The phenomenon of tunneling is investigated for a symmetric double-well potential perturbed by a monochromatic driving force. The analysis is based on a numerical treatment of the quantum map that propagates the system over one period of the external force, and of the spectrum of its eigenphases (quasienergies). The variety in the quasienergy spectrum, such as exact and avoided crossings, leads to novel forms of coherent tunneling. In particular, for specific parameter values of the driving force, we find almost complete localization of the wave packet in one of the wells.

Experimental studies of amplification in a two-cavity X-band gyroklystron are reported. The system utilizes a thermionic magnetron injection gun at voltages up to 440 kV and currents up to 190 A in 1-μs pulses. Optimum performance is achieved by tapering the magnetic-field profile. Peak powers of 20 MW in the ${\mathrm{TE}}_{01}$ mode at 9.87 GHz are measured with calibrated crystals and with methanol calorimetry. Resultant efficiencies are in excess of 31% and large-signal gains surpass 26 dB. The experimental results are in good agreement with simulated results from a partially self-consistent, nonlinear, steady-state code.

The set of orientations of a measuring device (e.g., a Stern-Gerlach magnet) produced by the action of a Lie group constitutes a honmogeneous space S (e.g., a sphere). A hidden-variable measure determines a metric D on S, the triangle inequality being Bell’s inequality. But identification of S with Hilbert-space projectors induces a locally convex metric d on S. The Einstein-Podolsky-Rosen (EPR) hypotheses imply that D=${\mathit{d}}^2$, which is impossible because the square of a locally convex metric cannot be a metric. This proves the Bell-EPR theorem. Classical systems avoid the contradiction by allowing only values d=0,1. The ‘‘watchdog’’ effect is shown to result from the form of the quantum-mechanical metric.

It has been shown that two correlated photons incident upon two distant interferometers can give a coincidence counting rate that depends nonlocally on the sum of the phases of the two interferometers. It is shown here that the results of existing experiments violate a simple inequality that must be satisfied by any classical or semiclassical field theory. The inequality provides a graphic illustration of the lack of objective realism of the electric field.

We consider the statistical mechanics of an interacting anyon gas with a repulsive pair potential of the form g/${\mathit{r}}^2$. The second virial coefficient is calculated and shown to be a smooth function of the statistical parameter α for g>0, without the cusps previously found at the Bose point in a noninteracting anyon gas. As g→0 the cusps remain absent but a different type of singularity develops at the Bose point, showing that the order of limits is crucial.

We show that high-frequency, small-amplitude oscillations of Newton’s constant G can dramatically alter cosmology even if the frequency is very high compared to the expansion rate. For example, it is possible to have a spatially flat universe in which dynamical tests of Ω==(matter density)/(critical density)—tests which attempt to directly measure the mass density of the universe—obtain values less than unity (Ω==0.1–0.3, say). The cosmological effects can be obtained in a frequency-amplitude range allowed by all known constraints on G and its time derivative.

We present results for static hadronic correlation functions in the high-temperature phase of QCD with four flavors of dynamical quarks. We confirm chiral-symmetry restoration through the degeneracies of the spectrum of screening lengths. We also find that the screening lengths for the ρ and N channels at T≳1.2${\mathit{T}}_{\mathit{c}}$ are close to that in a free quark gas.

We propose a topological model for the confining-phase transition based on string formation. Our glueball is a string loop, our baryon a ssY-shaped junction. If ${\mathit{f}}_2$(1720) is a glueball, we estimate its production rate to be of order a few percent in the cc¯ system and ∼5% for inclusive decay of the bb¯ system. A numerical simulation shows that glueball and baryon production depend strongly on the shape of the parton shower. These shape dependences may prove useful as diagnostics for jetiness. If our model is correct, ${\mathrm{\chi }}_{\mathit{c}}$, ψ(2S), and Υ will be excellent sources for studying glueball spectroscopy.

We show how to calculate the root-mean-square parity-violating matrix element M for a heavy nucleons of valence nucleon number ${\mathit{A}}_{\mathit{v}}$ in terms of a standard parity-violating interaction ${\mathit{V}}^{\mathrm{PV}}$. For large values of ${\mathit{A}}_{\mathit{v}}$, we find a scaling law for M in terms of ${\mathit{A}}_{\mathit{v}}$ and the number of core nucleus. We compare our results to a recent measurement of M in ${}_{}{}^{239}{}_{}{}^{}\mathrm{U}$, obtaining results that bracket the data for three previously determined parameter sets of ${\mathit{V}}^{\mathrm{PV}}$.

