Two-photon transitions from the ground state of atomic xenon gas, $\mathrm{Xe}{(}^1{S}_0),$ to ${\mathrm{Xe}}^{\mathrm{*}}$ $\mathrm{nf}$ and $\mathrm{np}$ Rydberg states have been excited in an apparatus that combines ion time-of-flight and photoelectron detection capabilities. Evidence is presented that shows that xenon atoms excited to $\mathrm{nf}$ states with $n=4\mathrm{}–8$ undergo rapid associative ionization with ground-state xenon atoms to form ${\mathrm{Xe}}_2^{+},$ while those excited to $\mathrm{np}$ states with $n=8\mathrm{}–11$ do not. Subsequent ${\mathrm{Xe}}_2^{+}$ dissociative recombination (DR) favors exit channels where xenon atoms are formed predominately in $6p$ and $5d$ excited states. Comparisons with older optical studies suggest that photoelectron spectroscopy provides a simple but effective means of studying short-time (ns) DR dynamics.

Triple differential cross sections (TDCS) have been studied for ionization of some heliumlike ions by fast electron impact in the coplanar geometry using a final-state correlated wave function that satisfies the asymptotic three-body boundary condition. The electron exchange effect between the two outgoing electrons in the final channel has also been incorporated properly. The initial channel wave function involves a Coulomb wave due to long-range Coulomb attraction between the incident electron and the screened ionic nucleus. TDCS have been computed in asymmetric geometry for a ${\mathrm{Li}}^{+}$ ion at different incident energies ${(E}_i)$ 150–1000 eV for fixed values of the ejected energies ${(E}_b=5\mathrm{}$ and 10 eV) and scattering angles $({\theta }_1=4\mathrm{}°$ and 10°). Symmetric geometry has also been studied for a ${\mathrm{Li}}^{+}$ ion for incident energies ${(E}_i=150\mathrm{}–500\mathrm{eV})$ for fixed scattering angle 45°. The behavior of the scaled TDCS ${(Z}_t^4\sigma )$ with respect to the variation of the ionic charge ${(Z}_t)$ for different ions in the helium isoelectronic series has been studied for asymmetric geometry at different incident energies in units of respective thresholds (3, 6, and 10) for a scaled ejected energy ${(E}_{\mathrm{bsc}})$ and a fixed scattering angle (4°), while for the symmetric geometry, scaled TDCS have been studied only at three times the respective threshold. The binary to recoil peak ratio $\mathrm{}(b/r)\mathrm{}$ is studied against the momentum transfer |q| in the asymmetric geometry for all the ionic targets. A strong recoil peak is noted at low incident energy for all the ions except for the ions of high charge (e.g., $Z_t=20).\mathrm{}$

We report electron-nuclear dynamics calculations of energy loss, charge exchange, and nuclear, electronic, and total stopping cross sections for protons and hydrogen atoms incident on atomic nitrogen, oxygen, and fluorine targets for projectile energies from a few eV up to 25 keV. Particular emphasis is placed on the analysis of the impact parameter and charge-exchange dependence of the energy loss. It is found that at low energies the electronic stopping is not proportional to the projectile speed, but depends on the excitation spectrum of the target, manifested by having a threshold or a second maximum in the stopping cross section at low projectile energy. Agreement with other calculations and the available experimental data is good.

Humberston [Can. J. Phys. 60, 591 (1982)], using the Kohn variational method, showed that the range of validity of Wigner’s threshold law for positronium formation in positron-hydrogen collisions is extremely narrow for the S wave. To examine the near-threshold behavior, we analyzed ab initio calculations using the multichannel effective range theory of Watanabe and Greene [Phys. Rev. A 22, 158 (1980)] and the single-channel effective range theory of Fabrikant [Opt. Spectrose 53, 131 (1982)] for the positronium-proton channel. We confirmed the presence of a Ramsauer minimum in the $L=0\mathrm{}$ elastic cross section for positronium-proton scattering, and found a similar minimum for $L=1.\mathrm{}$ The near-threshold structure is interpreted in terms of a virtual state, resonances, tunneling through and transmission over a barrier, and quantum suppression.

