The Einstein-Podolsky-Rosen paradox is demonstrated experimentally for dynamical variables having a continuous spectrum. As opposed to previous work with discrete spin or polarization variables, the continuous optical amplitudes of a signal beam are inferred in turn from those of a spatially separated but strongly correlated idler beam generated by nondegenerate parametric amplification. The uncertainty product for the variances of these inferences is observed to be 0.70±0.01, which is below the limit of unity required for the demonstration of the paradox.

According to the de Broglie pilot wave theory, a pilot wave which is empty of photons is still capable of physical effects like induced coherence. We have carried out an experiment to test this prediction. The experiment involves interference of photons produced by down-conversion in two nonlinear crystals and depends on the mutual coherence induced between the two signal beams by an idler. When the photon is removed from the idler by a beam splitter, it is found that the resulting ‘‘empty pilot wave’’ no longer induces coherence. This violates at least the Selleri-Croca version of the de Broglie pilot wave theory makes the physical reality of the corresponding pilot wave doubtful.

The stochastic Landau equation for a periodically driven process with either two discretely degenerate attractors or a continuum of degenerate attractors is studied for small noise. We calculate analytically the probability ${\mathit{P}}^{\mathrm{tr}}$ for the transition between the attractors leading to phase diffusion in the continuous case. Our results are in good agreement with numerical simulations and in the discrete case also with experiments on periodically driven Rayleigh-Bénard convection. They explain the sensitive dependence of ${\mathit{P}}^{\mathrm{tr}}$ on the equation’s parameters.

It is proposed that the dimension D be used as a perturbation parameter. The coefficients in the resulting dimensional expansion, a series in powers of D, can be obtained in both quantum-mechanical and field-theoretic models. In this paper the first three terms in the dimensional expansion for the ground-state energy density for a self-interacting ${\mathrm{\phi }}^{2\mathit{K}}$ field theory are calculated. Dimensional expansions are shown to provide accurate nonperturbative analytic results.

We calculate corrections to the masses of the two CP-even Higgs bosons in the minimal supersymmetric model. We find an upper bound for the mass of the lighter Higgs scalar, and a lower bound for the mass of the heavier Higgs scalar. In our analysis we consider all possible variations of superparticle masses between 0.1 and 1 TeV. By requiring the light Higgs boson to be greater than the current experimental bound we rule out a region of the tanβ–top-mass parameter space, where tan β is the ratio of vacuum expectation values of the two Higgs fields. We make our formalism explicit to elucidate the treatment of mass thresholds.

Green’s-function Monte Carlo methods are used to determine the Euclidean proton response of light nuclei from a realistic Hamiltonian containing two- and three-nucleon potential models. Final-state interactions are exactly included in this approach. The calculated Euclidean proton response functions for the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ nucleus are found to be in excellent agreement with those obtained from an analysis of the longitudinal response functions measured in (e,e’) experiments at the Bates and Saclay laboratories.

Calculations of collision-induced absorption spectral moments ${\gamma }_1$ and ${\mathrm{\alpha }}_1$ for ${\mathrm{N}}_2$ and ${\mathrm{CO}}_2$ molecular pairs are presented which, for the first time, fully account for the anisotropic components of the intermolecular potentials. The results of these rigorous computations, performed at selected temperatures, are compared with approximations based on the perturbative approach and the infinite-order sudden approximation. In this way both important aspects of the effects of an anisotropic interaction and the ability of these two approximations to take them into account are demonstrated.

The positronium-formation cross section was measured for positron collisions with atomic hydrogen in a crossed-beam experiment. Measurements were made in the energy range of 13 eV≤E≤205 eV. At E=15±2.8 eV we observed a maximum cross section of (4.3±0.8)×${10}^{\mathrm{-}16}$ ${\mathrm{cm}}^2$; because of averaging over an energy-resolution function of 6.5 eV FWHM, the observed maximum is a lower limit of the true maximum. For E≥75 eV the cross section is zero within our error margin of 0.3×${10}^{\mathrm{-}16}$ ${\mathrm{cm}}^2$. No other measurements but numerous theoretical predictions are available for comparison.

The nonretarded van der Waals coefficients ${\mathit{C}}_6$ and ${\mathit{C}}_8$ are determined for all pairs of neutral sodium microclusters with 1, 2, 8, 20, and 40 atoms. These small systems are described self-consistently within the jellium model and their multipole dynamical polarizabilities calculated making use of the time-dependent local density approximation. It is found that quantum size effects, in particular Landau fragmentation, play a crucial role in the determination of these coefficients. Furthermore, it is found that the van der Waals coefficients are very insensitive to the internal temperature of the clusters, in the range of temperatures presently reachable experimentally. A brief discussion on the accuracy of the predicted values is carried out.

We have calculated the effect of material absorption on the rate of spontaneous emission by an embedded atom using a macroscopic Green-function approach and a microscopic Hamiltonian method that includes reservoir damping. When local field effects are neglected, the free-space emission rate is modified by the real part of the refractive index at the transition frequency of the embedded atom. Local field effects are introduced via a local field correction factor. This modification of the spontaneous emission rate generalizes a well-known result for transparent media and is of crucial importance in assessing the degree of inhibition of spontaneous emission for frequencies close to the resonances of the dielectric.