Exact numerical calculations with Lagrange constraints are used to determine the lowest terms in an expansion for the two-Skyrmion interaction. The nucleon-nucleon potential which results after semiclassical quantization compares better with the phenomenological Paris potential than do previous calculations in the Skyrme model which used the product approximation. In particular, the present calculations show a sizable medium-range attraction in the central channel, a result that is not found with the product approximation.

Second-order interference is observed in the superposition of signal photons from two coherently pumped parametric down-converters, when the paths of the idler photons are aligned. The interference exhibits certain nonclassical features; it disappears when the idlers are misaligned or separated by a beam stop. The interpretation of this effect is discussed in terms of the intrinsic indistinguishability of the photon paths.

The results of a high-resolution x-ray-diffraction study of the smectic phases in mixtures of ${\mathrm{DB}}_7$OCN and 8OCB show that the incommensurate smectic-${\mathit{A}}_{\mathit{i}2}$ phase, previously reported in this mixture, is in fact a coexistence of the partially bilayer smectic-${\mathit{A}}_{\mathit{d}}$ and the bilayer smectic-${\mathit{A}}_2$ phases at a first-order phase transition between them.

For equilibrium systems with Ising symmetry, the three-point correlation function is always zero above criticality. When a lattice-gas version of this system is driven to a nonequilibrium steady state, this correlation becomes nontrivial. Its dominant large-scale behavior is found to be a consequence of both the manifest breaking of Ising symmetry by the driving force and the more subtle violation of the fluctuation-dissipation theorem.

A vibrating-wire technique has been used to directly measure the viscosity increase in a dilute ${}_{}{}^3{}_{}{}^{}\mathrm{-}_{}^4{}_{}{}^{}$He solution caused by brute-force spin polarization up to 40%. The viscosity of a solution with degeneracy temperature ${\mathit{T}}_{\mathit{F}}$=19.5 mK was measured over the temperature range 6.1–100 mK in magnetic fields of 1.00 and 7.96 T. Spin polarization caused a marked decrease in the mechanical Q of the viscometer at low temperatures. The observed viscosity is compared with calculations of the transport coefficients of dilute quantum gases for all temperatures and spin polarizations.

We present measurements of the slip of normal ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ contained between a pair of highly polished silicon plates mounted on a torsional oscillator. The resulting effective viscosity of pure normal ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ is not consistent with simple slip theory and shows characteristics previously observed only with a surface layer of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ present. We have also observed the onset of specularity induced by the addition of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. This onset occurs after 2 monolayers of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ have been completed and can be associated with superfluidity of the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$.

It is shown that electron tunneling from a very narrow tip should be effected, in an essential manner, by the quantum uncertainty in its transverse momentum induced by the confinement in the tip. This effect produces a strong asymmetry in the current-voltage characteristics of the tunnel junction, and to other unusual consequences. Different manifestations of the effect of the quantum uncertainty principle are analyzed.

Quantum transport in disordered systems can be studied via the transfer matrix M. In a previous paper, the statistical distribution of M at the mesoscopic level was constructed from single-scattering units. The assumption of ‘‘isotropy,’’ that restricted the model to certain observables for quasi-1D systems, is relaxed in this Letter. The new limiting distribution satisfies a diffusion equation, is universal, specified by the mean free paths between all pairs of channels, and is insensitive to other microscopic details. Results for the ballistic, metallic, and localized regimes are promising.

Echoes have been observed in an NMR experiment on isolated ${}_{}{}^{11}{}_{}{}^{}\mathrm{B}$ nuclei in a Si matrix which arise from a refocusing of the second-order quadrupolar interaction. The quadrupolar couplings are so large that only the central transition is excited. A theoretical treatment using fictitious spin-1/2 operators is presented which shows that the fictitious secular part of the interaction is responsible for the echo formation. The decay of the echo train is caused by the fictitious nonsecular terms.

We show for the first time that electron-energy-loss measurements of atomic absorption are different from the soft-x-ray photoyield data in the region influenced by the core exciton. We suggest that the core-exciton envelope function is influenced by the swift electron and its associated charge-density wake. Solving Schrödinger’s equation for a model transition potential including the swift electron, we find that the observed differences for ${\mathrm{SiO}}_{\mathit{x}}$, diamond, and Si can be reproduced. Spectra from aluminum are included as a comparison when the exciton is absent.

Studies of the formation of a nonmagnetic/magnetic silver/iron interface by spin-polarized photoemission identify magnetic interface states showing discrete binding energies dependent on the number of atomic layers in the overlayer. The results for one layer of silver on iron are in good agreement with a full-potential linearized-augmented-plane-wave calculation and tight-binding modeling allows us to reproduce qualitatively the layer-dependent binding energies for one, two, and three layers of silver on iron. The interface states appear to be related to a minority surface resonance on the iron surface.