It is shown that the recently observed $\Delta I=4\mathrm{}$ bifurcation seen in superdeformed nuclear bands is also occurring in rotational bands of diatomic molecules. In addition, signs of a $\Delta I=8\mathrm{}$ bifurcation, of the same order of magnitude as the $\Delta I=4\mathrm{}$ one, are observed both in superdeformed nuclear bands and rotational bands of diatomic molecules.

Evidence is presented for the occurrence of the $\mathrm{LS}$-forbidden $p^4\left({}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}\right)md{}_{}{}^2{}_{}{}^{}F_{}^e{}_{}{}^{}$ autoionization resonances in both Br and Cl by a measurement of the photoelectrons associated with the $J$-resolved ${}_{}{}^3{}_{}{}^{}P_{2,1,0}^{}{}_{}{}^{}$ final ionic states. Effects of spin-orbit coupling are delineated at the $J$-term level for both the ${}_{}{}^2{}_{}{}^{}F_{}^e{}_{}{}^{}$ and the ${}_{}{}^2{}_{}{}^{}S_{}^e{}_{}{}^{}$ resonances, and differences for these spin-orbit-induced pathways are highlighted.

A spectrometer has been designed and built for the study of electron-ion scattering. The angular distribution obtained with this instrument for the elastic scattering of electrons from ${\mathrm{Na}}^{+}$ ions at 10 eV is presented. The measurements clearly demonstrate interference effects, deviating markedly from the Rutherford formula, and are in good agreement with the results of phase-shift calculations based on semiempirical potentials.

The density-density correlation function determining off-resonance light scattering in weakly interacting Bose-condensed gases in a trapping potential is calculated in the Bogoliubov approximation. The evaluation of the necessary matrix elements is carried out for positive scattering length in the WKB approximation using the Thomas-Fermi approximation for the condensate.

We present a model to describe the dynamical evolution of the delocalized electrons in a simple metal cluster during and following the passage of a charged particle at intermediate energies. Assuming a mean-field approximation we solve the Vlasov equation by combining the test-particle method and the numerical resolution of the Poisson equation at each time step. This method allows one to use a large number of test particles and to obtain a reliable behavior of the one-body phase-space density over more than 20 fs. The rate and features of fast electron emission are predicted.

In the intense field (long-wavelength) limit, the oscillating motion of an electron wave packet leads to multiple passes by the scattering Coulomb center. The influence of the Coulomb focusing, in combination with multiple returns, focuses parts of the electron wave function, increasing the efficiency of such intense field processes as multiphoton double ionization. Our calculations show enhancement by more than an order of magnitude for multiphoton double ionization of He at 0.8 μm.

Intense femtosecond laser pulses are used to study the Coulomb explosion of C${\mathrm{O}}_2$ molecules via ${\mathrm{O}}^{Z^{\prime \prime }}+{\mathrm{C}}^{Z^{\prime }}+{\mathrm{O}}^{Z+}$ fragmentation channels. Large-amplitude bending and stretching motions around an average linear elongated structure are observed using atomic ion momenta correlations' peak shapes in comparison with Coulomb explosion calculations. Of special interest are the enhanced multielectronic ionization at large internuclear separations as predicted by recent theoretical models developed for diatomic molecules and the strong structural transition between the unperturbed geometry of the molecule and the exploding configuration in the intense laser field.

We have measured spatially dependent multiple ionization of xenon in an intense ultrashort pulse laser field. The ion yields for various charge states are dramatically different due to selecting specific locations within a Gaussian laser focus. The data show a clear enhancement of higher charge states and the double ion exceeds the single ion yield at certain locations. A model based on space-dependent volume scaling for different charge states is presented.

Another optical nonlinear effect is reported: the transient self-bending of a laser beam within a photorefractive crystal under an external electric field. It is based on the large drift length of the photoinduced carriers and is observed during a transient regime immediately after applying the light beam. Results of a numerical simulation are supported by an experimental demonstration of the effect in cubic ${\mathrm{Bi}}_{12}$Ti${\mathrm{O}}_{20}$ at $\lambda =633\mathrm{}$ nm.

The quantum dynamics of coherent optical pulses are studied using a nondiagonal coherent-state generalized $P$ representation including photon-phonon interactions. Photon-number squeezing of coherent quantum solitons using spectral filtering is theoretically predicted. It is shown that Raman noise does not significantly reduce photon-number squeezing produced by spectral filtering of 1-ps fundamental coherent quantum solitons in optical fibers. Coherent $Nsech$ pulses with $N>\mathrm{}1\mathrm{}$ can show a larger reduction in photon-number fluctuations even at room temperature. The reduction in quantum noise for $N>\mathrm{}1\mathrm{}$ is not restricted to photon number and an improvement of more than 3 dB is also found for the quadrature-phase squeezed soliton experiments using a fiber Sagnac interferometer at 77 K.

In entangled systems values cannot be assigned to all quantum-mechanical observables of individual members of the system independent of the measurement context of the whole system. While various cases are known where properties like spin, momentum, energy, etc. can be entangled, entanglement itself is usually considered to be an objective property of the system. We show that situations can arise where this is no longer the case, and where therefore entanglement itself becomes an entangled property. © 1996 The American Physical Society.

