Ab initio theory is developed for radiative transitions between excited states of neon. Calculations of energies for even excited states $J=1,$ $J=2\mathrm{}$ supplement our previous calculations for $J=1\mathrm{}$ odd excited states. Line strengths for transitions between $J=1\mathrm{}$ odd and $J=1,2\mathrm{}$ even states of Ne I are evaluated. A comparison with experiments and semiempirical calculations is given.

By using a Hylleraas configuration-interaction explicitly correlated expansion we compute an upper bound to the energy of the ${2p}^2$ ${}^3{P}^e$ bound state of ${\mathrm{H}}^{-}.$ The result is converged on eleven significant digits. It improves the previous best upper bound on the sixth significant figure.

Nondipole asymmetries of Kr $1s$ photoelectrons were measured over the 11–8000 eV kinetic-energy range. Symmetry properties of angular distributions were exploited to eliminate the dependence of the measurements on the dipole anisotropy and the polarization properties of the photon beam. The measured asymmetries agree well with both full multipole relativistic and nonrelativistic first-order retardation calculations within the independent-particle approximation. Deviations of the measured asymmetries from predictions of the point-Coulomb retardation correction confirm the importance of screening on the continuum-wave normalizations and phase shifts.

In a previous work [Phys. Rev. A 66, 013410 (2002)], we noted a partial disagreement between quantum R matrix and semiclassical calculations of photoabsorption spectra of molecules in a magnetic field. We show that this disagreement is due to a nonvanishing contribution of processes, which are forbidden according to the usual semiclassical formalism. Formulas to include these processes are obtained by using a refined stationary phase approximation. The resulting higher order in $ħ$ contributions also account for previously unexplained “recurrences without closed orbits.” Quantum and semiclassical photoabsorption spectra for Rydberg atoms and molecules in a magnetic field are calculated and compared to assess the validity of the first-order forbidden orbit contributions.

We study the scissors mode of a free-expanding Bose-Einstein condensate. We find that the irrotational character of the superfluid flow within the condensate has dramatic consequences on the evolution of the scissors oscillation. After a short expansion the oscillation is amplified and distorted, while asymptotically it recovers its initial sinusoidal behavior, with an enhanced amplitude. We investigate this phenomenon by using a technique to excite the scissors mode in a condensate held in a magnetostatic potential.

We present closed analytical expressions for the particle and kinetic-energy spatial densities at finite temperatures for a system of noninteracting fermions (bosons) trapped in a d-dimensional harmonic-oscillator potential. For $d=2\mathrm{}$ and $3,$ exact expressions for the N-particle densities are used to calculate perturbatively the temperature dependence of the splittings of the energy levels in a given shell due to a very weak interparticle interaction in a dilute Fermi gas. In two dimensions, we obtain analytically the surprising result that the l degeneracy in a harmonic-oscillator shell is not lifted in the lowest order even when the exact, rather than the Thomas-Fermi expression for the particle density is used. We also demonstrate rigorously (in two dimensions) the reduction of the exact zero-temperature fermionic expressions to the Thomas-Fermi form in the large-N limit.

An asymptotically exact many-body theory for spin-polarized interacting fermions in a one-dimensional harmonic atom trap is developed using the bosonization method and including backward scattering. In contrast to the Luttinger model, backscattering in the trap generates one-particle potentials which must be diagonalized simultaneously with the two-body interactions. Inclusion of backscattering becomes necessary because backscattering is a dominant interaction process between confined identical one-dimensional fermions. The bosonization method is applied to the calculation of one-particle matrix elements at zero temperature. A detailed discussion of the validity of the results from bosonization is given, including a comparison with direct numerical diagonalization in fermionic Hilbert space. A model for the interaction coefficients is developed along the lines of the Luttinger model with only one coupling constant K. With these results, particle densities, the Wigner function, and the central pair-correlation function are calculated and displayed for large fermion numbers. It is shown how interactions modify these quantities. The anomalous dimension of the pair-correlation function in the center of the trap is also discussed and found to be in accord with the Luttinger model.

We show that utmost possible Raman coherence between equally populated levels can be excited by two-photon resonant bichromatic field far from one photon resonance by means of relaxation processes. On this basis we suggest a mechanism for generation of extremely short pulses with high pulse duty factor and large energy in the pulse. It can be realized in solid materials, such as the rare-earth doped dielectrics with long-lived spin coherence or nitrogen-vacancy $\mathrm{}(N-V)\mathrm{}$ centers in diamond and provide a simple, reliable, and convenient technique for many practical applications.