We show theoretically and experimentally that an infinitesimal imperfection in the symmetry of a system has a macroscopic influence on the stability of spatiotemporal patterns originated in a symmetry breaking process. This result makes it possible to discuss differences between experiments and models in which such corrections have not been taken into account. We show that the stability of the solutions arising from the first symmetry breaking transition in the Maxwell-Bloch equations is valid for every laser with radial symmetry.

A very intense electron plasma wave is resonantly excited at the top of a broad, flat density profile, by a longitudinal very-high-frequency electric field oscillating at the plasma frequency. Electric field energy densities W=Ẽ ${}_{}{}^2{}_{}{}^{}$/4π${\mathit{n}}_{\mathit{c}}$${\mathit{T}}_{\mathit{e}}$>${10}^3$ are produced, along with copious electrons and ions of kinetic energy K>${10}^3$${\mathit{T}}_{\mathit{e}}$. Reconstruction of the wave, from detailed measurements of electric field amplitude and phase, demonstrates wave breaking and accounts for the observed energetic particles.

The modulational instability of the high-phase-velocity plasma wave generated by a Nd-laser beat wave has been observed for the first time. Both ion and electron waves are detected when the electron density is close to the resonant density for which the plasma frequency is equal to the difference frequency between the two pump lasers. We also detect the presence of harmonics of the beat frequency which are a signature of high-amplitude density perturbations.

The microscopic nature of defects in ion-implanted amorphous Si has been probed using Mössbauer spectroscopy. Analysis of the ${}_{}{}^{119}{}_{}{}^{}\mathrm{Sn}$ Mössbauer spectra obtained from ${}_{}{}^{119}{}_{}{}^{}\mathrm{Sb}$ in amorphous Si requires two independent sites for Sb in amorphous Si. Direct comparison of the isomer shifts and Debye temperatures of these lines with data from crystal Si demonstrates that the sites are a substitutional network site and an Sb-vacancy complex. The data suggest that point defects analogous to the crystal vacancy exist in the amorphous Si structure.

The quantum-deformed (1+1) Poincaré algebra is shown to be the kinematical symmetry of the harmonic chain, whose spacing is given by the deformation parameter. Phonons with their symmetries as well as multiphonon processes are derived from the quantum group structure. Inhomogeneous quantum groups are thus proposed as kinematical invariances of discrete systems.

We study the eleasticity of tethered, crystalline membranes in an applied in-plane electric field. The field lowers the critical dimension for the onset of anomalous elasticity from 4 to 5/2, allowing stringent experimental tests of the predictions of the renormalization group to be made. Two-in-plane elastic constants vanish at small wave vectors q like ${\mathit{q}}_{\mathrm{\perp }}^{\mathrm{\eta }}$, while the membrane bend modulus κ diverges like ${\mathit{q}}^{\mathrm{-}\mathrm{\eta }}$, with ${\mathrm{\eta }}_{\mathrm{\perp }}$+1/2(5-D)η=5-2D, exactly. The 5/2-ɛ expansion predicts η=0.27±0.03 and ${\mathrm{\eta }}_{\mathrm{\perp }}$=0.60±0.05 in D=2. We discuss several experiments to measure these exponents.

Parametric excitation yields new results, which cannot be obtained by conventional linear spectroscopy, on the collective modes in superfluid ${}_{}{}^3{}_{}{}^{}\mathit{B}$. In our ultrasonic experiments, performed in a chamber with four quartz crystals, we have excited the real squashing (J=$2^{+}$) modes by two simultaneous sound waves which are mutually either parallel, orthogonal, or antiparallel. Qualitatively these results are in agreement with the theoretical dispersion relation of the J=$2^{+}$ modes, and quantitatively we have been able to extract the collective-mode velocities from the line splittings in zero magnetic field.

A three-dimensional Toom model is defined and the properties of the interface separating the two stable phases are investigated. Using symmetry arguments we show that in the zero-noise limit the model has only nonequilibrium fluctuations and that the scaling is described by the anisotropic Kardar-Parisi-Zhang equation. The scaling exponents are determined numerically and good agreement with the theoretical predictions is found.

The origin of strain-induced, modulated domain structures observed in epitaxial ferroelectric lead titanate thin films is discussed using a phenomenological total-energy calculation. Linear elasticity is used to account for the substrate contribution while a free-energy functional of the Landau-Ginzburg-Devonshire type is used to calculate the domain-wall and the polarization contributions from the film. Good agreement between the predictions of this model and the experimental results is found for thickness-dependent properties such as the relative domain population and spontaneous strain.

A new mechanism is introduced to describe desorption from surfaces under conditions of strong electronic excitation. When repetitive excitations occur within the relaxation time for the adsorbate-surface vibration, the process of desorption induced by multiple electronic transitions may provide an enhancement of orders of magnitude over a single-excitation mechanism. This generalization of the classic Menzel-Gomer-Redhead picture encompasses within one formalism both single-excitation processes and a thermal limit. The mechanism may be operative in desorption by femtosecond laser pulses.