The results of experimental and theoretical studies on elastic-electron scattering by indium atom are presented. The measurements are performed at incident electron energies of $E_0=10$, 20, 40, 60, 80, and 100 eV within the scattering angles ranging from $10°$ to $150°$. Theoretical calculations have been carried out using both complex and real optical potentials and cover the energy range up to $E_0=350\text{eV}$. We report on relative differential cross sections (DCSs), integral $\left({\sigma }_{\text{el}}\right)$, momentum-transfer $\left({\sigma }_m\right)$, and viscosity $\left({\sigma }_v\right)$ cross sections for elastic-electron scattering. The energy dependence of the angular positions of DCS minima is also determined. Two data sets were calculated, with and withoutt an absorption potential being compared to the experimental results.

We present the biorthogonal complement of the standing wave state and its relation to scattering operators. This establishes a completeness relation in terms of the standing wave states, and therefore completes the $\mathit{R}$-matrix (reactance matrix) theory of scattering. We clarify with an example that the $\mathit{R}$-matrix theory, in its formulation presented here, can claim its due place in addition to the standard $\mathit{T}$-matrix theory.

We report the enhancement of dielectronic recombination from a continuum of finite bandwidth in combined electric and magnetic fields. Specifically, we have examined the process Ba $6p_{3/2}8g\to 6p_{1/2}ng\to 6s_{1/2}ng+h\nu$ for $32\le n\le 47$ in combined fields ranging from 0 to 7 V/cm and 0 to 250 G. The results demonstrate that it is the component of $B\perp E$ that leads to enhancement. The experimental results indicate that the $\mathit{B}$ field coupling must exceed the radiative rate, the autoionization rate, and the Stark splitting of the intermediate autoionizing Rydberg states.

We theoretically study the optical properties of a gas of ultracold, coherently dressed three-level atoms in a Mott insulator phase of an optical lattice. The vacuum state, the band dispersion and the absorption spectrum of the polariton field can be controlled in real time by varying the amplitude and the frequency of the dressing beam. In the weak dressing regime, the system shows unique ultraslow-light propagation properties without absorption. In the presence of a fast time modulation of the dressing amplitude, we predict a significant emission of photon pairs by parametric amplification of the polaritonic zero-point fluctuations. Quantitative considerations on the experimental observability of such a dynamical Casimir effect are presented for the most promising atomic species and level schemes.

We obtain the equations of motion for a ferromagnetic Bose condensate of arbitrary spin in the long-wavelength limit. We find that the magnetization of the condensate is described by a nontrivial modification of the Landau-Lifshitz equation, in which the magnetization is advected by the superfluid velocity. This hydrodynamic description, valid when the condensate wave function varies on scales much longer than either the density or spin healing lengths, is physically more transparent than the corresponding time-dependent Gross-Pitaevskii equation. We discuss the conservation laws of the theory and its application to the analysis of the stability of magnetic helices and Larmor precession. Precessional instabilities, in particular, provide a novel physical signature of dipolar forces.

We propose a technique for distinguishing the origin of a four-wave mixing (FWM) signal. This technique is based on nonlinear Fourier-transform spectroscopy (FTS) combined with the use of a broadband pulse. We theoretically analyze FWM-FTS and show that the response function in FWM is obtained from the FWM power spectrum calculated by the Fourier transform of an interferometric autocorrelation signal. When a broadband pulse is employed as an excitation light source, the FWM power spectrum shows not only Raman resonance but also two-photon electronic resonance. By comparing the FWM power spectrum of a resonant sample with that of a nonresonant reference sample, the origin of FWM is identified. By employing theoretical analysis, we experimentally demonstrate FWM-FTS using a 5-fs broadband pulse. By combining the use of a 5-fs pulse with nonlinear FTS based on two-photon excited fluorescence, we also successfully measured a two-photon excitation spectrum with a bandwidth of 300 nm.

Semilocal density functionals such as the local-spin-density and generalized-gradient approximations are known to overestimate the polarizabilities and especially the hyperpolarizabilities of long-chain molecules, the latter by as much as a factor of 10 or more in model hydrogen chains. These quantities are much better predicted by exact-exchange methods such as Hartree-Fock or optimized effective potential. We show here that the semilocal functionals, after full or scaled-down Perdew-Zunger self-interaction correction (SIC), are about as good as the exact-exchange methods for these quantities. As is the case for the exact-exchange methods, SIC is fully nonlocal and exact for all one-electron densities, and (more relevantly to the electrical response) tends to maintain an integer number of electrons on each ${\mathrm{H}}_2$ chain unit to a greater extent than the semilocal functionals do. In this study, the SIC energy is minimized directly, without an optimized effective potential.