The generation of an entangled coherent state is one of the most important ingredients of quantum information processing using coherent states. Recently, numerous schemes to achieve this task have been proposed. In order to generate travelling-wave entangled coherent states, cross-phase-modulation, optimized by optical Kerr effect enhancement in a dense medium in an electromagnetically induced transparency (EIT) regime, seems to be very promising. In this scenario, we propose a fully quantized model of a double-EIT scheme recently proposed [D. Petrosyan and G. Kurizki, Phys. Rev. A 65, 33 833 (2002)]: the quantization step is performed adopting a fully Hamiltonian approach. This allows us to write effective equations of motion for two interacting quantum fields of light that show how the dynamics of one field depends on the photon-number operator of the other. The preparation of a Schrödinger cat state, which is a superposition of two distinct coherent states, is briefly exposed. This is based on nonlinear interaction via double EIT of two light fields (initially prepared in coherent states) and on a detection step performed using a 50:50 beam splitter and two photodetectors. In order to show the entanglement of an entangled coherent state, we suggest to measure the joint quadrature variance of the field. We show that the entangled coherent states satisfy the sufficient condition for entanglement based on quadrature variance measurement. We also show how robust our scheme is against a low detection efficiency of homodyne detectors.

In this paper, using the decomposition theorem of superoperators, we present a general method to solve master equations with superoperator generators of su(1,1) and su(2) Lie algebras. With the help of this method, the time evolution of the density operators for certain systems, which have SU(1,1) and SU(2) symmetry, can be easily obtained from any given initial state.

Quantum-cryptography key distribution (QCKD) experiments have been recently reported using polarization-entangled photons. However, in any practical realization, quantum systems suffer from either unwanted or induced interactions with the environment and the quantum measurement system, showing up as quantum and, ultimately, statistical noise. In this paper, we investigate how an ideal polarization entanglement in spontaneous parametric down-conversion (SPDC) suffers quantum noise in its practical implementation as a secure quantum system, yielding errors in the transmitted bit sequence. Since all SPDC-based QCKD schemes rely on the measurement of coincidence to assert the bit transmission between the two parties, we bundle up the overall quantum and statistical noise in an exhaustive model to calculate the accidental coincidences. This model predicts the quantum-bit error rate and the sifted key and allows comparisons between different security criteria of the hitherto proposed QCKD protocols, resulting in an objective assessment of performances and advantages of different systems.

The relative differential partial ionization cross sections for the production of ionic fragments of ${\mathrm{SF}}_6$ molecule under impact of 10–20 keV electrons have been measured using an ejected electron-produced ion coincidence technique in a crossed beam apparatus with a time-of-flight analysis of the ions. The detection angle of the ejected electrons of nondiscriminated energies was kept at 90° with respect to the incident electron-beam direction. The 14 ionic fragments: ${\mathrm{SF}}_5^{+},$ ${\mathrm{SF}}_4^{+},$ ${\mathrm{SF}}_3^{+},$ ${\mathrm{SF}}_2^{+},$ ${\mathrm{SF}}^{+},$ ${\mathrm{S}}^{+},$ ${\mathrm{F}}^{+},$ ${\mathrm{SF}}_4^{2+},$ ${\mathrm{SF}}_3^{2+},$ ${\mathrm{SF}}_2^{2+},$ ${\mathrm{S}}^{2+},$ ${\mathrm{F}}^{2+},$ ${\mathrm{SF}}_3^{3+},$ and ${\mathrm{S}}^{3+}$ resulting from the dissociative ionization of the ${\mathrm{SF}}_6$ molecule were identified and their relative production cross sections have been measured. The branching ratios of 8 ionic fragments ${\mathrm{SF}}_m^{n+}$ $(m=1\mathrm{}$ to 5 and $n=1\mathrm{}$ to 3) as a function of impact energy have been determined. These ratios are found to have an almost a constant value over the considered impact energy range within the experimental uncertainty of the measurements. For the investigated impact energies, no previous data or theoretical calculations exist for a direct comparison with the present results.

