State-selective single-electron capture in slow collisions of ${\mathrm{He}}^{2+}$ ions with ${\mathrm{O}}_2$ has been studied experimentally at laboratory impact energies between 0.1 and 1.0 keV by means of the translational energy-gain spectroscopy technique. The translational energy spectrum clearly shows that the dominant reaction channel is due to dissociative single-electron capture [single-electron capture into ${\mathrm{He}}^{+}\mathrm{}(n=1\mathrm{})\mathrm{}$ with target ionization, i.e., transfer ionization] at low energies, whereas contributions from capture into the ${\mathrm{He}}^{+}\mathrm{}(n=2\mathrm{})\mathrm{}$ state with the production of ${\mathrm{O}}_2^{+}$ in the ground state $\left(X{}^2{\Pi }_g\right)$ (nondissociative single-electron capture) increase as the collision energy is increased and becomes the dominant process at collision energies $E>~0.7\hspace{0.5em}\mathrm{keV}.$ The energy dependence of total cross sections for single-electron capture is also measured and found to slowly increase with increasing collision energies.

Electromagnetically induced output coupling of a trapped Bose-Einstein gas at finite temperatures into propagating or bound matter waves is equivalent in many ways to molecular processes such as photodissociation at finite temperature. We develop a semiclassical approximation for the transfer rate of a thermal distribution of atoms or molecules between two potential surfaces under the influence of an external electromagnetic field. To leading order, the result is an integral over phase space, restricted by energy conservation and weighted by the initial thermal phase-space distribution. The validity of the method is demonstrated by a set of examples. Applying the theory to the case of weak output coupling of a magnetically trapped atomic Bose-Einstein gas at finite temperature into a loosely confined or unconfined state, we give quantitative predictions for the spectrum of transition rates in real situations. An asymmetric broadening of the spectrum of transitions relative to the expected spectrum of transitions at zero temperature is obtained, which may be related to the asymmetric spectral broadening observed recently in a similar situation.

In this paper we consider the mechanism of coherent control of atomic collisions by two-photon excitation of colliding atoms with nonclassical light characterized by polarization entanglement. Such modification of the well-known optical-collision method is proposed as a possible spectroscopic application of nonclassical light for study of collisional dynamics. We show that quantum correlations allow one to have a deeper control of the internal dynamics of atomic collision than do the principles of classical statistics. Our qualitative discussion is supported by numerical calculations made for ${}^1{S}^1{P}^{1}S$ optical transition of Mg perturbed by collisions with rare-gas atom.

Clock synchronization procedures are analyzed in the presence of imperfect communications. In this context we show that there are physical limitations, which prevent one from synchronizing distant clocks when the intervening medium is completely dephasing, as in the case of a rapidly varying dispersive medium.

A feasible device for measurement of fidelity, overlap, purity, and Hilbert-Schmidt distance of two mixed states is proposed. In addition, this device realizes a decomposable entanglement witness-measurement for bipartite systems, corresponding to Werner criterion of entanglement. The measurement, based on interferometric setup and the control-phase gate, can be directly implemented in the cavity quantum electrodynamics, trapped ion, and electromagnetically induced transparency experiments.

The theory of time- and frequency-gated (TFG) spontaneous emission (SE) spectra is elaborated. The present formulation generalizes previous derivations, clarifies the interrelations between different existing expressions, and establishes the validity of certain commonly assumed approximations. We obtain various explicit expressions for TFG SE spectra, which are suitable for performing actual calculations for nontrivial systems and which allow us to establish generic (that is, model-independent) properties of TFG spectra. The doorway-window picture of temporally and spectrally resolved spectra is further developed. It is shown that, to the leading order in the pump and probe pulses, the TFG SE signal is equivalent to the stimulated-emission contribution to the integral pump-probe spectrum in the case of nonoverlapping pulses. The theory is illustrated for the example of an electronic two-level system with a single Condon-active harmonic vibrational mode that is coupled to a thermal bath. The effect of imperfect time and frequency resolution is studied. It is pointed out that the TFG SE spectrum carries information not only on the strength of the system-bath coupling, but also on the relative magnitude of the bath correlation time.

