Electron impact vibrational excitation of the CO molecule, via the ${}^2\Pi$ resonance, in the $0–4\mathrm{eV}$ energy region has been investigated. The energy dependence of the resonant excitation of the first ten vibrational levels, $v=1$ to $v=10$, has been measured by use of a crossed-beams double trochoidal electron spectrometer. Obtained relative differential cross sections are normalized to the absolute values. Integral cross sections are determined by using our recent results on scattered electrons angular distributions, which demonstrate clear $p$-partial wave character of this resonance. Substructures appear in the ${}^2\Pi$ resonant excitation of the CO molecule which have not been previously observed.

We report the performance of a laser-driven polarized internal hydrogen gas target (LDT) in a configuration similar to that used in scattering experiments. This target used the technique of spin-exchange optical pumping to produce nuclear spin polarized hydrogen gas that was fed into a cylindrical storage (target) cell. We present in this paper the performance of the target, methods that were tried to improve the figure-of-merit (FOM) of the target, and a Monte Carlo simulation of spin-exchange optical pumping. The dimensions of the apparatus were optimized using the simulation and the experimental results were in good agreement with the results from the simulation. The best experimental result achieved was at a hydrogen flow rate of $1.1\times {10}^{18}\text{atoms}∕\mathrm{s}$, where the sample beam exiting the storage cell had 58.2% degree of dissociation and 50.5% polarization. Based on this measurement, the atomic fraction in the storage cell was 49.6% and the density averaged nuclear polarization was 25.0%. This represents the highest FOM for hydrogen from an LDT and is higher than the best FOM reported by atomic beam sources that used storage cells.

The endohedral fullerene structures of medium-sized ${\mathrm{Si}}_{\mathrm{N}}$ $(30⩽\mathrm{N}⩽39)$ clusters have been studied using the density functional theory (DFT) with gradient correction. For each cluster size, fullerene cages with different topologies and those filled by a different number of atoms were constructed. These cage isomers were then optimized by DFT-based molecular dynamic relaxations followed by numerical optimization. Compared with recent theoretical calculations [S. Yoo, J. J. Zhao, J. L. Wang, and X. C. Zeng, J. Am. Chem. Soc. 126, 13845 (2004)], the energies of the lowest-energy fullerene cage structures obtained here are lower for most clusters. In particular, the optimal filling and/or cage combination ratios for ${\mathrm{Si}}_{37}$ and ${\mathrm{Si}}_{38}$ were found to be ${\mathrm{Si}}_5@{\mathrm{Si}}_{32}$ and ${\mathrm{Si}}_6@{\mathrm{Si}}_{32}$, different from the previously proposed ones (${\mathrm{Si}}_3@{\mathrm{Si}}_{34}$ and ${\mathrm{Si}}_4@{\mathrm{Si}}_{34}$).

We investigate the ground state of the system of $N$ bosons enclosed in a hard-wall trap interacting via a repulsive or attractive $\delta$-function potential. Based on the Bethe ansatz method, the explicit ground state wave function is derived and the corresponding Bethe ansatz equations are solved numerically for the full physical regime from the Tonks limit to the strongly attractive limit. It is shown that the solution takes a different form in different regime. We also evaluate the one body density matrix and second-order correlation function of the ground state for finite systems. In the Tonks limit the density profiles display the Fermi-like behavior, while in the strongly attractive limit the Bosons form a bound state of $N$ atoms corresponding to the $N$-string solution. The density profiles show the continuous crossover behavior in the entire regime. Further, the correlation function indicates that the Bose atoms bunch closer as the interaction constant decreases.

The fluorescence light emitted by a four-level system in $J=1∕2$ to $J=1∕2$ configuration driven by a monochromatic laser field and in an external magnetic field is studied. We show that the spectrum of resonance fluorescence emitted on the $\pi$ transitions shows a signature of spontaneously generated interference effects. The degree of interference in the fluorescence spectrum can be controlled by means of the external magnetic field, provided that the Landé $g$ factors of the excited and the ground state doublet are different. For a suitably chosen magnetic field strength, the relative weight of the Rayleigh line can be completely suppressed, even for low intensities of the coherent driving field. The incoherent fluorescence spectrum emitted on the $\pi$ transitions exhibits a very narrow peak whose width and weight depend on the magnetic field strength. We demonstrate that the spectrum of resonance fluorescence emitted on the $\sigma$ transitions shows an indirect signature of interference. A measurement of the relative peak heights in the spectrum from the $\sigma$ transitions allows us to determine the branching ratio of the spontaneous decay of each excited state into the $\sigma$ channel.

