energy as a double power series in both the tunneling and the source term. From here, an order parameter field is introduced in the standard way and the underlying effective action is derived via a Legendre transformation. Determining the Ginzburg-Landau expansion to first order in the tunneling term, expressions for the Mott insulator-superfluid phase boundary, condensate density, average particle number, and compressibility are derived and analyzed in detail. Additionally, excitation spectra in the ordered phase are found by considering both longitudinal and transverse variations of the order parameter. Finally, these results are applied to the concrete case of the Bose-Hubbard Hamiltonian on a three-dimensional cubic lattice, and compared with the corresponding results from mean-field theory. Although both approaches yield the same Mott insulator–superfluid phase boundary to first order in the tunneling, the predictions of our effective action theory turn out to be superior to the mean-field results deeper into the superfluid phase.

We investigate the formation and coupling of defect modes in two-dimensional photonic crystal (PC) band gaps associated with degenerate edges. Using a method based on Green’s functions and perturbation theory, we derive a condition for the degeneracy of a defect mode in a PC band gap. We show that the interaction between multiple degenerate defects splits this degeneracy and provide a semi-analytic model for the splitting using a $4\times 4$ tight-binding matrix. We observe that the structure of this tight-binding matrix is related to the overlap and corresponding symmetry of the defect modes. We confirm our analysis by comparing with numerical results.

The nonlinear coupled Gross-Pitaevskii equation governing the dynamics of the two-component Bose-Einstein condensate (TBEC) is shown to admit sinusoidal, propagating-wave solutions in quasi-one-dimensional geometry in a trap. The solutions exist for a wide parameter range, which illustrates a procedure for coherent control of these modes through temporal modulation of the parameters, like scattering length and oscillator frequency. The effects of time-dependent coupling and the trap variation on the condensate profile are explained. The TBEC has also been investigated in the presence of an optical lattice potential, where the superfluid phase is found to exist under general conditions.

Using the Madelung transformation we show that in a quantum free-electron laser the beam obeys the equations of a quantum fluid in which the potential is the classical potential plus a quantum potential. The classical limit is shown explicitly.

We study two ions confined in a Penning trap. We show that electronically highly excited states exist in which an electron is delocalized among the two ions forming a giant molecule of several micrometer size. At energies close to the top of the Coulomb barrier, these molecular states can be regarded as superpositions of Rydberg states of individual ions. We illuminate the possibility to observe coherent charge transfer between the ions. Beyond a critical principal quantum number, the electron can coherently tunnel through the Coulomb barrier to an adjacent doubly charged ion. The tunneling occurs on time scales on which the dynamics of the nuclei can be considered frozen and radiative decay can be neglected. The present study can be regarded as a first step toward the implementation of electronic Hubbard models in an ion-trap setup.

We investigate the effect of the anisotropy of a harmonic trap on the behavior of a fast rotating Bose-Einstein condensate. Fast rotation is reached when the rotational velocity is close to the smallest trapping frequency, thereby deconfining the condensate in the corresponding direction. We characterize a regime of velocity and small anisotropy where the behavior is similar to the isotropic case: a triangular Abrikosov lattice of vortices, with an inverted parabola profile. Nevertheless, at sufficiently large velocity, we find that the ground state does not display vortices in the bulk. We show that the coarse-grained atomic density behaves like an inverted parabola with large radius in the deconfined direction and keeps a fixed profile given by a Gaussian in the other direction. The description is made within the lowest-Landau-level set of states, but using distorted complex coordinates.

It is shown how the total internal reflection of orbital-angular-momentum-endowed light can lead to the generation of evanescent light possessing rotational properties in which the intensity distribution is firmly localized in the vicinity of the surface. The characteristics of these surface optical vortices depend on the form of the incident light and on the dielectric mismatch of the two media. The interference of surface optical vortices is shown to give rise to interesting phenomena, including pattern rotation akin to a surface optical Ferris wheel. Applications are envisaged to be in atom lithography, optical surface tweezers, and spanners.

We discuss some aspects related to the so-called Hilbert-space average method, as an alternative to describe the dynamics of open quantum systems. First we present a derivation of the method which does not make use of the algebra satisfied by the operators involved in the dynamics, and extend the method to systems subject to a Hamiltonian that changes with time. Next we examine the performance of the adiabatic quantum search algorithm with a particular model for the environment. We relate our results to the criteria discussed in the literature for the validity of the above-mentioned method for similar environments.

