A general algebraic procedure for constructing coherent states of a wide class of exactly solvable potentials, e.g., Morse and Pöschl-Teller, is given. The method, a priori, is potential independent and connects with earlier developed ones, including the oscillator-based approaches for coherent states and their generalizations. This approach can be straightforwardly extended to construct more general coherent states for the quantum-mechanical potential problems, such as the nonlinear coherent states for the oscillators. The time evolution properties of some of these coherent states show revival and fractional revival, as manifested in the autocorrelation functions, as well as, in the quantum carpet structures.

We present an experimental analysis of quadrature entanglement produced from a pair of amplitude squeezed beams. The correlation matrix of the state is characterized within a set of reasonable assumptions, and the strength of the entanglement is gauged using measures of the degree of inseparability and the degree of Einstein-Podolsky-Rosen (EPR) paradox. We introduce controlled decoherence in the form of optical loss to the entangled state, and demonstrate qualitative differences in the response of the degrees of inseparability and EPR paradox to this loss. The entanglement is represented on a photon number diagram that provides an intuitive and physically relevant description of the state. We calculate efficacy contours for several quantum information protocols on this diagram, and use them to predict the effectiveness of our entanglement in those protocols.

Projectile-induced plasmon excitation in an electron gas has been studied by several authors who proposed two possible mechanisms for these plasmons to decay. In a previous work we considered one of these mechanisms in which the plasmon transfers its energy to a nearly free electron that makes an interband transition. In this paper, the other mechanism is analyzed. A simple model is developed to describe plasmon decay in aluminum via the excitation of two interacting electrons. Results for the transition probability and the excitation power are presented. When contributions from both mechanisms are considered, they account for more than 60% of the excited plasmons. Also, the slope of the plasmon excitation curve is correctly reproduced. The study of first and second differential spectra in angle and energy show that plasmon decay into two interacting electrons is the main source of low-energy electrons moving in the forward direction (with respect to the projectile initial velocity).

The emission of x rays by clusters of moderate to large size ${(10\mathrm{}}^4–{10}^6$ constituents) irradiated by an intense laser pulse ${(10\mathrm{}}^{16}–{10}^{19}{\mathrm{W}/\mathrm{c}\mathrm{m}}^2)$ is considered. Over-the-barrier ionization of the constituent cluster atoms generates multicharged ions and electrons. For increasing cluster size, more and more of the electrons remain trapped inside the cluster. X rays are generated in the interaction of the trapped electrons with the cluster ions. Three such radiative processes are considered in detail: direct photorecombination of free electrons and ions, dielectronic recombination, and excitation of ions by electron impact followed by recombination. The main contribution to x-ray emission under the above conditions comes from electron impact excitation, while dielectronic recombination is less important, and photorecombination hardly plays any role. The excitation is created before the cluster explodes, whereas emission of x rays continues thereafter.

Critical behavior of solitonic wave forms of Bose-Einstein condensates in optical lattices (OL’s) has been studied in the framework of the continuous mean-field equation. In two and three-dimensions OL’s bright matter-wave solitons undergo abrupt delocalization as the strength of the OL is decreased below some critical value. A similar delocalizing transition happens when the coefficient of nonlinearity crosses the critical value. As opposed, bright solitons in one-dimensional OL’s retain their integrity over the whole range of parameter variations. An interpretation of this phenomenon in terms of quantum bound states in the effective potential is proposed.

We use the auxiliary field method to obtain a quantized Hamilton formalism for charged particles interacting with absorptive dielectrics. We give various equivalent representations. For absorptive dielectrics extending over all space, such as absorptive photonic crystals, our formalism is equivalent to that of Dung et al. [Phys. Rev. A 65, 043813 (2002)]. We also show that, as for nonabsorptive photonic crystals, to leading order the excited states of embedded two-level atoms do not decay radiatively if their transition frequencies are in a band gap.

Soliton propagation is usually described in the “slowly varying envelope approximation” regime, which is not applicable for ultrashort pulses. We present theoretical results and numerical simulations for both nonlinear Schrödinger and parametric $\left({\chi }^{\mathrm{}\left(2\right)\mathrm{}}\right)$ ultrashort solitons in the “generalized few-cycle envelope approximation” regime, demonstrating their altered propagation.

We propose a quantum algorithm for simulation of the Anderson transition in disordered lattices and study numerically its sensitivity to static imperfections in a quantum computer. In the vicinity of the critical point the algorithm gives a quadratic speedup in computation of diffusion rate and localization length, comparing to the known classical algorithms. We show that the Anderson transition can be detected on quantum computers with 7–10 qubits.

We implement the Bernstein-Vazirani algorithm on a 15-bit register encoding $2^{15}$ elements using optics. The algorithm provides a polynomial speed up for oracle queries. The apparatus is physically efficient in that its size (i.e., space-time volume) scales linearly with the size (i.e., number of digits) of the register. We demonstrate also that the algorithm may be performed not only without entanglement, but also with a computational basis that does not consist of orthogonal states, and that this coding is the source of the efficiency of the algorithm.

We derive a set of criteria to decide whether a given projection measurement can be, in principle, exactly implemented solely by means of linear optics. The derivation can be adapted to various detection methods, including photon counting and homodyne detection. These criteria enable one to obtain no-go theorems easily for the exact distinguishability of orthogonal quantum states with linear optics, including the use of auxiliary photons and conditional dynamics.