We present a double-pass optical loop containing a purely dispersive and an essentially purely nonlinear element as a potential fast intensity oscillator. The residual dispersion in the nonlinear element is found to play a key role in the dynamics. We analytically investigate the dynamics of the loop both for normal and anomalous dispersion, using linear and weakly nonlinear analysis. Numerically, stable operation is found for normal residual dispersion, while a tendency to multimode and irregular spiking is observed for anomalous dispersion. The effect of losses is also discussed.

A time-dependent approach for calculation of the triple differential cross section of sequential double photoionization of atoms by femto- and attosecond pulses is developed. The method involves the numerical solving of a system of coupled nonstationary Schrödinger equations which describe the inner-shell photoionization and the following Auger decay. The shape of the spectra and the angular distributions of photoelectrons are considered in the near-threshold region for the case of photoelectron–Auger electron coincidence experiments as well as for noncoincidence measurements. As examples, the cross sections for $\mathrm{Ar}\left(2p\right)$ and $\mathrm{Kr}\left(3d\right)$ sequential double photoionization are calculated and discussed. It is shown that the cross sections strongly depend on the duration of the ionizing pulse. In contrast, the asymmetry parameters, characterizing the angular distribution of photoelectrons, are practically independent of the characteristics of the pulse.

We give a detailed derivation of the master-equation description of the coherent backscattering of laser light by cold atoms. In particular, our formalism accounts for the nonperturbative nonlinear response of the atoms when the injected intensity saturates the atomic transition. Explicit expressions are given for total and elastic backscattering intensities in the different polarization channels, for the simplest nontrivial multiple-scattering scenario of intense laser light multiply scattering from two randomly placed atoms.

We establish a quantitative relationship between the entanglement content of a single quantum chain at a critical point and the corresponding entropy of entanglement. We find that, surprisingly, the leading critical scaling of the single-copy entanglement with respect to any bipartitioning is exactly one-half of the entropy of entanglement, in a general setting of conformal field theory and quasifree systems. Conformal symmetry imposes that the single-copy entanglement scales as $E_1\left({\rho }_L\right)=(c∕6)\ln L-(c∕6)({\pi }^2∕\ln L)+O(1∕L)$, where $L$ is the number of constituents in a block of an infinite chain and $c$ denotes the central charge. This shows that from a single specimen of a critical chain, already half the entanglement can be distilled compared to the rate that is asymptotically available. The result is substantiated by a quantitative analysis for all translationally invariant quantum spin chains corresponding to all isotropic quasifree fermionic models. An example of the $XY$ spin chain shows that away from criticality the above relation is maintained only near the quantum phase transition.

We study a model of an equal mixture of two species of fermions in a deep optical lattice at a filling of two fermions per site. At weak interspecies interaction, the system is a band insulator. When the interspecies interaction is tuned via a Feshbach resonance to be larger than an energy related to the energy separation of the first and second Bloch bands, atoms populate equally the two Bloch bands. With weak tunneling between sites of the optical lattice, the system becomes a Mott insulator with the low-energy effective Hamiltonian of a spin-1 Heisenberg antiferromagnet, because of a Hund’s-rule-like coupling between the two bands. We discuss experimental signatures of these two types of insulators.

We investigate the properties of single vortices and of the vortex lattice in a rotating dipolar condensate. We show that vortices in this system possess several features induced by the long-range anisotropic dipolar interaction between particles. For example, when the dipoles are polarized along the rotation axis, vortices may display a craterlike structure; when dipoles are polarized orthogonal to the rotation axis, the vortex cores take an elliptical shape and the vortex lattice no longer possesses hexagonal symmetry.

We characterize the photon-counting statistics of single-chromophore systems submitted to continuous laser radiation and embedded in a complex structured environment able to induce strong non-Markovian effects in the decay dynamics. In the weak-laser-excitation regime, the photon-emission process can be described through a delay function. We demonstrate that the dynamics, by itself, is able to develop a non-Poissonian intermittent fluorescence phenomenon where the bright and dark intervals are characterized by probability distributions that may depart from an exponential one.

