A new systematic method is presented to construct a correlation energy functional in the density-matrix functional theory. A new exact relation, particle-hole symmetry, is presented, which states that the exact functional gives the same correlation energy for the first-order reduced density matrix (1-RDM) and the corresponding hole 1-RDM. Nakatsuji’s density equations of the first and the second orders together with the decoupling approximation of the 3- and 4-RDMs are solved numerically to examine the properties of the correlation energy functional. This functional, defined as the solution of the set of equations, satisfies Levy’s homogeneous coordinate scaling and the particle-hole symmetry and reproduces about 95% of the correlation energies of several molecules. By expanding these equations in perturbation series the leading term of the correlation energy functional is identified. Numerical analysis shows that this simplified functional, which contains one fitting parameter, reproduces the energies of several molecules accurately. The direction of further study is discussed.

We have measured the total cross sections for electron capture by bare ${\mathrm{Pb}}^{82+}$ ions and for the ionization of hydrogenlike ${\mathrm{Pb}}^{81+}\mathrm{}\left(1s\right)\mathrm{}$ ions at $158\mathrm{G}\mathrm{e}\mathrm{V}/\mathrm{A},$ $\gamma =168,$ in Ar, Kr, and Xe gas targets. At this energy, the total capture cross sections are dominated by electron capture from pair production. The capture measurements are compared with the results of several theoretical calculations and with similar measurements made with solid targets. The ${\mathrm{Pb}}^{81+}\mathrm{}\left(1s\right)\mathrm{}$ ionization cross sections obtained, which are substantially lower than those measured in solids, agree well with recent calculations that predict saturation at high energies from target screening effects.

Photoionization of Xe atoms is investigated close to the maximum of the $4d$ shape resonance by means of spin-resolved photoelectron spectroscopy. Using circularly and linearly polarized synchrotron radiation of 93.8-eV energy, we investigate the photoionization processes of the $5p,$ $5s,$ and $4d$ shells. By combination of earlier data for the partial and differential cross sections with our measurements, we are able to perform a complete characterization of the Xe $4d$ photoionization process, i.e., we can determine all the relativistic dipole matrix elements. Comparison with different theoretical calculations shows the importance of relaxation effects at this photon energy.

We study the bound-free electron-positron pair production in relativistic heavy-ion collisions to different bound states in a full plane-wave Born approximation calculation. Exact Dirac wave functions are used for both the bound electron and the free positron in the final states. Results for the relativistic heavy-ion collider as well as the forthcoming large hadron collider are given. This process is one of the dominant beam loss processes and can become critical for the operation with heavy ions. A simple parametrization is given as well. We compare our results with calculations of other groups.

A distorted-wave theory is developed in which the effect of long-range multipole potentials, having off-diagonal elements in channel space, is accounted for in the construction of asymptotic states. The theory may be applied to the scattering of an electron by a polarizable atomic system carrying a net positive charge and a permanent quadrupole moment. The current treatment is confined to such a system, though greater generality is possible. Asymptotic states are introduced in the form of a superposition of Coulomb wave functions with expansion coefficients determined by means of a modified perturbation theory. Analytic properties of the basis functions are preserved in this expansion and this allows, in the spirit of effective-range theory, for the determination of the energy dependence of the scattering matrix in the neighborhood of reaction thresholds. In particular, the Rydberg series of resonances that appears just below the energy for the opening of a new channel, well described by standard quantum-defect theory, is exhibited for the extended model scattering system considered here.

The ${3d}_{5/2}\to$ $6p$ and $7p$ excitations and their decay in Xe have been studied by using total ion yield and angle-resolved electron spectroscopies. The natural linewidths of the ${3d}_{5/2}^{-1}\mathrm{np}\mathrm{}(n=6,7\mathrm{})\mathrm{}$ states were determined. Anisotropy parameters of resonant Auger transitions to ${4d}^{-2}\mathrm{np}\mathrm{}(n=6,7\mathrm{})\mathrm{}$ final states were extracted from the experiment. They were found to be connected with the anisotropy parameters of the corresponding normal Auger transitions as predicted by the gross spectator model.