For a system composed of two particles, Bell’s theorem asserts that averages of physical quantities determined from local variables must conform to a family of inequalities. In this work we show that a classical model containing a local probabilistic interaction in the measurement process can lead to a violation of the Bell inequalities. We first introduce two-particle phase-space distributions in classical mechanics constructed to be the analogs of quantum-mechanical angular momentum eigenstates. These distributions are then employed in four schemes characterized by different types of detectors measuring the angular momenta. When the model includes an interaction between the detector and the measured particle leading to ensemble dependencies, the relevant Bell inequalities are violated if the total angular momentum is required to be conserved. The violation is explained by identifying assumptions made in the derivation of Bell’s theorem that are not fulfilled by the model, in particular noncommutativity of single-particle measurements. We discuss to what extent a violation of these assumptions is a faithful marker of nonlocality.

The role of the description of initial and final states in $\left(\gamma ,2e\right)$ and high incident energy $\left(e,3e\right)$ collisions with helium targets is investigated. We describe the double continuum as a product of plane waves modulated by three Coulomb distortion factors and propose different sets of initial states which satisfy exactly all two-body Kato cusp conditions. Wave functions with only angular correlation, and with both angular and radial correlation, are considered; in each case, the interparticle correlation factors are such that they have different (polynomial, exponentially increasing or decreasing, and oscillatory) asymptotic behaviors. The gauge discrepancies observed in $\left(\gamma ,2e\right)$ calculations show that the overall agreement with absolute $\left(e,3e\right)$ experimental data at $10+10\text{eV}$ ejected energy obtained with simple initial states is fortuitous and can hardly be attributed to a balanced description with respect to the final state. Thus the description of the final state by the product of plane waves and three Coulomb distortion factors is not suitable to describe sufficiently well the double continuum of two electrons ejected at 10 eV. An investigation of the ejected energy dependence on both double ionization processes further illustrates that what is observed at $10+10\text{eV}$ ejected energy does not necessarily hold at higher values. Further theoretical studies and new experimental data are clearly needed to help understand the interplay of initial and final states.

We consider ultracold atoms in a far detuned optical lattice across a high-$Q$ optical resonator. Applying an external driving laser to the atoms red detuned from the cavity mode by one vibrational quantum induces cavity-enhanced sideband cooling. For a dense and cold enough atomic ensemble we predict an oscillation threshold for optical Raman sideband lasing concurrent with coherent matter-wave amplification. Above threshold, photons and atoms in the lowest band are dominantly created pairwise via stimulated emission with a strong suppression of competing spontaneous processes. In close analogy to a nondegenerate parametric oscillator, we find sub-Poissonian photon statistics and almost perfect nonclassical atom-photon number correlations. Injecting atoms in higher vibrational bands via tunneling or incoherent scattering then leads to continuous, simultaneous generation of a coherent atom beam and laser light with nonclassical atom-field correlations.

We study three (nested, parallel, and sequential cascade) types of schemes for doubly dressed four-wave-mixing processes in an open five-level atomic system. The interaction between two dressing fields of the nested-cascade scheme is strongest and weakest for the parallel-cascade scheme, with the sequential scheme intermediate between them. Mutual-dressing processes and constructive or destructive interference between two coexisting dressed multiwave mixing channels in such a system are also considered. Investigations of these multidressing mechanisms and interactions are very useful to understand and control the generated high-order nonlinear optical signals.

A set of mode-coupled excitation equations for the slowly growing amplitudes of dielectric waveguide eigenmodes is derived as a description of the electromagnetic signal field of a high-gain free-electron laser (FEL), including the effects of longitudinal space charge. This approach of describing the field basis set has notable advantages for FEL analysis in providing an efficient characterization of eigenmodes, and in allowing a clear connection to free-space propagation of the input (seeding) and output radiation. The formulation describes the entire evolution of the radiation wave through the linear gain regime, prior to the onset of saturation, with arbitrary initial conditions. By virtue of the flexibility in the expansion basis, this technique can be used to find the direct coupling and amplification of a particular mode. A simple transformation converts the derived coupled differential excitation equations into a set of coupled algebraic equations and yields a matrix determinant equation for the FEL eigenmodes. A quadratic index medium is used as a model dielectric waveguide to obtain an expression for the predicted spot size of the dominant system eigenmode, in the approximation that it is a single Gaussian mode.

A high-gain free-electron laser is modeled using an expansion of the radiation field in terms of guided Laguerre-Gaussian modes of a virtual dielectric waveguide [E. Hemsing, A. Gover, and J. Rosenzweig, preceding paper, Phys Rev. A 77, 063830 (2008)]. The radiation profile evolution, power gain, and detuning efficiency characteristics are investigated for seeding with fundamental Gaussian and higher-order Laguerre-Gaussian input modes on a Gaussian $\mathit{e}$-beam in the collective regime. The full wave evolution solution at different seed radiation injection conditions results in determination of the optimal waist size and waist position of the seed radiation beam for maximum power coupling efficiency. Results for guided mode evolution and power gain are shown to be consistent with simulations performed with the code GENESIS 1.3. The amplification and spontaneous generation of FEL radiation with orbital angular momentum is also considered.

