Absolute measurements of cross sections for photoionization of a statistical admixture of ${\mathrm{Ne}}^{+}$ in the ${}^2{P}_{3/2}^o$ ground state and the ${}^2{P}_{1/2}^o$ metastable state are reported in the energy range 40–71 eV at photon energy resolutions ranging from 22 meV to 2 meV. The experiments were performed using synchrotron radiation from an undulator beamline of the Advanced Light Source with a newly developed ion-photon-beam endstation. The data are characterized by multiple Rydberg series of autoionizing resonances superimposed upon a direct photoionization background cross section where some of the observed resonance line shapes show evidence of interference between the direct and indirect photoionization channels. The resonance features are assigned spectroscopically, and their energies and quantum defects are tabulated. The experimental photoionization cross sections are in satisfactory agreement with the predictions from theoretical calculations performed in intermediate coupling using the semirelativistic Breit-Pauli approximation with ten states. The resonances nearest to the ionization thresholds exhibit anomalous behavior with respect to their positions and strengths due to the presence of interloping resonances associated with higher-lying ionic states causing disruption of the regular Rydberg spectral pattern.

A representation of time-dependent Hamiltonians that describe laser-driven systems is presented. Unlike the well-known time-independent dressed potentials that are functions of the characteristic parameter ${\alpha }_0=\sqrt{I}/{\omega }^2,$ where $\omega$ and I are the laser frequency and intensity, this approach provides a time-averaged potential that depends explicitly on the field parameters; e.g., I, $\omega ,$ and shape of the laser pulse. The modified dressed potential is $ħ$ independent and adds a classical time-independent potential barrier to the Kramers-Henneberger dressed potential. We show that this dynamical potential barrier is identical to the Kapitza effective classical potential energy obtained for the motion of a particle in a rapidly oscillating field. As an illustrative numerical example, a simple one-electron effective model Hamiltonian of xenon atom in strong laser field is studied. We show that the zero-order quasienergies obtained by our representation are reasonably accurate and the second order high-frequency perturbation calculations provide quite accurately the lifetime of the photoionized electron for a broad range of laser frequencies.

Optical quantum-nondemolition devices can provide essential tools for quantum information processing. Here, we describe several optical interferometers that signal the presence of a single photon in a particular input state without destroying it. We discuss both entanglement-assisted and nonentanglement-assisted interferometers, with ideal and realistic detectors. We found that the existing detectors with 88% quantum efficiency and single-photon resolution can yield output fidelities of up to 89%, depending on the input state. Furthermore, we construct expanded protocols to perform quantum-nondemolition detections of single photons that leave the polarization invariant. For detectors with 88% efficiency, we found polarization-preserving output fidelities of up to 98.5%.

We present a method of implementation of general projective measurement of the two-photon polarization state with the use of linear optics elements only. The scheme presented succeeds with a probability of at least 1/16. For some specific measurements (e.g., parity measurement) this probability reaches 1/4.

The dynamics of the intrinsic optical bistability (IOB) in an elementary quantum system is investigated in the situation where this system is composed of two weakly interacting subsystems. Numerical calculations have been performed for two “real” systems where IOB has been experimentally observed. The first situation corresponds to the electron-nuclear spin system of $\beta -{\mathrm{Ga}}_2{\mathrm{O}}_3,$ where the transition between electron spin states exhibit a strong bistability. The other situation corresponds to optical transitions in ${\mathrm{Yb}}^{3+}$ pairs in ${\mathrm{CsCdBr}}_3:\mathrm{Yb}$ compound, where IOB has been experimentally observed. It is shown that, in addition to the classical hysteresis of the response of the system upon variation of the power of the external field, the observation of the so-called critical slowing down is a clear signature of IOB.

The $4d$ photoionization and subsequent $N_{4,5}{P}_1{P}_1$ Auger decay in free barium atoms have been investigated with special emphasis on the anomalous intensity ratio in the Auger electron spectrum. In order to understand the details of the spectrum, a series of ab initio calculations based on the multiconfiguration Dirac-Fock method have been performed. Theoretical predictions are compared with high-resolution electron spectra measured using synchrotron radiation. An interference effect, induced through electron correlation, was found to give rise to the anomaly of the intensities.

${\mathrm{H}}_2{\mathrm{O}}_2$ and HOCl were dissociated using circularly polarized light at wavelengths 330–370 nm, and angular-momentum polarization of OH ${(}^2\Pi )$ products was measured using laser induced fluorescence. The OH $\mathrm{}(J=0.5\mathrm{})\mathrm{}$ products exhibit orientation of angular momenta resulting from interference between excited dissociating states of the parent molecules.