Using a recently developed multicoincidence technique, fragmentation resulting from collisions between high energy $(60\mathrm{}\hspace{0.5em}\mathrm{k}\mathrm{e}\mathrm{V}/\mathrm{u})$ ${\mathrm{H}}_{27}^{+}$ ions with an He target are investigated on an event by event basis. The data obtained are analyzed in terms of fluctuations in the fragment size distribution. A comparison with results from two different three-dimensional (3D) lattice bond percolation models of the same size (27 constituents) indicates the presence of a critical behavior in the decaying finite system and the importance of accounting in the percolation model for the specific binding situation in the hydrogen cluster ion.

Dielectric atomic mirrors are considered in which the repulsive force field owes its existence to an evanescent mode in the presence of a metallic capping layer. The theory of such an atomic mirror is constructed, assuming a finite thickness of the metallic layer with a finite plasma frequency and adopting the field-dipole orientation picture. The Rabi frequency together with the reflectivity for the light incident from within the substrate are evaluated, and their variations with the type of metal and layer thickness analyzed as useful indicators of the effectiveness of the system as an atomic mirror. A number of interesting features are pointed out, including a desirable enhancement. Solutions of the equation of motion for a given atom, subject to given initial conditions, lead to trajectories exhibiting reflection. The leading force fields controlling the dynamics include the average dipole image force plus the average light-induced forces due to the evanescent field. The parameters used to compute the trajectories are similar to those in recent experiments in which Rb atoms incident on a silver film deposited on a glass substrate have been shown to experience enhanced mirror action. The factors controlling the enhancement in general are pointed out and discussed.

Starting from the quantum kinetic equation for the noncondensate atoms and the generalized Gross–Pitaevskii equation for the condensate, we derive the two-fluid hydrodynamic equations of a trapped Bose gas at finite temperatures. We follow the standard Chapman–Enskog procedure, starting from a solution of the kinetic equation corresponding to the complete local equilibrium between the condensate and the noncondensate components. Our hydrodynamic equations are shown to reduce to a form identical to the well-known Landau-Khalatnikov two-fluid equations, with hydrodynamic damping due to the deviation from local equilibrium. The deviation from local equilibrium within the thermal cloud gives rise to dissipation associated with shear viscosity and thermal conduction. In addition, we show that effects due to the deviation from the diffusive local equilibrium between the condensate and the noncondensate (recently considered by Zaremba, Nikuni, and Griffin) can be described by four frequency-dependent second viscosity transport coefficients. We also derive explicit formulas for all the transport coefficients. These results are used to introduce two new characteristic relaxation times associated with hydrodynamic damping. These relaxation times give the rate at which local equilibrium is reached and hence determine whether one is in the two-fluid hydrodynamic region.

The present paper treats the electromagnetically induced transparency (EIT), i.e., the absorption spectrum of a weak probe field, near-resonant to a material transition, in the presence of a strong amplitude-phase fluctuating field which couples the upper level of the transition to another excited level. The coupling field is assumed to be chaotic (i.e., a complex Gaussian process with a Lorentzian spectrum) and so strong that the material relaxation and the detuning can be neglected. In addition, we consider the Fourier transform of the spectrum $U_{\mathrm{aa}}\mathrm{}\left(t\right),$ which determines absorption of a probe field with a time-dependent intensity. The quantity $U_{\mathrm{aa}}\mathrm{}\left(t\right)\mathrm{}$ equals a diagonal element of the average reduced evolution operator of the two-level system (TLS), coupled by the strong field. As a starting point, we use the stationary, partially averaged stochastic Schrödinger equation, which has the form of a set of two second-order differential equations. The theory is developed by combining analytical and numerical approaches. For the most important regime, when the rms Rabi frequency $V_0$ is much greater than the coupling-field bandwidth $\nu ,$ we obtain scaling relations for the EIT line shape and the TLS evolution. In particular, the absorption at the minimum (i.e., at the resonance frequency) scales as ${\nu }^{1/3}{V}_0^{-4/3},$ whereas the evolution function $U_{\mathrm{aa}}\mathrm{}\left(t\right)\mathrm{}$ performs damped oscillations with the decay rate on the order of ${(V}_0^2\nu {)}^{1/3}.$ These results differ significantly from those following from the uncorrelated-jump model. The results of this paper are shown to be applicable to more general models of amplitude-phase fluctuations than the Gaussian-Markovian chaotic field.