Adiabatic quantum algorithms are often most easily formulated using many-body interactions. However, experimentally available interactions are generally two-body. In 2004, Kempe, Kitaev, and Regev introduced perturbative gadgets, by which arbitrary three-body effective interactions can be obtained using Hamiltonians consisting only of two-body interactions. These three-body effective interactions arise from the third order in perturbation theory. Since their introduction, perturbative gadgets have become a standard tool in the theory of quantum computation. Here we construct generalized gadgets so that one can directly obtain arbitrary $\mathit{k}$-body effective interactions from two-body Hamiltonians. These effective interactions arise from the $\mathit{k}$th order in perturbation theory.

The evolution of entanglement in a one-dimensional Ising chain is numerically studied under various initial conditions. We analyze two problems concerning the dynamics of entanglement: (i) generation of the entanglement from the pseudopure separable state and (ii) transportation of the entanglement from one end of the chain to the other. The model investigated is a one-dimensional Ising spin-1/2 chain with nearest-neighbor interactions placed in an external magnetic field and irradiated by a weak resonant transverse field. The possibility of selective initialization of partially entangled states is considered. It was shown that, in spite of the use of a model with direct interactions between the nearest neighbors, entanglement between remote spins is generated.

One-parameter family of discrete-time quantum-walk models on the square lattice, which includes the Grover-walk model as a special case, is analytically studied. Convergence in the long-time limit $t\to \infty$ of all joint moments of two components of walker’s pseudovelocity, $X_t/t$ and $Y_t/t$, is proved and the probability density of limit distribution is derived. Dependence of the two-dimensional limit density function on the parameter of quantum coin and initial four-component qudit of quantum walker is determined. Symmetry of limit distribution on a plane and localization around the origin are completely controlled. Comparison with numerical results of direct computer simulations is also shown.

By extending the concept of interaction-free imaging to the few-atom level, we show that asymptotically on-demand interaction- and measurement-free quantum logic gates can be realized for both single-atom and single-photon qubits. The interaction-free feature suppresses the possibility of qubit decoherence via atomic spontaneous decay, while the elimination of measurements can significantly reduce errors arising from detector inefficiency. We present a general theory of universal quantum Zeno gates, and discuss physical implementations for quantum-information processing with individual atoms and photons. In addition, we propose a loss-tolerant protocol for long-distance quantum communication using quantum Zeno gates incorporated into a Mach-Zehnder interferometer. The efficiency of our Zeno gates is limited primarily by the imprecise control of atom-photon scattering and the finite number of feedback cycles $N$ due to the limited finesse of the optical ring cavity. We find that the success probability scales as $1-O\left(1/N\right)$, and for realistic parameters could be as high as 98.4%. Successful generation of atom-atom entanglement can be heralded by detection of the ancillary photon, upon which the fidelity scales as $1-O\left(1/N^2\right)$, with an achievable fidelity of 99.994%, which comes at the cost of reducing the success probability by the detector efficiency.

Whereas single- and two-photon wave packets are usually treated as pure states, in practice they will be mixed. We study how entanglement created with mixed photon wave packets is degraded. We find in particular that the entanglement of a delocalized single-photon state of the electromagnetic field is determined simply by its purity. We also discuss entanglement for two-photon mixed states, as well as the influence of a vacuum component.

Results from a joint experimental and theoretical investigation of electron-impact excitation of the $\left(5d^{10}6s\right){{}^{2}S}_{1/2}\to \left(5d^{10}6p\right){{}^{2}P}_{1/2,3/2}$ resonance transitions in gold atoms are presented. The calculations were performed using three fully relativistic approaches, namely, a distorted-wave ansatz, a convergent close-coupling method, and a $B$-spline $R$-matrix method. The experimental data are independently normalized to the Bethe-Born formula using the currently preferred experimental values of the optical oscillator strengths. There is generally good agreement between the measured and predicted energy dependences of the integral cross section, provided that sufficient care is taken in the theoretical structure models to ensure that the proper optical oscillator strengths for the two transitions are obtained. A strong resonance feature seen only in the near-threshold excitation of the $\left(5d^{10}6p\right){{}^{2}P}_{1/2}$ state is classified as a $\left(5d^{10}6p^2\right){{}^{1}D}_2$ temporary state of the negative gold ion.

Analytic expressions are obtained for relativistic electron momentum and angular distributions in the tunneling and barrier-suppression ionization of multicharged atomic ions by a superintense linearly polarized field. The Landau-Dykhne approach is used for derivation of these distributions. The condition for applicability of this adiabatic approximation requires that an ejected electron should have sufficiently high kinetic energy so that the ionization probability should be exponentially small. The electron momentum can be both less and larger than the relativistic quiver momentum. In the vicinity of the quiver momentum we found a new peculiarity: sharp cusp in the momenum distribution along the polarization of laser radiation. It is absent at the nonrelativistic ionization of atomic ions by moderate laser fields. The electron momentum spectra along the laser electric field and along the laser magnetic field do not depend on the sign of momentum. In contrast, the relativistic momentum spectra along the direction of propagation of laser radiation and along in the opposite sense are significantly different.