Lifetimes of four short-lived levels belonging to the ${4f}^8{(}^{7}F)6p$ configuration of Tb III have been measured using a two-step excitation time-resolved laser-induced fluorescence technique. They agree quite well with multiconfigurational relativistic Hartree-Fock calculations performed with inclusion of core-polarization effects. Using the experimental lifetimes and the theoretical branching fractions, a set of transition probabilities has been deduced for this ion.

We show that while high-energy photoionization cross sections converge to their asymptotic forms only at relativistic energies, the leading deviation from the asymptotic energy dependence of nonrelativistic photoionization cross sections at high energy is the same for all cross sections. This factor can be obtained explicitly, and only asymptotic forms are needed for the remainder at high nonrelativistic energies. Since the factor is common, ratios of photoionization cross sections reach their asymptotic values at much lower energies than the cross sections themselves. Results are presented both in independent-particle approximation as well as including correlation effects, which modify the asymptotic behavior, especially for light elements or outer shells.

A theoretical model for electron excitation of atoms accompanying inner-shell ionization is presented here. Both the sudden creation of an inner-shell vacancy and the Coulomb interaction between the ionized electron and atomic electrons are taken into consideration. The transition amplitude is expressed as the sum of the conventional shake process and multipole transitions through the direct Coulomb interaction between electrons. The L-shell excitation probabilities accompanying K-shell photoionization of Ne are calculated and the contributions from the Coulomb interaction are discussed.

The $L\alpha ,$ $L_{\beta },$ and $L\gamma$ x-ray production cross sections of In, Sn, and Re by electron impact were measured at energies from near threshold to tens of keV. Thin targets with thick substrates were used in the experiments. We compare the experimental results of Sn x-ray production cross sections with data determined by Baxter and Spicer [Aust. J. Phys. 36, 287 (1983)] with a different method, and present some results. The measured x-ray production cross sections are also compared with the binary encounter approximation theory of Gryzinski [Phys. Rev. 138, A336 (1965)] and the atomic-rearrangement theory of McGuire [Phys. Rev. A 16, 73 (1977)]. It is found that the L-shell production cross sections do not exhibit a gradual increase with atomic number, a result observed by Park et al. [Phys. Rev. A 12, 1358 (1975)] in a systematic study of L-shell x-ray production cross sections by MeV electron impact. For the present measured L-shell data of In and Sn, it seems that, so far, none of the available theories can adequately interpret the L-shell results at low energies.

We show that entanglement is a useful resource to enhance the mutual information of the depolarizing channel when the noise on consecutive uses of the channel has some partial correlations. We obtain a threshold in the degree of memory above which a higher amount of classical information is transmitted with entangled signals.

The quantum-mechanical state vector is not directly observable even though it is the fundamental variable that appears in Schrödinger’s equation. In conventional time-dependent perturbation theory, the state vector must be calculated before the experimentally observable expectation values of relevant operators can be computed. We discuss an alternative form of time-dependent perturbation theory in which the observable expectation values are calculated directly and expressed in the form of nested commutators. This result is consistent with the fact that the commutation relations determine the properties of a quantum system, while the commutators often have a form that simplifies the calculation and avoids canceling terms. The usefulness of this method is illustrated using several problems of interest in quantum optics and quantum information processing.

The semiclassical quantization rule is derived for a system with a spherically symmetric potential $V\left(r\right)\mathrm{}\sim r^{\nu }(-2<\mathrm{}\nu <\infty )$ and an Aharonov-Bohm magnetic flux. Numerical results are presented and compared with known results for models with $\nu =-1,0,2,\infty .$ It is shown that the results provided by our method are in good agreement with previous results. One expects that the semiclassical quantization rule shown in this paper will provide a good approximation for all principle quantum numbers, including the large principle quantum number $n\gg 1.$ The rule is even derived in the large principal quantum number limit $n\gg 1.$ We also discuss the power parameter $\nu$ dependence of the energy spectra pattern in this paper.

A concept of polarization entanglement for continuous variables is introduced. For this purpose the Stokes-parameter operators and the associated Poincaré sphere, which describe the quantum-optical polarization properties of light, are defined and their basic properties are reviewed. The general features of the Stokes operators are illustrated by evaluation of their means and variances for a range of simple polarization states. Some of the examples show polarization squeezing, in which the variances of one or more Stokes parameters are smaller than the coherent-state value. The main object of the paper is the application of these concepts to bright squeezed light. It is shown that a light beam formed by interference of two orthogonally polarized quadrature-squeezed beams exhibits squeezing in some of the Stokes parameters. Passage of such a primary polarization-squeezed beam through suitable optical components generates a pair of polarization-entangled light beams with the nature of a two-mode squeezed state. Implementation of these schemes using the double-fiber Sagnac interferometer provides an efficient method for the generation of bright nonclassical polarization states. The important advantage of these nonclassical polarization states for quantum communication is the possibility of experimentally determining all of the relevant conjugate variables of both squeezed and entangled fields using only linear optical elements followed by direct detection.