Following the strategy of showing specific quantum effects by means of the violation of a classical inequality, a pair of Bell-type inequalities is derived on the basis of certain additional assumptions, whose plausibility is discussed in detail. Such inequalities are violated by the quantum mechanical predictions for the interaction of a two-level Rydberg atom with a single mode sustained by a high-Q resonator. The experimental conditions required in order to show the existence of forbidden values, according to a hidden variables formalism, in a real experiment are analyzed for various initial field statistics. In particular, the revival dynamics expected for the interaction with a coherent field leads to classically forbidden values, which would indicate a purely quantum effect. © 1996 The American Physical Society.

We compute the semiclassical coherent-state propagator for a particle moving in a one-dimensional box. In this semiclassical approach complex trajectories are stationary paths of the propagator’s asymptotic expansion and play a fundamental role. A second semiclassical approximation is also introduced, which makes use of real trajectories only. An application to a seemingly simple system, the infinite well, is carried out completely for the diagonal elements, and a comparison is made among the three possible methods, those based on complex and real trajectories and the ‘‘exact case’’ that is determined by decomposing the propagator into its eigenstates. © 1996 The American Physical Society.

Despite the seminal connection between classical multiply periodic motion and Heisenberg matrix mechanics and the massive amount of work done on the associated problem of semiclassical Einstein-Brillouin-Keller (EBK) quantization of bound states, we show that there are, nevertheless, a number of previously unexploited aspects of this relationship that bear on the quantum-classical correspondence. In particular, we emphasize a quantum variational principle that implies the classical variational principle for invariant tori. We also expose the more indirect connection between commutation relations and quantization of action variables. In the special case of a one-dimensional system a different and succinct algebraic derivation of the WKB quantization rule for bound states is given. With the help of several standard models with one or two degrees of freedom, we then illustrate how the methods of Heisenberg matrix mechanics described in this paper may be used to obtain quantum solutions with a modest increase in effort compared to semiclassical calculations. We also describe and apply a method for obtaining leading quantum corrections to EBK results. Finally, we suggest several modified applications of EBK quantization. © 1996 The American Physical Society.

Information-theoretic aspects of quantum inseparability of mixed states are investigated in terms of the α entropy inequalities and teleportation fidelity. Inseparability of mixed states is defined and a complete characterization of the inseparable 2×2 systems with maximally disordered subsystems is presented within the Hilbert-Schmidt space formalism. A connection between teleportation and negative conditional α entropy is also emphasized. © 1996 The American Physical Society.

We analyze the possibility of copying (that is, cloning) arbitrary states of a quantum-mechanical spin-1/2 system. We show that there exists a ‘‘universal quantum-copying machine’’ (i.e., transformation) which approximately copies quantum-mechanical states such that the quality of its output does not depend on the input. We also examine a machine which combines a unitary transformation and a selective measurement to produce good copies of states in the neighborhood of a particular state. We discuss the problem of measurement of the output states. © 1996 The American Physical Society.

We present an improved calculation of higher-order corrections to the one-loop self-energy of 2P states in hydrogenlike systems with small nuclear charge Z. The method is based on a division of the integration with respect to the photon energy into a high- and a low-energy part. The high-energy part is calculated by an expansion of the electron propagator in powers of the Coulomb field. The low-energy part is simplified by the application of a Foldy-Wouthuysen transformation. This transformation leads to a clear separation of the leading contribution from the relativistic corrections and removes higher-order terms. The method is applied to the 2${\mathit{P}}_{1/2}$ and 2${\mathit{P}}_{3/2}$ states in atomic hydrogen. The results lead to theoretical values for the Lamb shifts and the fine-structure splitting. © 1996 The American Physical Society.

I develop methods for analyzing quantum error-correcting codes, and use these methods to construct an infinite class of codes saturating the quantum Hamming bound. These codes encode k=n-j-2 quantum bits (qubits) in n=$2^{\mathit{j}}$ qubits and correct t=1 error. © 1996 The American Physical Society.

We consider the transmission of classical information over a quantum channel. The channel is defined by an ‘‘alphabet’’ of quantum states, e.g., certain photon polarizations, together with a specified set of probabilities with which these states must be sent. If the receiver is restricted to making separate measurements on the received ‘‘letter’’ states, then the Kholevo theorem implies that the amount of information transmitted per letter cannot be greater than the von Neumann entropy H of the letter ensemble. In fact the actual amount of transmitted information will usually be significantly less than H. We show, however, that if the sender uses a block coding scheme consisting of a choice of code words that respects the a priori probabilities of the letter states, and the receiver distinguishes whole words rather than individual letters, then the information transmitted per letter can be made arbitrarily close to H and never exceeds H. This provides a precise information-theoretic interpretation of von Neumann entropy in quantum mechanics. We apply this result to ‘‘superdense’’ coding, and we consider its extension to noisy channels. © 1996 The American Physical Society.

Accurate momentum-space properties for the neon-atom isoelectronic sequence from ${\mathrm{F}}^{\mathrm{-}}$ through ${\mathrm{Ar}}^{8+}$ are calculated from highly accurate configuration-interaction wave functions that were constructed according to a density convergence criteria. These results should provide a benchmark to which calculations of momentum-space properties derived from other methods may be compared. Our results show that the inclusion of electron correlation has a smaller effect on these properties for the Ne sequence than on other isoelectronic sequences. The entropy sum is observed to increase with the inclusion of electron correlation which further substantiates the claim of its use as a measure of basis set or density quality. © 1996 The American Physical Society.