We report on photon emissions in the $200–800\mathrm{nm}$ region resulting from collisions of $200\mathrm{keV}$ protons with ${\mathrm{H}}_2\mathrm{O}$. The most prominent features observed in the spectrum are the Balmer series of hydrogen and two OH molecular bands. Several less intense ${\mathrm{O}}^{+}$ as well as neutral O lines are also observed. The absolute photon emission cross sections of the major lines and bands were measured. The results indicate that a primary dissociation pathway involves the formation of ${\mathrm{H}}_2{\mathrm{O}}^{+}$ by removing a $1b_2$ electron. The unstable ${\mathrm{H}}_2{\mathrm{O}}^{+}$ ion further dissociates into ${\mathrm{H}}^{+}+\mathrm{O}\mathrm{H}$ or $\mathrm{O}{\mathrm{H}}^{+}+\mathrm{H}$. The dominant presence of neutral hydrogen lines and ${\mathrm{O}}^{+}$ lines leads to the conclusion that the subsequent dissociation of $\mathrm{O}{\mathrm{H}}^{+}$ into $\mathrm{H}+{\mathrm{O}}^{+}$ prevails over the other possible dissociation pathway leading to ${\mathrm{H}}^{+}$ and neutral oxygen fragments.

Ionization of the $3p$ orbital of argon by 113.5 and $200\mathrm{eV}$ incident electrons is studied by means of the post version of the CDW-EIS model. Results are presented for 2, 5, and $10\mathrm{eV}$ ejected electrons and compared to recent experimental data from Lohmann and collaborators. The present results are also compared to those obtained by other state-of-the-art theoretical methods. The present system is extremely sensitive to the way in which the post-collision interaction, the electronic exchange and the initial state correlation are considered. We conclude that none of the here discussed methods provides an ultimate description of the system and further theoretical work is needed.

Atomic-vapor density change due to light induced atomic desorption (LIAD) is studied in paraffin-coated rubidium, cesium, sodium, and potassium cells. In the present experiment, low-intensity probe light is used to obtain an absorption spectrum and measure the vapor density, while light from an argon-ion laser, array of light emitting diodes, or discharge lamp is used for desorption. Potassium is found to exhibit significantly weaker LIAD from paraffin compared to Rb and Cs, and we were unable to observe LIAD with sodium. A simple LIAD model is applied to describe the observed vapor-density dynamics, and the role of the cell’s stem is explored through the use of cells with lockable stems. Stabilization of Cs vapor density above its equilibrium value over $25\min$ is demonstrated. The results of this work could be used to assess the use of LIAD for vapor-density control in magnetometers, clocks, and gyroscopes utilizing coated cells.

We derive relations between standard order parameter correlations and the noise correlations in time of flight images, which are valid for systems with long-range order as well as low-dimensional systems with algebraic decay of correlations. Both bosonic and fermionic systems are considered. For one-dimensional Fermi systems we show that the noise correlations are equally sensitive to spin, charge, and pairing correlations and may be used to distinguish between fluctuations in the different channels. This is in contrast to linear response experiments, such as Bragg spectroscopy, which are only sensitive to fluctuations in the particle-hole channel (spin or charge). For bosonic systems we find a sharp peak in the noise correlation at opposite momenta that signals pairing correlations in the depletion cloud. In a condensate with true long-range order, this peak is a $\delta$ function and we can use Bogoliubov theory to study its temperature dependence. Interestingly we find that it is enhanced with temperature in the low-temperature limit. In one-dimensional condensates with only quasi-long-range (i.e., power-law) order the peak in the noise correlations also broadens to a power-law singularity.

We investigate two-component ultracold fermionic atoms with repulsive interactions trapped in an optical lattice with ladder structure. By applying the Bogoliubov–de Gennes equations to an effective $t\text{−}J$ model in the strong correlation limit, we discuss how the spatially modulated spin-singlet pairs with $d$-wave-like symmetry are formed in the systems with trapping potentials. Furthermore, a close examination of the condensation energy as well as the local average of potential, kinetic, and exchange energies by means of the variational Monte Carlo method elucidates that local particle correlations enhance the stability of the superfluid state via a substantial energy gain due to singlet pairing in the high particle density region.