This paper discusses ways to implement two-qubit gate operations for quantum computing with cold trapped ions within one step. The proposed scheme is widely robust against parameter fluctuations and its simplicity might help to increase the number of qubits in present experiments. The basic idea is to use the quantum Zeno effect originating from continuous measurements on a common vibrational mode to realize gate operations with very high fidelities. The gate success rate can, in principle, be arbitrarily high but operation times comparable to other schemes can only be obtained by accepting success rates below 80%.

A procedure based on a variational principle is developed for determining the local Kohn-Sham (KS) potential corresponding to a given ground-state electron density. This procedure is applied to calculate the exchange-correlation part of the effective Kohn-Sham (KS) potential for the neon atom and the methane molecule.

Interference structures associated with the emission of electrons from ${\mathrm{H}}_2$ by fast ${\mathrm{Kr}}^{33+}$ ions $(v/c=0.3)$ are found to exhibit oscillations of second order superimposed on the main oscillatory structure. The secondary oscillations occur with about twice the frequency of the main oscillations. While the primary structure is produced by the coherent emission of electrons from the two atomic centers, similar to Young’s two-slit experiment, our theoretical analysis indicates that the frequency doubling is a second-order effect, where the electron wave emitted at one center interferes with the wave backscattered at the other center.

Effects of the open-shell electronic structure of atomic Sn on the $4d$ photoelectron and Auger electron spectra have been studied by both theory and experiment. The $5p$ and $4d$ photoelectron spectra and the ${4d}^{-1}\to {5p}^{-2}$ Auger spectrum have been measured from atomic tin using synchrotron radiation for excitation. Relativistic Dirac-Fock calculations have been carried out for the energies and intensities of photoelectron and Auger electron transitions from each thermally populated initial state level. It has been shown by a comparison of the experimental and theoretical spectra that the weakly populated excited neutral states, negligible in the direct photoionization process, play an important role in the formation of the Auger spectrum of the open-shell atoms.

In this paper, we report on a scheme to generate a pulsed polarization entangled photon pair through the use of a Sagnac interferometer. To demonstrate its workability, we experimentally obtained two-photon quantum interference for the polarization variable. The main advantage of this scheme is its exceptional stability, compared to other schemes based on the interferometric technique. It does not need any active or passive techniques to stabilize the interferometer, even the instrument is exposed to a relatively turbulent environment.

We consider quantum circuits made of controlled-NOT (CNOT) gates and single-qubit unitary gates and look for constructions that minimize the use of CNOT gates. We show, by means of an explicit quantum circuit, that three CNOT gates are necessary and sufficient in order to implement an arbitrary unitary transformation of two qubits. We also identify the subset of two-qubit gates that can be performed with only two CNOT gates and provide a simple characterization for them.

We classify multipartite entangled states in the Hilbert space $\mathcal{H}=C^2\otimes C^2\otimes C^n(n>~4),$ for example, the four-qubit system distributed over three parties, under local filtering operations. We show that there exist nine essentially different classes of states, giving rise to a five-graded partially ordered structure, including the celebrated Greenberger-Horne-Zeilinger and W classes of three qubits. In particular, all $2\times 2\times n$ states can be deterministically prepared from one maximally entangled state, and some applications such as entanglement swapping are discussed.

We consider optimal cloning of the spin coherent states in Hilbert spaces of different dimensionality d. We give explicit form of optimal cloning transformation for spin coherent states in the three-dimensional space, analytical results for the fidelity of the optimal cloning in $d=3\mathrm{}$ and $d=4\mathrm{}$ as well as numerical results for higher dimensions. In the low-dimensional case we construct the corresponding completely positive maps and exhibit their structure with the help of Jamiołkowski isomorphism. This allows us to formulate some conjectures about the form of optimal coherent cloning completely positive maps in arbitrary dimension.

We have observed emission spectra of excimers and exciplexes composed of a light alkali-metal atom in the first excited state and ${}^4\mathrm{He}$ atoms [${\mathrm{K}}^{*}{\mathrm{He}}_n$ $(n=1\mathrm{}-6),$ ${\mathrm{Na}}^{*}{\mathrm{He}}_n$ $(n=1\mathrm{}-4),$ and ${\mathrm{Li}}^{*}{\mathrm{He}}_n$ $\mathrm{}(n=1,2\mathrm{})\mathrm{}]$ in cryogenic He gas (the temperature $2\mathrm{K}<T<\mathrm{}100\mathrm{}\mathrm{K})$ in the spectral range from the atomic D lines to $6300{\mathrm{cm}}^{-1}.$ Differently from exciplexes with heavier alkali-metal atoms, the spectra for the different number of He atoms were well separated, so that their assignment could be made experimentally. Comparing with the spectra of ${\mathrm{K}}^{*}{\mathrm{He}}_n,$ we found that the infrared emission spectrum of the K atom excited in liquid He was from ${\mathrm{K}}^{*}{\mathrm{He}}_6.$ To confirm the assignment, we have also carried out ab initio calculation of adiabatic potential curves and peak positions of the emission spectra of the exciplexes.

A semiclassical model is used to investigate the possibility of selectively exciting one of two closely spaced, uncoupled Raman transitions. The duration of the intense pump pulse that creates the Raman coherence is shorter than the vibrational period of a molecule (impulsive regime of interaction). Pulse shapes are found that provide either enhancement or suppression of particular vibrational excitations.