We present an experiment for preparing a Werner state via spontaneous parametric down-conversion and controlled decoherence of photons in this paper. In this experiment two independent $\beta$-barium borate crystals are used to produce down-conversion light beams, which are mixed to prepare the Werner state.

The Deutsch-Jozsa algorithm is experimentally demonstrated for three-qubit functions using pure coherent superpositions of ${\mathrm{Li}}_2$ rovibrational eigenstates. The function’s character, either constant or balanced, is evaluated by first imprinting the function, using a phase-shaped femtosecond pulse, on a coherent superposition of the molecular states, and then projecting the superposition onto an ionic final state, using a second femtosecond pulse at a specific time delay.

$K$-shell $\mathrm{}\left(1s\right)\mathrm{}$ and L-shell $\mathrm{}\left(2s\right)\mathrm{}$ ionization potentials for the superheavy elements with $Z=112,$ 114, 116, and 118 are predicted to an accuracy of a few 10 eV using Dirac-Hartree-Fock theory and taking into account quantum electrodynamic and nuclear-size effects. The data obtained are for any number of electrons and can be used in the future in theoretical and experimental studies of these elements involving K-electron conversion spectroscopy.

In this paper we present an experimentally measured value for the linear polarizability of Ag neutral vapor generated by exploding fine wires. The polarizability $\alpha ,$ index of refraction $\eta ,$ and the neutral vapor volume density n are related by the expression $\eta \simeq 1+2\pi n\alpha .$ The neutral vapor density was obtained from x-ray radiographic images taken using an X-pinch backlighter. The index of refraction was measured using an air-wedge shearing interferometer. The polarizability of Ag is obtained from these two measurements and compared to the theoretical predictions. Factors that can affect the measurement accuracy are also discussed.

The triple-differential cross section for electron-impact ionization of a ${\mathrm{Li}}^{+}{(1s}^2)$ ion is considered in the coplanar equal-energy-sharing kinematics at an incident energy of 135.6 eV. The emergence of structures in the calculated cross sections is explained in terms of isolated two-body final-state interactions and three-body coupling. The cross section shows two peaks originating from “classical” sequential two-body collisions. The position of these peaks is determined by two-body final-state interactions. In addition, it is demonstrated that the signature of three-body interactions is carried by the magnitude and ratio of these two peaks. The direct and exchange amplitudes are also considered.

M-subshell x-ray production cross sections are measured for Au, induced by F ions in the energy range of 20 to 102 MeV. For a comparative study the measurements are also carried out for protons, He, Li, C ions at a few energies. We have derived the absolute cross sections for $M\alpha \beta$ and $M\gamma$ x rays as well as the total M x-ray cross sections. The intensity ratios, $I\left(\gamma \right)/I\left(\alpha \beta \right),$ of the $M\left(\gamma \right)$ and $M\left(\alpha \beta \right),$ as well as the energy shifts of these lines signifying multiple vacancies in outer shells have also been studied as a function of projectile atomic number. The measured cross sections are compared with available theoretical calculations, namely, the ECPSSR based on the perturbed stationary state (PSS) approximation including the effects due to the increased binding energy, Coulomb deflection (C), energy loss (E), and relativistic (R) wave function. In case of the $M\gamma$ the measured cross sections are much higher compared to the ECPSSR prediction which is attributed to a dramatic enhancement in the $M_3$-subshell fluorescence yield owing to multiple vacancies in N subshells. The enhancement strongly depends on the projectile atomic number.

Asymmetrical fission of ${\mathrm{C}}_{60}^{r+}$ $(r=4\mathrm{}–9)$ ions are studied in ${\mathrm{Xe}}^{25+}-{\mathrm{C}}_{60}$ collisions at 100 keV impact energy $(v\approx 0.18\mathrm{a}.\mathrm{u}.\mathrm{}).\mathrm{}$ The branching ratios for the emission of a singly or a doubly charged light fragment, ${\mathrm{C}}_m^{+}$ or ${\mathrm{C}}_m^{2+},$ are measured for each initial charge state r. The measured m-dependent branching ratios for the singly charged ${\mathrm{C}}_m^{+}$ fragment emission channels are reproduced using a simple statistical model. The ionization energies $I\left({\mathrm{C}}_{60-2n}^{q+}\right)$ for even numbered fullerenes ${\mathrm{C}}_{60-2n}^{q+}$ $(q=1\mathrm{}–5,8;n=1\mathrm{}–4)$ and $I\left({\mathrm{C}}_{2n}^{+}\right)$ for singly charged light fragments ${\mathrm{C}}_{2n}^{+}$ $(n=1\mathrm{}–4)$ are estimated by the density-functional theory. The total branching ratio for the ${\mathrm{C}}_m^{2+}$ emission channels is found to increase from less than 2 to 25% when the charge r of the parent ion ${\mathrm{C}}_{60}^{r+}$ increases from 5 to 9.

