We have carried out a comprehensive study of electron impact on open SOS isomer by using the $R$-matrix method. Elastic (integrated and differential), momentum-transfer, excitation, and ionization cross sections along with efffective collision frequency over a wide electron temperature range (100–30 000 K) have been presented. The target states are represented by including correlations via a configuration interaction technique. The results of the static-exchange, correlated one-state, and 31-state close-coupling approximation are presented. Our study has detected a shape resonance, five core-excited shape resonances, and two Feshbach resonances in the 31-state model. We detect a stable bound state of SOS${}^{-}$ having configuration $1a_1^{2}2a_1^2\dots 9a_1^2,1b_1^{2}2b_1^{2}3b_1,1b_2^{2}2b_2^2\dots 7b_2^2,1a_2^{2}2a_2^2$ with a vertical electronic affinity value of 1.999 eV. The ionization cross sections are calculated in the binary-encounter Bethe model in which Hartree-Fock molecular orbitals at self-consistent level are used to calculate kinetic and binding energies of the occupied molecular orbitals.

Absolute total and differential cross sections have been measured for neutral Li formation in single collisions of ${\mathrm{Li}}^{+}$ on ${\mathrm{H}}_2$ from 1 to 5 keV. Total cross sections were obtained by direct integration of measured differential cross sections and are in good agreement with earlier cross-sectional measurements. A comparison of the differential cross sections plotted as a function of the reduced variables $\theta \sin \theta d\sigma /d\Omega$ vs $E\theta$ is also presented with a comparison of the maximum of the curves of the present data. Theoretically, we report state to state and summed charge transfer at collision energies ranging from 0.1 to 25 keV/amu. Cross sections were calculated using a nonadiabatic time-dependent direct approach for study of ion-atom and ion-molecule interaction processes. We verify that the main electron-capture channel is in the $n=2$ state of Li with a large probability for electron capture for impact parameters below 2 a.u. for collisions on both H and ${\mathrm{H}}_2$ in the so-called rotational region of the collision. In the case of atomic hydrogen, the electron-capture probability into the $2s$ and $2p$ states shows an oscillating behavior that smooths out when summed. For the molecular case, we find that for projectile energies larger than 1 keV, ionization effects become important. Our results show good agreement when compared to other available experimental and theoretical data.

We study the scattering of a boson with a fermion with full spatial and temporal resolution based on the one-dimensional Yukawa Hamiltonian. In quantum field theory this interaction is described by the annihilation and creation of bosons with intermediate virtual particle states. We show that this process can be modeled in the center-of-mass frame by a scattering potential, permitting us to interpret the absorption and re-emission processes in quantum mechanical terms of a characteristic force. This Compton force between the fermion and boson is repulsive for large distances and attractive for shorter spacings. We also examine the periodic dynamics of a fermion and a boson that are spatially confined to a ring cavity in which they counterpropagate, enabling us to study interactions independent of the transients that characterize the (one-time) scattering event of two wave packets.

We calculate the effect of interactions on the expansion of ultracold atoms from a single site of an optical lattice. We use these results to predict how interactions influence the interference pattern observed in a time-of-flight experiment. We find that for typical interaction strengths their influence is negligible, yet that they reduce visibility near a scattering resonance.

Three fermions with strongly repulsive interactions in a spherical harmonic trap constitute the simplest nontrivial system that can exhibit the onset of itinerant ferromagnetism. Here, we present exact solutions for three trapped, attractively interacting fermions near a Feshbach resonance. We analyze energy levels on the upper branch of the resonance where the atomic interaction is effectively repulsive. When the $s$-wave scattering length $a$ is sufficiently positive, three fully polarized fermions are energetically stable against a single spin-flip, indicating the possibility of itinerant ferromagnetism, as inferred in the recent experiment. We also investigate the high-temperature thermodynamics of a strongly repulsive or attractive Fermi gas using a quantum virial expansion. The second and third virial coefficients are calculated. The resulting equations of state can be tested in future quantitative experimental measurements at high temperatures and can provide a useful benchmark for quantum Monte Carlo simulations.