An experimental and theoretical investigation of lifetimes of metastable levels in La II has been performed. The experimentally obtained results using the laser probing of a stored ion beam were $\tau =5.2\mathrm{}\pm 0.2\mathrm{s}$ for the $a^1{G}_4$ and $\tau =2.1\mathrm{}\pm 0.3\mathrm{s}$ for the $b^1{D}_2$ levels. Within the error bars, the results are in good agreement with the relativistic Hartree-Fock calculations including core polarization.

Ar photoionization is studied using the R-matrix formalism with emphasis on the simultaneous excitation of the residual ${\mathrm{Ar}}^{+}$ ion. Cross sections have been obtained for excitation of the ${3p}^4\mathrm{}(3d,4s,4p)\mathrm{}$ states. A comparison with experiments having a resolution of 70 meV shows reasonable agreement for the position and shape of resonance structures. The relative magnitude of the resonances proves to be more elusive. The partial cross section for excitation of the ${3p}^4{(}^3{P}^e)4p{}^2{P}_{3/2}^o$ and ${}^2{D}_{3/2}^o$ levels is treated in more detail. A comparison of $\mathrm{LS}$-coupling calculations with high-resolution experimental results shows good agreement for both the excitation cross sections and the polarization of the fluorescence. We also predict the orientation for both levels. We demonstrate that the polarization of the fluorescence originating from the ${}^2{D}_{3/2}^o$ level can be employed to study spin-orbit effects in Ar photoionization.

Nonadiabatic tunneling is an effect occurring when two potentials are crossing each other with opposite slopes. It is characterized by the vanishing of the transmission probability at a set of energies (or nodes) that can be identified as the resonance energies of the system. We investigate the modification of this probability induced by the interaction of the particle with an oscillating field. The main result of this study is the presence of additional dips in the transmissivity, representing replicas of the nodal structure. They are due to processes implying an absorption (or emission) followed by an emission (or absorption) of one or even more than one quantum.

The T-matrix approach, as formulated by Pindzola et al. [Phys. Rev. A 62, 062718 (2000)] for calculating the single-differential ionization cross section (SDCS) has been further investigated. Using the “intermediate-energy R-matrix method” to obtain the full scattering wave function needed in the matrix element, we performed several case studies for the Temkin-Poet S-wave model of e-H scattering to study the dependence of the results on the box radius and the number of states included. Despite encouraging results before reaching convergence, we conclude that the method will ultimately not yield the correct form of the SDCS but instead will still suffer from unphysical oscillations.

Light-induced drift (LID) of a rarefied gas in a cell with flat-plate geometry is studied in the limits of large length and width of the cell, and exact solutions to the model rate equations are obtained, with exact analytical solutions for the case of surface LID (SLID); the special case of the limit of low radiation absorption by the gas in SLID is given particular attention. Many results are different from those of previous work. Emphasis is placed on considerations of comparison with experiment.

Light-induced drift (LID) of a rarefied gas in a cell with circular-cylindrical geometry is studied, and exact solutions to the model rate equations are obtained, with exact analytical solutions for the case of surface LID (SLID); the special case of the limit of low radiation absorption by the gas in SLID is given particular attention. Many results are different from those of previous work. Emphasis is placed on considerations of comparison with experiment. This is part II of a series of papers, part I having studied LID with flat-plate geometry [F. O. Goodman, preceding paper, Phys. Rev. A 65, 063409 (2002)].

We show that it is possible to entangle three different many-particle states by Bragg spectroscopy with nonclassical light in a Bose condensate of weakly interacting atomic gases. Among these three states, two are of atoms corresponding to two opposite momentum side modes of the condensate; and the other is of single-mode photons of the output probe beam. We demonstrate strong dependence of the multiparticle entanglement on the quantum statistics of the probe light. We present detailed results on entanglement keeping in view the possible experimental situation.