We seek to analyze, employing stochastic differential equations, the squeezing and statistical properties of the light generated by a three-level laser whose cavity contains a parametric amplifier. It is found that the effect of the parametric amplifier is to increase the intracavity squeezing by a maximum of 50%.

The quantum channel subject to local interaction with two-level environment is studied. The two-level environment is regarded as a quantum bit (qubit) as well as a pair of particles owned by Alice and Bob. The amount of entanglement initially shared by Alice and Bob is distributed among these three qubits due to the interaction. In this model, we show that the singlet fraction of the decohered quantum channel is uniquely determined by the distributed entanglement. When the decohered quantum channel is used under the standard teleportation scheme, the optimal teleportation fidelity is well understood by considering the remaining entanglement between environment and transmitted state.

The change of saturated absorption spectra of the Cs $D_2$ line were measured with the pump beam intensity. The line shapes of the resonance signals, especially for the cyclic transition $F=\overrightarrow{4}{F}^{\prime }=5,$ were very sensitive to the pump beam intensity. We suggested a simple model that phenomenologically describes the change of the line shape of the resonance signal with the pump beam intensity.

In a recent paper [A. Cabello, Phys. Rev. A 61, 052312 (2000)], a quantum key distribution protocol based on entanglement swapping was proposed. However, in this Comment, it is shown that this protocol is insecure if Eve uses a special strategy to attack.

The difficulty noted in the preceding Comment can be avoided by a modification detailed in a forthcoming Addendum in Physical Review A [A. Cabello (to be published)].

We propose probabilistic controlled-NOT and controlled-phase gates for qubits stored in the polarization of photons. The gates are composed of linear optics and photon detectors, and consume polarization entangled photon pairs. The fraction of the successful operation is only limited by the efficiency of the Bell-state measurement. The gates work correctly under the use of imperfect detectors and lossy transmission of photons. Combined with single-qubit gates, they can be used for producing arbitrary polarization states and for designing various quantum measurements.

A kinematically complete experiment on single ionization for 75-keV ${\mathrm{H}}_2^{+}+\mathrm{H}\mathrm{e}$ collisions was performed by measuring the fully momentum analyzed projectiles and recoil ions in coincidence. The electron momentum was deduced from momentum conservation. Clear signatures of the postcollision interaction between the outgoing projectiles and the electrons were observed in the momentum spectra of all collision products simultaneously.

We present a method of coupling laser-cooled atoms from a vapor-cell magneto-optic trap (MOT) into a magnetic atom guide. The axis of the four-wire quadrupole guide passes directly through the center of the MOT. The guide is tilted at a small angle with respect to the horizontal plane to facilitate the propagation of the atoms released from the MOT into the guide. We demonstrate the loading of ${10}^5{\hspace{0.5em}}^{87}\mathrm{Rb}$ atoms into the guide and measure their propagation up to distances of 17 cm (limited by the guide length). The guide incorporates a tapered section in which the guide diameter reduces by a factor of about 3.

We analyze adiabatic transfer processes in two-level systems driven by bichromatic delayed laser pulses. We show that the robust transfer of atomic population and the exchange of momentum with the laser fields can be understood on the basis of topological properties of dressed energy surfaces that are determined by dynamical resonances. The analysis shows a topological quantization of the multiple absorption and emission of photons.

We report on the creation of Bose-Einstein condensates of ${}^{87}\mathrm{Rb}$ in a specially designed hybrid, optical dipole and magnetic trap. This trap naturally allows the coherent transfer of matter waves into a pure optical dipole potential waveguide based on a doughnut beam. Specifically, we present studies of the coherence of the ensemble in the hybrid trap and during the evolution in the waveguide by means of an autocorrelation interferometer scheme. We observe a mean-field dominated acceleration in the waveguide on a much longer time scale than in the free three-dimensional expansion.