It is pointed out that the possibility of teleporting an arbitrary unknown one-particle spin state is crucially connected with the maximal entanglement of the Einstein-Podolsky-Rosen pair, whose one-particle reduced density matrix is $\rho \mathrm{}\left(i\right)=\frac{1}{2}{\mathbf{I}}_2$ $\mathrm{}(i=1,2\mathrm{}).$ It is shown that, to teleport an arbitrary k-particle spin state, one must prepare an ancillary N-particle $(N>~2k)$ entangled state, whose k-particle reduced density matrix has the form ${(1/2\mathrm{}}^k){\mathbf{I}}_{2^k}$ $({\mathbf{I}}_{2^k}$ is the $2^k\times 2^k$ identity matrix). An alternative approach to constructing many-particle entangled states is developed by using $R_x\left(\pi \right),$ the collective rotation of $\pi$ around a given axis (say, x axis). The entangled states constructed by using $R_x\left(\pi \right)$ operating on the basis of angular momentum uncoupling representation are just the GHZ states, which cannot be used for the teleportation of an arbitrary k $(>~2)$ particle spin state. The entangled states constructed by using $R_x\left(\pi \right)$ operating on the basis of angular momentum coupling representation turn out to be effective for the teleportation of an arbitrary multiparticle state. A formal extension of the scheme of Bennett et al. to deal with the teleportation of an arbitrary two (or more) particle spin state is discussed.

A mechanism of strong-field continuum-interference stabilization of atoms is proposed. Stabilization is assumed to arise owing to interference of different-order continuum-continuum and bound-continuum transitions. In the framework of perturbation theory the threshold of stabilization is estimated qualitatively, and the estimates are shown to be in a reasonably good agreement with existing experimental data and the results of numerical simulations. The considered mechanism clarifies the physics of adiabatic stabilization at ${\alpha }_0{/a}_{\mathrm{at}}<1.\mathrm{}$

In this paper, we consider the dynamics of a system coupled to a thermal bath, going beyond the standard two-level system through the addition of an energy excitation degree of freedom. Further extensions are to systems containing many fermions, with the master equations modified to take Fermi-Dirac statistics into account, and to potentials with a time-dependent bias that induce resonant avoided crossing transitions. The limit $\overrightarrow{Q}\infty ,$ where the interaction rate with the bath is much greater than all free oscillation rates for the system, is investigated. Two behaviors are possible: freezing (quantum Zeno effect) or synchronization (motional narrowing). We clarify the conditions that give rise to each possibility, making an explicit connection with quantum-measurement theory. We compare the evolution of quantal coherence for the two cases as a function of Q, noting that full coherence is restored as $\overrightarrow{Q}\infty .$ Using an extended master equation, the effect of system-bath interactions on entanglement in bipartite system states is computed. In particular, we show that the sychronization case sees bipartite system entanglement fully preserved in the large Q limit.

Local minimum solutions to Heisenberg’s uncertainty principle are studied in detail. Of particular concern is obtaining an optimal procedure to squeeze the uncertainty in one canonical operator while introducing, in a well-defined mathematical sense, the least possible increase in the uncertainty of the relevant conjugate operator. The result is a hierarchy of “minimum uncertainty $(\mu -)$ wavelets,” which are intimately associated with the “Hermite distributed approximating functionals” [D. K. Hoffman and D. J. Kouri, Phys. Rev. Lett. 85, 5263 (2000)]. The $\mu$ wavelets can be used with any quantum state to squeeze the uncertainty of a particular observable. Several specific examples are given and some possible applications are discussed.

Making use of the physical properties of core electrons the Hamiltonian of the system can be simplified. To study electronic processes involving core electrons, e.g., their ionization, one can work with a reduced effective Hamiltonian operating in valence space only. It accounts for the response of the valence electrons to the presence of a core hole. Because of the two possible spin quantum numbers of the remaining core electron, the effective Hamiltonian has $2\times 2$ matrix form which complicates the evaluation of the ionization spectrum. An elegant transformation is introduced to diagonalize the operator matrix giving rise to a scalar effective Hamiltonian. With its help an exact linked cluster theorem for the core Green’s function, which is directly related to the spectrum, is derived. The resulting cluster function is analyzed in some detail.