In a parameter regime for which the mean-field (Gross-Pitaevskii) dynamics becomes chaotic, mesoscopic quantum superpositions in phase space can occur in a double-well potential, which is shaken periodically. For experimentally realistic initial states, such as the ground state of some 100 atoms, the emergence of mesoscopic quantum superpositions in phase space is investigated numerically. It is shown to be reproducible, even if the initial conditions change slightly. Although the final state is not a perfect superposition of two distinct phase states, the superposition is reached an order of magnitude faster than in the case of the collapse-and-revival phenomenon. Furthermore, a generator of entanglement is identified.

We study possibilities to suppress the transverse modulational instability (MI) of dark-soliton stripes in two-dimensional Bose-Einstein condensates (BEC’s) and self-defocusing bulk optical waveguides by means of quasi-one-dimensional structures. Adding an external repulsive barrier potential (which can be induced in BEC by a laser sheet, or by an embedded plate in optics), we demonstrate that it is possible to reduce the MI wave number band, and even render the dark-soliton stripe completely stable. Using this method, we demonstrate the control of the number of vortex pairs nucleated by each spatial period of the modulational perturbation. By means of the perturbation theory, we predict the number of the nucleated vortices per unit length. The analytical results are corroborated by the numerical computation of eigenmodes of small perturbations, as well as by direct simulations of the underlying Gross-Pitaevskii/nonlinear Schrödinger equation.

We investigated the ground-state wave function and the free expansion of a trapped dipolar condensate. We find that dipolar interaction may induce both biconcave and dumbbell density profiles in the pancake- and cigar-shaped traps, respectively. In the parameter plane of the interaction strengths, the oscillating density profile in a harmonically trapped dipolar condensate occurs only when the interaction parameters fall into certain isolated areas. The relation between the positions of these areas and the trap geometry is explored. When a box potential is used to confine the condensate, spatial density oscillation becomes a generic feature. By studying the free expansion of the condensate with an oscillating density profile, we show that the spatial density oscillation is detectable from the time-of-flight image.

We demonstrate in this paper a method to reconstruct the atom number distribution of a cloud containing a few tens of cold atoms. The atoms are first loaded from a magneto-optical trap into a microscopic optical dipole trap and then released in a resonant light probe where they undergo a Brownian motion and scatter photons. We count the number of photon events detected on an image intensifier. Using the response of our detection system to a single atom as a calibration, we extract the atom number distribution when the trap is loaded with more than one atom. The atom number distribution is found to be compatible with a Poisson distribution.

A theory of autoresonant four-wave mixing in tapered fibers is developed in application to optical parametric amplification (OPA). In autoresonance, the interacting waves (two pump waves, a signal, and an idler) stay phase-locked continuously despite variation of system parameters (spatial tapering). This spatially extended phase-locking allows complete pump depletion in the system and uniform amplification spectrum in a wide frequency band. Different aspects of autoresonant OPA are described including the automatic initial phase-locking, conditions for autoresonant transition, stability, and spatial range of the autoresonant interaction.

We present a mechanism to produce indistinguishable single-photon pulses on demand from an optical cavity. The sequences of two laser pulses generate, at the two Raman transitions of a four-level atom, the same cavity-mode photons without repumping of the atom between photon generations. Photons are emitted from the cavity with near-unit efficiency in well-defined temporal modes of identical shapes controlled by the laser fields. The second-order correlation function reveals the single-photon nature of the proposed source. A realistic setup for the experimental implementation is presented.

We address the properties of optical solitons in thermal nonlinear media with a local refractive index defect that is capable of trapping solitons launched close to the sample boundary despite the boundary-mediated forces that tend to deflect all beams toward the center of the sample. We show that while such forces become more pronounced with an increasing of the input beam power the defect can trap only light below a critical power above which solitons are ejected. The dynamics of soliton ejection and the subsequent propagation may be controlled.