Some properties of the nonlinear coherent states (NCS), recognized by Vogel and de Matos Filho as dark states of a trapped ion, are extended to NCS on a circle, for which the Wigner functions are presented. These states are obtained by applying a suitable displacement operator $D_h\left(\alpha \right)$ to the vacuum state. The unity resolutions in terms of the projectors $|\alpha ,h〉〈\alpha {,h}^{-1}|,|\alpha {,h}^{-1}〉〈\alpha ,h|$ are presented together with a measure allowing a resolution in terms of $|\alpha ,h〉〈\alpha ,h|.$ $D_h\left(\alpha \right)$ is also used for introducing the probability distribution funtion ${\rho }_{A,h}\mathrm{}\left(z\right)\mathrm{}$ while the existence of a measure is exploited for extending the P representation to these states. The weight of the $n\mathrm{th}\mathrm{}$ Fock state of the NCS relative to a trapped ion with Lamb-Dicke parameter $\eta ,$ oscillates so wildly as n grows up to infinity that the normalized NCS fill the open circle ${\eta }^{-1}$ in the complex $\alpha$ plane. In addition, this prevents the existence of a measure including normalizable states only. This difficulty is overcome by introducing a family of deformations that are rational functions of n, each of them admitting a measure. By increasing the degree of these rational approximations, the deformation of a trapped ion can be approximated with any degree of accuracy and the formalism of the P representation can be applied.

Experiments have been carried out to study the dissociative ionization of a ${\mathrm{D}}_2$ molecule interacting with an intense linearly polarized two-color $(\omega +2\mathrm{}\omega )$ laser field. The response of the molecule to the individual laser fields at 800 and 400 nm indicate that at the shorter wavelength some of the molecules are dissociating in a direction perpendicular the polarization axis of the laser field, whereas such transitions are not observable at the longer wavelength. However, the perpendicular transitions seem to have been enhanced when both the laser pulses with their polarization axes parallel to each other are synchronously acting on the molecule. This observation was interpreted in terms of stronger coupling between $1s{\sigma }_g$ and the high lying $3d{\sigma }_g$ and $2p{\pi }_u$ electronic states of ${\mathrm{D}}_2^{+}$ when photons of the two colors are present. Investigations have also been carried out to study the response of the molecule with the polarization direction of the laser fields at ω and 2ω orthogonal to each other confirm the role of high-lying electronic states during the dissociative ionization of the ${\mathrm{D}}_2$ molecule.

Constructive procedures that make no use of optimization or iterative calculations for the control of many quantum and classical systems, via controls that are required to satisfy constraints on their power or pulse area, are presented. These procedures are based on structured decompositions of SU(2). A general technique for obtaining such structured decompositions is given. Illustrative examples are provided.

We report on a simple and versatile method by which to measure and tailor massive particle ensemble coherences using pulsed magnetic fields. A multiple wave atom interferometer is demonstrated that uses a spin-echo procedure associated with the spatial separation of the Zeeman sublevel wave packets induced by magnetic forces. This scheme provides a means to determine ultralow temperatures by measuring the sample coherence length. Furthermore, we show how a pulsed quasiparabolic magnetic potential can be used to enhance the atom ensemble coherence length by a factor of 2.

We present a quantum theory of the amplification of light undergoing a total internal reflection. We show that the light amplification is due to the stimulated emission of evanescent-mode photon from the active region of the interface. Our theoretical results are in good agreement with experimental observations and provide deeper understanding of the quantum-mechanical characteristics of the evanescent wave. A corresponding triplet-mode laser theory is also presented.

We report a different mechanism to generate x-ray transients by exploiting high-field nonperturbative subcarrier-wave coherent phenomena. The interaction of several-cycle optical pulses with a nonlinear material results in carrier-wave Rabi flopping that acts as an alternative source for x-ray generation.

A numerical probing technique is proposed that can resolve the spectral structures of high-order harmonics obtained from the solutions of the Schrödinger equation. This method can accurately locate the high harmonics in the frequency domain, which otherwise might be impossible due to the intricate structures of midplateau harmonics in the short drive pulse regime. Resolved fine spectra reveal that the high harmonics contain several components whose phases have different intensity dependences, in accordance with the prediction of semiclassical approaches. The present technique is applied to the measurement of the harmonic blueshift induced by intense femtosecond pulses.

The dynamics of Josephson-like oscillations between two coupled Bose-Einstein condensates is studied using the time-dependent variational method. We suppose that the quantum state of the condensates is a Gaussian wave-packet which can translate and perform breathing shape oscillations. Under this hypothesis we study the influence of these degrees of freedom on the tunneling dynamics by comparing the full-model with one where these degrees of freedom are “frozen” at its equilibrium values. The result of our calculation shows that when the traps are not displaced the two models agree, whereas when they are, the models differ considerably, the former being now closer to its linear approximation.

