New results of infrared photoexcitation experiments on undoped ${\mathrm{La}}_2$Cu${\mathrm{O}}_4$ and ${\mathrm{Nd}}_2$Cu${\mathrm{O}}_4$ are reported. We observed two broad electronic excitations within the charge-transfer energy gap and an associated phonon bleaching, possibly originating from strong charge-lattice coupling. Our results are discussed in terms of the condensation of self-localized photocarriers in the Cu${\mathrm{O}}_2$ planes at low temperatures.

In a graded InAlGaAs superlattice grown by molecular-beam epitaxy at 500 °C, we have observed a novel steady-state photovoltaic effect which arises from an internal polarization field under above-band-gap (hν>${\mathit{E}}_{\mathit{g}}$) illumination. The saturation value is ∼0.1 V and the response time to the illumination is limited by the oscilloscope resolution to ∼2 ns. The observations are in quantitative agreement with a theoretical model by which we fit our data and extract a minority-carrier lifetime ${\mathrm{\tau }}_{\mathit{e}}$ of ∼30 ps. This effect is substantially reduced in a second wafer grown at 550 °C, in which ${\mathrm{\tau }}_{\mathit{e}}$ is expected to be long.

We study a rule for quantizing chaos based on the dynamical zeta function defined by a Euler product over the classical periodic orbits as suggested by Gutzwiller’s semiclassical trace formula. A test of our approximate quantization formula is carried out for the planar hyperbold billiard, which shows that at least the first 150 quantum energy levels can be generated.

Localization in the quantum-kicked-rotator problem leads to nontrivial dynamical correlations that are absent in the classical limit. Consequently, both coherence and diffusion in the presence of colored noise depend on its long-range autocorrelations. This implies that a Markovian treatment of the dynamics for a system that is coupled to a low-temperature heat bath is not valid even if the system is classically chaotic.

The close relations between statistical properties of quantum dissipative systems and scattering systems is discussed. It is conjectured that for quantum chaotic scattering the distribution of the resonance poles of the S matrix is generic and follows the predictions of the Ginibre ensemble of random non-Hermitian matrices. This phenomenon has been demosntrated on a simple example of a single particle scattered by eight randomly distributed point obstacles in three dimensions.

The chaotic dynamics found in the diode resonator has been converted into stable orbits with periods up to 23 drive cycles long. The method used is a modification of that of Ott, Grebogi, and Yorke [Phys. Rev. Lett. 64, 1196 (1990)]. In addition to stabilizing existing low-period orbits, the method allows making small alterations in the attractor permitting previously nonexistent periodic orbits to be stabilized. It is an analog technique and therefore can be very fast, making it applicable to a wide variety of systems.

The demonstrations of Wigner and others, that observables which do not commute with additive conserved quantities cannot be measured precisely, are reexamined. A proposed new formulation of the claim is shown to be valid for observables with a continuous spectrum whenever the conserved quantities are bounded. However, a countermodel is constructed, and it suggests that the position can be measured as precisely as the momentum even though the measuring interaction conserves the total linear momentum.

We propose a new model for studying dissipation in quantum-mechanical systems. The mechanism of dissipation is solely due to the scattering of the environment excitations by the particle of interest. We treat the problem via the functional integral formalism. It is shown that the model gives a damping parameter which is temperature dependent.

The asymptotic spectrum of the wave-height autocorrelation is of power-law form for surface gravity waves in deep water. Physical oceanographers have utilized Kolmogorov-type scaling arguments within transport theory in order to predict the exponent of the power law once the wave statistics become stationary. I advance the hypothesis that the asymptotics can be achieved using Hamilton’s equations correct to third order with an arbitrary nonsingular interaction term which has the symmetry, degree of homogeneity, and quasilocality in k space of the full Hasselmann interaction term. Examples which support the hypothesis are presented, and its further implications are discussed.

A theorem which describes the Newtonian dynamics of the center of mass (as defined with respect to the energy density) of nonlinear Klein-Gordon-type solitary waves is proved. It appears as a generalization of Ehrenfest’s theorem in quantum mechanics, which describes the Newtonian dynamics of the center of mass (as defined with respect to the probability density) of the linear wave functions. As an example, the interaction of recently discovered two-dimensional pulsons [cf. E. M. Maslov, Phys. Lett. A 151, 47 (1990)] is considered.