A low-dimensional model is constructed via the proper orthogonal decomposition (POD) to characterize the multipulsing phenomenon in a ring cavity laser mode locked by a saturable absorber. The onset of the multipulsing transition is characterized by an oscillatory state (created by a Hopf bifurcation) that is then itself destabilized to a double-pulse configuration (by a fold bifurcation). A four-mode POD analysis, which uses the principal components, or singular value decomposition modes, of the mode-locked laser, provides a simple analytic framework for a complete characterization of the entire transition process and its associated bifurcations. These findings are in good agreement with the full governing equation.

It is reported experimentally that low-threshold random lasing in a weakly scattering disordered structure formed by speckles using holography is achieved. It shows that the emission property of the structure is related directly to the pulse duration of the pump laser. If pumped by picosecond pulses, several spikes are observed in the emission. If pumped by a nanosecond laser, only a single dominant peak appears. The wavelength tunability of the random laser with a change in temperature has been demonstrated. The corresponding physical analyses have also been provided briefly.

A cavity optoelectromechanical system is reported which combines the ultrasensitive transduction of cavity optomechanical systems with the electrical actuation of nanoelectromechanical systems. Ultrasensitive mechanical transduction is achieved via optomechanical coupling. Electrical gradient forces as large as $0.40$ $\mu$N are realized, facilitating strong actuation with ultralow dissipation. A scanning probe microscope is implemented, capable of characterizing the mechanical modes. The integration of electrical actuation into optomechanical devices is an enabling step toward the regime of quantum nonlinear dynamics and provides capabilities for quantum control of mechanical motion.

We theoretically investigate the high-order harmonic generation (HHG) in helium using a two-color laser field synthesized by an intense 25-fs laser pulse at 800 nm and a relatively weak $~43\text{−}\mathrm{fs}$ laser pulse at 1400 nm. When the polarization between the two pulses is arranged at an angle of $~{73}^{°}$, supercontinuum spectra are dramatically broadened to 180 eV, which is sufficient to support an isolated ∼73-as pulse without any phase compensation. The physical mechanisms behind the phenomenon are well explained in terms of quantum and classical analyses. Furthermore, in the long-pulse regime, this method of extending the supercontinuum spectrum shows the significant advantage over previous two-color HHG schemes.

A systematic correction for Casimir force measurements is proposed and applied to the results of an experiment that was performed more than a decade ago. This correction brings the experimental results into good agreement with the Drude model of the metallic plates’ permittivity. The systematic is due to time-dependent fluctuations in the distance between the plates caused by mechanical vibrations, tilt, or position measurement uncertainty and is similar to the correction for plate roughness.

Although Han et al. [Phys. Rev. Lett. 98, 150404 (2007)] proposed a quantum circuit with six qubits to demonstrate the basic braiding statistics of anyons, we have found that a four-qubit system is enough for realizing such a process. We call it the minimum unit for the fractional statistics of anyons. With some special order, the minimum unit can be used to construct two kinds of fractional charge excitation $n/(n+1)$ [or $(n+1)/n$] and $(n^2-\mathit{kn}+6n+2)/(n^2-\mathit{kn}+5n+4)$ [or $(n^2-\mathit{kn}+2n+k+1)/3(n^2-\mathit{kn}+5n+4)$], where $n,k$ are positive integers and $k⩽n$. This minimum unit can be realized by a photonic quantum simulator or by electrons in an optical lattice or quantum dot array. Its use will have some advantages in metrology.

We operated a high-current wall-stabilized arc to generate a low-temperature, steady-state plasma in nitrogen, with admixtures of argon, helium, and oxygen. We measured the relative atomic transition probabilities for several strong and weak - and - lines of neutral nitrogen and placed them on an absolute scale with experimental lifetime data available in the literature. We obtained good agreement with recent advanced calculations and an earlier measurement for the strong transitions but encountered appreciable discrepancies for weak transitions.

We point out that in higher dimensions, in contrast to the one-dimensional case considered usually, Bloch oscillation driven by a static force can induce transport of the wave packet. The wave packet oscillates constantly, but on a larger time scale it drifts at a constantly velocity permanently. As a noteworthy feature, the net transport in the long run is always normal to the external force and thus controlled by it. We verify this prediction numerically and discuss its experimental realization both with cold atoms in optical lattices and with two-dimensional photonic lattices.