The process of stimulated Raman adiabatic passage (STIRAP) provides a possible route for the generation of a coherent molecular Bose-Einstein condensate (BEC) from an atomic BEC. We analyze this process in a three-dimensional mean-field theory, including atom-atom interactions and nonresonant intermediate levels. We find that the process is feasible, but at larger Rabi frequencies than anticipated from a crude single-mode lossless analysis, due to two-photon dephasing caused by the atomic interactions. We then identify optimal strategies in STIRAP allowing one to maintain high conversion efficiencies with smaller Rabi frequencies and under experimentally less demanding conditions.

We demonstrate theoretically that periodically poled materials with a suitable poling period can strongly reduce all ${\chi }^{\mathrm{}\left(2\right)\mathrm{}}:{\chi }^{\mathrm{}\left(2\right)\mathrm{}}$ cascading during ${\chi }^{\mathrm{}\left(3\right)\mathrm{}}$ third-harmonic generation and optical parametric amplification in noncentrosymmetric crystals: the calculated reduction is, respectively, 3 and 6 orders of magnitude along the X axis of ${\mathrm{KTiOPO}}_4.$ This is then an original and promising way to achieve efficient pure cubic optical frequency conversion, for the study of three-photon quantum properties.

For quantum-mechanical entangled states we introduce the entangled Wigner operator in the entangled-state representation. We derive the time evolution equation of the entangled Wigner operator. The trace product rule for entangled Wigner functions is also obtained.

We identify discrepancies between two published predictions of the resonance fluorescence from a two-level atom driven by a strong bichromatic field [J. Opt. Soc. Am. B $8,$ 1163 (1991) and Phys. Rev. A $48,$ 3092 (1993)]. These discrepancies are shown to arise from subtleties in extracting the time-averaged resonance fluorescence from the expansions used to solve the optical Bloch equations. We construct a solution to these equations that corrects the results of the latter reference and reconciles the two predictions.

A set of generalized coherent states for the one-dimensional Coulomb problem in coordinate representation is constructed. At first, we obtain a mapping for proper transformation of the one-dimensional Coulomb problem into a nonrotating four-dimensional isotropic harmonic oscillator in the hyperspherical space, and the generalized coherent states for the one-dimensional Coulomb problem is then obtained in exact closed form. This exactly soluble model can provide an adequate means for a quantum coherency description of the Coulomb problem in one dimension, sample for coherent aspects of the exciton model in one-dimension example in high-temperature superconductivity, semiconductors, and polymers. Also, it can be useful for investigating the coherent scattering of the Coulomb particles in one dimension.

In this paper we present an optimal protocol by which an unknown state on a Hilbert space of dimension N can be approximately stored in an M-dimensional quantum system or be approximately teleported via an M-dimensional quantum channel. The fidelity of our procedure is determined for pure states as well as for mixed states and states that are entangled with auxiliary quantum systems of varying Hilbert-space dimension, and it is compared with theoretical results for the maximally achievable fidelity.

We present a protocol to generate and control quantum entanglement between the states of two subsystems (the system $\mathcal{S})$ by making measurements on a third subsystem (the monitor $\mathcal{M}),$ interacting with $\mathcal{S}.$ For the sake of comparison we consider first an ideal, or instantaneous projective measurement, as postulated by von Neumann. Then we compare it with the more realistic or generalized measurement procedure based on photocounting on $\mathcal{M}.$ Further we consider that the interaction term (between $\mathcal{S}$ and $\mathcal{M})$ contains a quantum nondemolition variable of $\mathcal{S}$ and discuss the possibility and limitations for reconstructing the initial state of $\mathcal{S}$ from information acquired by photocounting on $\mathcal{M}.$