Spin-1/2 xxz and q-Potts quantum chains with translation-invariant boundary conditions are analyzed as representations of the periodic Temperley-Lieb-Jones algebra. A connection with the affine Hecke algebra is established and used to find the irreducible content. This analysis provides an explanation for both the degeneracies and the overlap in the spectra of these models.

A black hole can carry quantum numbers that are not associated with massless gauge fields, contrary to the spirit of the ‘‘no-hair’’ theorems. In the Higgs phase of a gauge theory, electric charge on a black hole generates a nonzero electric field outside the event horizon. This field is nonperturbative in ħ and is exponentially screened far from the hole. It arises from the cloud of virtual cosmic strings that surround the black hole. In the confinement phase, a magnetic charge on a black hole generates a classical field that is screened at long range by nonperturbative effects. Despite the sharp difference in their formal descriptions, the electric and magnetic cases are closely similar physically.

An on-shell unstable particle produced in a tree-level process, such as W in t→qW, induces a CP violating signal through its width. This effect arises from an Im(tree)×Re(loop) type of interference. Among t→qq’q¯ processes (e.g., t→bcb¯) proceeding either through the tree-level t→qW or the one-loop t→q’+(virtual g) reactions, the CP asymmetry is largest for the case t→dcd¯ and is of scrO(η/${\lambda }^2$) in Wolfenstein’s parametrization. The resulting effects are found to be small in the standard model, but are much larger than those obtained for radiative top-quark decays. We also briefly discuss B decays where such a mechanism may cause CP violation in, for example, b→${\mathit{se}}^{+}$${\mathit{e}}^{\mathrm{-}}$.

Coincidence measurements of (p,n) reactions at 1.5 GeV/c in the Δ excitation region have been carried out for the first time. The location of the Δ peak in the neutron spectrum is found to be dependent on the coincident particles. The peak in coincidence with p${\mathrm{\pi }}^{+}$ is shifted to lower momenta compared to the free case, in contrast to the inclusive spectrum and the coincidence with other particles where it is shifted to higher momenta. The p${\mathrm{\pi }}^{+}$ invariant-mass distribution for C is significantly lower and broader than that for H. The coincidence data set stringent constraints on theoretical models introduced to interpret the peak shift in inclusive spectra.

Delayed ionization with average lifetimes on the order of several μsec has been observed for two-photon 308-mn excimer laser ionization of ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$.

We report the observation of spin echoes resulting from the time reversal of isotropic many-body spin couplings in zero-field NMR. The coherent-averaging pulse sequences responsible for the scaling and the time reversal of isotropic interactions of first and second rank are based on cubic and icosahedral symmetry.

The 3γ decay of spin-aligned triplet positronium (Ps) is used for a test of CP invariance (charge conjugation and parity). This is the first use of the Ps atom to investigate the CP symmetry. The angular correlation (S^⋅k${\mathrm{^}}_1$)(S^⋅k${\mathrm{^}}_1$×k${\mathrm{^}}_2$) was measured, where S is the Ps spin and ‖${\mathbf{k}}_1$‖>‖${\mathbf{k}}_2$‖>‖${\mathbf{k}}_3$‖ are the γ momenta. If this correlation has a nonzero amplitude, CP is not conserved. No amplitude was found at the 1.5% level of uncertainty.

We demonstrate optical techniques for precisely measuring the position of moving atoms. Micron spatial resolution is attained by the methods which ultimately will scale to yield nanometer resolution limited by the uncertainty principle.

Coherences between atomic substates are driven by a resonant interaction with light and transferred between individual sublevel transitions. We present an experimental scheme, based on two-dimensional Fourier-transform spectroscopy, that allows direct observation of this coherence transfer.

Using an acoustic technique profile analysis we have studied the growth of viscous fingers inside 3D porous media. The experimental data support the definition of an instability parameter which captures the essential features of the viscous fingering; its dependence on the viscosity ratio, on the flow rate, and on the nature of the porous medium is compared to available theory. Our data demonstrate the predicted crossover between diffusive and linear growth and the growth enhancement due to coupling between large viscosity ratio and velocity-dependent hydrodynamic dispersion.