The Coulomb excitation of inner-shell electrons around heavy and highly charged projectile ions impinging on light targets is investigated in the highly relativistic energy regime for projectiles as heavy as gold $\mathrm{}(Z=79\mathrm{}).$ First-order time-dependent perturbation theory is employed for treating the interaction of the active electron with the light target, and exact relativistic Coulomb-Dirac wave functions are used for the description of electronic states in the strong field of the projectile nucleus. The energy dependence of transition probabilities and partial cross sections is studied up to extreme relativistic energies of hundreds of GeV/u and beyond. An analytic representation of the asymptotic energy dependence of the projectile excitation cross section complements the numerically calculated impact-parameter-dependent probabilities and cross sections, providing additional insights.

The dependence of electron loss by 6-MeV/amu ${\mathrm{Xe}}^{18+}$ on target atomic number was investigated by measuring single-collision cross sections for loss of one to eight electrons in targets of the noble gases He, Ne, Ar, Kr, and Xe. The total-electron-loss cross sections were found to increase linearly with target atomic number, but an abrupt slope change was observed to occur between Ne and Kr. Calculated total-loss cross sections obtained using the n-body classical trajectory Monte Carlo method were in good agreement with the measurements. The dependence of the individual cross sections on the number of electrons lost was reasonably well represented by a semiempirical fitting procedure utilizing the independent-electron approximation. Additional measurements performed with a variety of molecular targets provided a rigorous test of cross-section additivity. It was found that the additivity rule works well in this collision regime and that the molecular nature of the target has remarkably little influence on the cross sections.

We experimentally demonstrate a method for selecting small regions of phase space for kicked rotor quantum chaos experiments with cold atoms. Our technique uses quantum accelerator modes to selectively accelerate atomic wave packets with localized spatial and momentum distributions. The potential used to create the accelerator mode and subsequently realize the kicked rotor system is formed by a set of off-resonant standing-wave light pulses. We also propose a method for testing whether a selected region of phase space exhibits chaotic or regular behavior using a Ramsey type separated field experiment.

We analyze the mean-field equilibrium states of a homogeneous Bose-Einstein condensate of boson particles in different internal states, possibly in the presence of an internal Josephson interaction, and we describe the quantum fluctuations by constructing an explicit form of the Bogoliubov transformation that characterizes the quasiparticle excitations of the system. The derivation of the Bogoliubov transformation is based on a simple geometrical picture which leads to a convenient parametrization of the transformation. Our calculations of physical properties, such as depletions and phonon velocities, as well as our discussion of stability, indicate the sense and the extent to which the internal Josephson interaction controls the many-body physics of multicomponent phase coherent matter.

A ring-shaped array of Bose-Einstein condensed atomic gases can display circular currents if the relative phase of neighboring condensates becomes locked to certain values. It is shown that, irrespective of the mechanism responsible for generating these states, only a restricted set of currents are stable, depending on the number of condensates, on the interaction and tunneling energies, and on the total number of particles. Different instabilities due to quasiparticle excitations are characterized, and possible experimental setups for testing the stability prediction are also discussed.

We propose a scheme of storing and releasing pulses or cw beams of light in a moving atomic medium illuminated by two stationary and spatially separated control lasers. The method is based on electromagnetically induced transparency but in contrast to previous schemes, storage and retrieval of the probe pulse can be achieved at different locations and without switching off the control laser.

A relationship between the total wave function describing electron-impact ionization of hydrogen and the one representing scattering of two electrons and a proton in the continuum is revealed. On the basis of this relationship, forms of the scattered wave for the ionization process valid in all asymptotic domains are obtained. When all interparticle distances become large, the new wave functions reduce to the well-known Peterkop asymptotic wave function obtained in the hyperspherical approach. In particular, the Peterkop wave function is obtained by direct application of the present approach. This allows one to resolve the long-standing amplitude-phase ambiguity problem, which is an artifact of the hyperspherical approach to the ionization process. The Peterkop wave function is invalid when the two electrons are close to each other. This causes problems in practical calculations even in the domain where all particles are far apart. Our formulation provides a solution to this problem.

We show that the critical temperature of a one-dimensional gas confined by a power-law potential should be lower than that in the paper of Bagnato and Kleppner [Phys. Rev. A 44, 7439 (1991)]. Moreover, a sketch of the critical temperature is given in greater detail.