Magnetic properties of ${\mathrm{Dy}}_N$ clusters in a molecular beam generated with a liquid-helium–cooled nozzle are investigated by Stern-Gerlach experiments. The cluster magnetizations ${\mu }_z$ are measured as a function of magnetic field $(B=0\mathrm{}–1.6$ T) and cluster size $(17\mathrm{}<~N<~55).$ The most important observation is the saturation of the magnetization ${\mu }_z\mathrm{}\left(B\right)\mathrm{}$ at large field strengths. The magnetization approaches saturation following the power law $|{\mu }_z-{\mu }_0|\sim 1/\sqrt{B},$ where ${\mu }_0$ denotes the magnetic moment. This gives evidence for adiabatic magnetization.

We show how to extract approximate, yet accurate, density-of-states information over a continuous range of energies from a finite symmetric Hamiltonian matrix H. The approximation schemes that we present make use of the theory of orthogonal polynomials associated with tridiagonal matrices. We demonstrate the merits of the methods by applying them to problems with single, double, and multiple density bands, as well as to a problem with infinite spectrum and to that of a particle in a potential field.

We show that the recently discovered universal upper bound on the thermal conductance of a single channel comprising particles obeying arbitrary fractional statistics is in fact a consequence of a more general universal upper bound, involving the averaged entropy and energy currents of a single channel connecting heat reservoirs with arbitrary temperatures and chemical potentials. The latter upper bound in turn leads, via Holevo’s theorem, to a universal (i.e., statistics-independent) upper bound on the optimum capacity for classical information transmission down a single, wideband quantum channel.

I consider Lagrangians which depend nonlocally in time but in such a way that there is no mixing between times differing by more than some finite value $\Delta t.\mathrm{}$ By considering these systems as the limits of ever higher derivative theories, I obtain a canonical formalism in which the coordinates are the dynamical variable from t to $t+\Delta t.\mathrm{}$ A simple formula for the conjugate momenta is derived in the same way. This formalism makes apparent the virulent instability of this entire class of nonlocal Lagrangians. As an example, the formalism is applied to a nonlocal analog of the harmonic oscillator.

I investigate whether it would technologically and economically make sense to build database search engines based on Grover’s quantum search algorithm. The answer is not fully conclusive but in my judgement rather negative.

We present models of quantum gates based on coupled quantum dots in which a qubit is regarded as the superposition of ground states in each dot. Coherent control on the qubit is performed by a monochromatic light pulse illuminated on the quantum dots. Considering particular types of artificial molecules, we show that the qubit is easily manipulated with the polarization and frequency of a light pulse and, especially, the controlled-NOT operation can be possible exploiting the electron-electron interaction. To examine the decoherence of quantum states, we discuss electronic relaxation contributed mainly by LA phonon processes.

Rules for obtaining transition amplitudes that are equal in length form and velocity form, order-by-order in relativistic many-body perturbation theory are presented. Explicit formulas are derived for first-, second-, and third-order amplitudes for transitions between valence states in alkali-metal atoms. Numerical codes are developed to evaluate amplitudes through third order and applied to $3s-{3p}_{1/2}$ and $3s-{3p}_{3/2}$ transitions in sodium and sodiumlike ions. The present calculations for sodiumlike ions are compared with other accurate theoretical calculations.

We report optical double-resonance spectroscopy to locate and study the ${7D}_{3/2}$ and ${7D}_{5/2}$ levels of a sample of ${}^{210}\mathrm{Fr}$ atoms confined and cooled in a magneto-optical trap. The upper state of the ${7P}_{3/2}$ trapping transition serves as the resonant intermediate level to reach the $7D$ states. The energy difference to the ground state is measured for the accessible levels. We measure the hyperfine splittings: $\Delta {(7D}_{3/2},F=15/2\mathrm{}\leftrightarrow 13/2)=167\pm 4\hspace{0.5em}\mathrm{MHz},$ $\Delta {(7D}_{5/2},F=17/2\mathrm{}\leftrightarrow 15/2)=-117.5\pm 2.5\hspace{0.5em}\mathrm{MHz},$ and $\Delta {(7D}_{5/2},F=15/2\mathrm{}\leftrightarrow 13/2)=-121\pm 4$ MHz. Extrapolating the energies of the inaccessible hyperfine levels from the hyperfine constants and assuming ${B(7D}_{3/2})=0,$ the center-of-gravity energy difference to the ground state is ${E(7D}_{3/2})=24\mathrm{}244.831\pm 0.003\hspace{0.5em}{\mathrm{cm}}^{-1}$ and ${E(7D}_{5/2})=24\mathrm{}333.298\pm 0.003\hspace{0.5em}{\mathrm{cm}}^{-1}.$