In Coster-Kronig electrons from the autoionizng Rydberg states of 64 MeV ${\mathrm{S}}^{12+}$ ions excited through He gas and very thin C-foil targets, several peaks have been observed in the electron energy range up to 2.5 eV. To obtain a better understanding on low-energy electron production mechanisms in such collisions, we synthesize the expected electron spectrum by assuming that the spectral (energy) distribution of each line can be expressed with a Gaussian profile with proper resolution and compare that with the observed spectrum. Two theoretical methods, namely, the perturbation theory of the Z-expansion (MZ code) and multiconfiguration Hartree-Fock method (Cowan code) are used to calculate Auger electron energies and rates. It is found that the $1s2p15l–1s2s{}^{1}S,\hspace{0.5em}1s2p13l–1s2s{}^{3}S,\hspace{0.5em}{1s}^{2}2p9l–{1s}^{2}2s,\hspace{0.5em}{1s}^{2}2s2p9l–{1s}^2{2s}^2,\hspace{0.5em}{1s}^2{2p}^{2}7l–{1s}^{2}2s2p{}^{3}P,$ and ${1s}^2{2p}^{2}9l–{1s}^{2}2s2p{}^{1}P$ decays give a significant contribution in the electron spectrum near threshold in the range of 0–2.5 eV. Synthetic spectra have been found to reproduce the observed spectra reasonably well if the ion charge distributions are taken into account properly. Based upon the synthetic electron spectra from particular core configurations best fitted to the observed spectra, we have inferred the ion charge “inside” foils which can be compared with the well-established equilibrium charge “after” foil.

The moving-mirror problem is microscopically formulated without invoking the external boundary conditions. The moving mirrors are described by the quantized matter field interacting with the photon field, forming dynamical cavity polaritons: photons in the cavity are dressed by electrons in the moving mirrors. The effective Hamiltonian for the polariton is derived, and corrections to the results based on the external boundary conditions are discussed.

We study quantum and classical dynamics of the electron in ionization stabilization of the two-dimensional hydrogen atom irradiated by an intense circularly polarized laser. When the quantum time evolution of the wave packet is stable but the corresponding classical time evolution is diffusive, stabilization can be understood to arise from the effect of quantum localization that suppresses classically chaotic diffusion. When both the quantum and classical time evolutions exhibit a stable behavior, stabilization can be regarded as originating from stable classical orbits generated by nonlinear resonance. We also investigate the effect of the bare Coulomb singularity on ionization stabilization.

It is proven that any hidden variable theory of the type proposed by Meyer [Phys. Rev. Lett. 83, 3751 (1999)], Kent [ibid. 83, 3755 (1999)], and Clifton and Kent [Proc. R. Soc. London, Ser. A 456, 2101 (2000)] leads to experimentally testable predictions that are in contradiction with those of quantum mechanics. Therefore, it is argued that the existence of dense Kochen-Specker-colorable sets must not be interpreted as a nullification of the physical impact of the Kochen-Specker theorem once the finite precision of real measurements is taken into account.

We construct the pseudopotential for two particles subjected to an isotropic harmonic trapping potential while interacting through a hard-sphere potential, and demonstrate that this trap pseudopotential reduces to the standard “zero range” interaction when the ratio of the hard-sphere diameter and the oscillator length is small. We also show that the standard approximation, even when applied to tight traps, is surprisingly accurate.

The existence of well-defined quasiprobabilities has long been known to be the signature of a classical state. Recent studies on environment induced decoherence have suggested the use of the Wigner function to illustrate the destruction of coherence on interaction with the environment. Due to the overcompleteness of coherent states, any state can be represented as a mixture of coherent states with a relative weight $P\left(v\right).$ This is known as the P representation of the state. In this paper we use the P representation of a state to see how its classical form emerges on interaction with the environment. We also use the concept of “depth of classicality” introduced recently to see how classicality is increased on interaction with the environment. We use the example of superposition of Gaussian wave packets for all the calculations. We also attempt to implement the predictability sieve using the P representation of a state. We use this definition of the predictability sieve to show that coherent states are more robust to environment-induced decoherence than squeezed states.

Large-photon-number path entanglement is an important resource for enhanced precision measurements and quantum imaging. We present a general constructive protocol to create any large-photon-number path-entangled state based on the conditional detection of single photons. The influence of imperfect detectors is considered and an asymptotic scaling law is derived.