We discuss the problem of implementing generalized measurements [positive operator-valued measures (POVMs)] with linear optics, either based upon a static linear array or including conditional dynamics. In our approach, a given POVM shall be identified as a solution to an optimization problem for a chosen cost function. We formulate a general principle: the implementation is only possible if a linear-optics circuit exists for which the quantum mechanical optimum (minimum) is still attainable after dephasing the corresponding quantum states. The general principle enables us, for instance, to derive a set of necessary conditions for the linear-optics implementation of the POVM that realizes the quantum mechanically optimal unambiguous discrimination of two pure nonorthogonal states. This extends our previous results on projection measurements and the exact discrimination of orthogonal states.

We investigate the effect of a spin bath on the spin-transfer functions of a permanently coupled spin system. When each spin is coupled to a separate environment, the effect on the transfer functions in the first excitation sector is amazingly simple: the group velocity is slowed down by a factor of 2, and the fidelity is destabilized by a modulation of $\mid \cos Gt\mid ,$ where $G$ is the mean square coupling to the environment.

We study the optimal way to estimate the quantum expectation value of a physical observable when a finite number of copies of a quantum pure state are presented. The optimal estimation is determined by minimizing the squared error averaged over all pure states distributed in a unitary invariant way. We find that the optimal estimation is “biased” though the optimal measurement is given by successive projective measurements of the observable. The optimal estimate is not the sample average of observed data, but the arithmetic average of observed and “default nonobserved” data, with the latter consisting of all eigenvalues of the observable.

A study of inner-shell electron-impact ionization of heavy neutral atoms is presented. A relativistic distorted-wave method is used to calculate $K$-shell ionization of neutral Mn, Fe, Ni, and Cu, and also the $L$-shell ionization of neutral W. These calculations are compared with measurements made by electron-impact ionization from a thin target of the atomic species in question. Good agreement is found between the calculations and measurements.

A four electrode electrostatic trap geometry is demonstrated that can be used to combine a dipole, quadrupole, and hexapole field. A cold packet of ${}^{15}\mathrm{ND}_3$ molecules is confined in both a purely quadrupolar and hexapolar trapping field and additionally, a dipole field is added to a hexapole field to create either a double-well or a donut-shaped trapping field. The profile of the ${}^{15}\mathrm{ND}_3$ packet in each of these four trapping potentials is measured, and the dependence of the well-separation and barrier height of the double-well and donut potential on the hexapole and dipole term are discussed.

A theory of gravitational quantum states of ultracold neutrons in waveguides with absorbing/scattering walls is presented. The theory covers recent experiments in which the ultracold neutrons were beamed between a mirror and a rough scatterer/absorber. The analysis is based on a recently developed theory of quantum transport along random rough walls which is modified in order to include leaky (absorbing) interfaces and, more importantly, the low-amplitude high-aperture roughness. The calculations are focused on a regime where the direct transitions into the continuous spectrum above the absorption threshold dominate the depletion of neutrons from the gravitational states and are more efficient than the processes involving the intermediate states. The theoretical results for the neutron count are sensitive to the correlation radius (lateral size) of surface inhomogeneities and to the ratio of the particle energy to the absorption threshold in the weak-roughness limit. The main impediment for observation of the higher gravitational states is the “overhang” of the particle wave functions which can be overcome only by using scatterers with strong roughness. In general, strong roughness with high amplitude is preferable if one wants just to detect the individual gravitational states, while strong-roughness experiments with small amplitude and high aperture are preferable for the quantitative analysis of the data. We also discuss ways to further improve the accuracy of calculations and to optimize the experimental regime.

The best three-channel projectile-inelastic close-coupling approximation (CCA) is used to study the resonances in positronium (Ps) and hydrogen (H) scattering at the energy region below the inelastic threshold. The $s$-wave elastic phase shifts and $s$-wave elastic cross sections are studied using the static-exchange, two- and three-channel projectile-inelastic CCA for both the singlet (+) and triplet $(-)$ channels. The singlet resonances detected using different CCA schemes confirm previous predictions [Drachman and Houston, Phys. Rev. A 12, 885 (1975); Page, J. Phys. B. 9, 1111 (1976)]. We report a resonance in the triplet channel too using the present three-channel CCA scheme.

Malley discussed [Phys. Rev. A 69, 022118 (2004)] that all quantum observables in a hidden-variable model for quantum events must commute simultaneously. In this comment, we discuss that Malley’s theorem is indeed valid for the hidden-variable theoretical assumptions, which were introduced by Kochen and Specker. However, we give an example that the local hidden-variable (LHV) model for quantum events preserves noncommutativity of quantum observables. It turns out that Malley’s theorem is not related to the LHV model for quantum events, in general.