We study the quantum dynamics of the center-of-mass momentum distribution for the populations of a cold gas with two-level system undergoing spontaneous decay and coupled to a Markovian thermal reservoir at arbitrary temperature. We derive the momentum-convolutionless coupled equations for momentum Fourier transform of the populations which can be easily solved numerically and analytically for a specific internal scheme and for zero-temperature cases. The time and momentum evolutions of the populations are obtained by inverse Fourier transform. The momentum spread and the center-of-mass entropy across one momentum dimension are computed and compared for different internal schemes, between zero-temperature and finite-temperature cases and between $\pi$ and ${\sigma }_{\pm }$ transitions. For initial subrecoil momentum width, the ${\sigma }_{\pm }$ transition displays a two-peak feature. Our results well describe the momentum spread dynamics of cold gas in thermal radiation at early time and complement the results based on Fokker-Planck equation.

The parametric resonant behavior of ions inside a linear rf ion trap is studied both theoretically and experimentally. Theoretically, the resonant motion of ions inside an ideal ion trap is described by approximating the trapping rf field as a harmonic pseudopotential with the ions being excited by an additional quadrupolar ac voltage. The resulting damped Mathieu equation is studied and the regions of resonant instability are predicted by investigating the solutions. Experimentally, the parametric excitation of ${\mathrm{Mg}}^{+}$ ions is observed by subjecting the cloud of trapped ions to an additional quadrupolar ac field. The various ion motion resonances are detected through the disappearance of the laser-induced fluorescence signal. Weak damping is introduced by the presence of a low-pressure buffer gas. The experimental results are compared with the theoretical predictions.

The final stage of Bose-Einstein condensation (BEC) in a large volume occurs through coarsening—growth of individual correlated patches. We present analytical arguments and numerical evidence that in the momentum space, this growth corresponds to strong turbulence of the particle number, with a turbulent cascade towards the infrared and the power law $n\left(k\right)\mathrm{}\propto k^{-\mathrm{}(d+1\mathrm{})\mathrm{}}$ in $d=2,3\mathrm{}$ spatial dimensions. As a corollary, we find that the correlation length grows linearly in time, with the speed of order of the speed of Bogoliubov’s quasiparticles (phonons). We use these results to estimate the speed of BEC in atomic vapors and in galactic dark matter.

We present a representative set of analytic stationary-state solutions of the nonlinear Schrödinger equation for a symmetric double-square-well potential for both attractive and repulsive nonlinearity. In addition to the usual symmetry-preserving even and odd states, nonlinearity introduces quite exotic symmetry-breaking solutions—among them are trains of solitons with different number and sizes of density lumps in the two wells. We use the symmetry-breaking localized solutions to form macroscopic quantum superposition states and explore a simple model for the exponentially small tunneling splitting.

We propose a configuration that utilizes electromagnetically induced transparency (EIT) to tailor a fiber mode propagating inside a thin optical fiber and coherently control its dispersion properties to drastically reduce the group velocity of the fiber mode. The key to this proposal is that the evanescent field of the thin fiber strongly couples with the surrounding active medium, so that the EIT condition is met by the medium. We show how the properties of the fiber mode are modified due to the EIT medium, both numerically and analytically. We demonstrate that the group velocity of the modified fiber mode can be drastically reduced $(\approx 44\mathrm{}\mathrm{m}/\mathrm{s}\mathrm{e}\mathrm{c})$ using the coherently prepared orthohydrogen doped in a matrix of parahydrogen crystal as the EIT medium.

Fluorescence lifetimes of thin, rhodamine 6G-doped polymer layers in front of a mirror have been determined as a function of the emitter-mirror separation and the conditions of excitation and observation. Lifetime is well known to depend on the spatial emitter-mirror separation. The explanation of experimental data needs to consider direction, polarization, and numerical aperture of the experimental system. As predicted theoretically, experimental results depend on the conditions of illumination and observation, because of the different lifetimes of emitters aligned horizontally or vertically with respect to the plane of interfaces and their selection by the experimental system. This effect is not observable when ions are used as a source of fluorescence, because ensemble averaging depends on the properties of sources.