We present a quantum theory of feedback in which the homodyne photocurrent alters the dynamics of the source cavity. To the nonlinear stochastic (Ito) evolution of the conditioned system state we add a feedback term linear in the instantaneous stochastic (Stratonovich) photocurrent. Averaging over the photocurrent gives a feedbackk master equation which has the desired driftlike term, plus a diffusionlike term. We apply the model to phase locking a regularly pumped laser, and show that under ideal conditions the noise spectra of the output light exhibit perfect squeezing on resonance.

We show that electromagnetically induced transparency in a dense media is not a Beer’s law superposition of the single atom response. When an arbitrarily shaped pulse is applied to an ensemble of population-trapped atoms, the atoms will generate a matching pulse shape on the complementary transition and, after a characteristic distance, render themselves transparent.

We propose a scheme for preparing coherent squeezed states of motion in an ion trap based on the multichromatic excitation of a trapped ion by standing- and traveling-wave light fields. The squeezed state is produced when the beat frequency between two standing-wave light fields is equal to twice the trap frequency, and is indicated by a ‘‘dark resonance’’ in the fluorescence emitted by the ion.

We have studied the deflection of ground-state sodium atoms passing through a micron-sized parallel-plate cavity by measuring the intensity of a sodium atomic beam transmitted through the cavity as a function of cavity plate separation. This experiment provides clear evidence for the existence of the Casimir-Polder force, which is due to modification of the ground-state Lamb shift in the confined space of a cavity. Our results confirm the magnitude of the force and the distance dependence predicted by quantum electrodynamics.

The understand the role of nonlinear dispersion in pattern formation, we introduce and study Korteweg–de Vries–like equations wtih nonlinear dispersion: ${\mathit{u}}_{\mathit{t}}$+(${\mathit{u}}^{\mathit{m}}$${)}_{\mathit{x}}$+(${\mathit{u}}^{\mathit{n}}$${)}_{\mathit{x}\mathit{x}\mathit{x}}$=0, m,n>1. The solitary wave solutions of these equations have remarkable properties: They collide elastically, but unlike the Korteweg–de Vries (m=2, n=1) solitons, they have compact support. When two ‘‘compactons’’ collide, the interaction site is marked by the birth of low-amplitude compacton-anticompacton pairs. These equations seem to have only a finite number of local conservation laws. Nevertheless, the behavior and the stability of these compactons is very similar to that observed in completely integrable systems.

The quantum density of states of the Hénon-Heiles Hamiltonian exhibits prominent low-frequency beats as a function of energy. We interpret the beats in terms of interferences of the three simplest isolated classical periodic orbits by a calculation of their amplitudes in the Gutzwiller trace formula. We show that periodic orbit theory can reproduce classically the main characteristics of the quantum beats. Both stable and unstable orbits contribute substantially in generating these long-range correlations, which coexist with the short-range fluctuations giving nearest-neighbor spacings distributions typical for chaos. With a Fourier analysis our conclusions confirm the quantum spectrum.

The signature of chaos in the spectral autocorrelation function and in its Fourier transform, the survival probability, is shown to be in good agreement with the predictions of random matrix theory. An expression is proposed for the survival probability of an experimentally prepared nonstationary state when the dynamics are intermediate between chaotic and regular. Its validity is tested through the study of a model Hamiltonian . Two parameters can be extracted from the above observable, one which characterizes the level statistics and one which characterizes the distribution of transition intensities.

Stochastic resonance is a phenomenon seen in multistable systems where the addition of noise to the system can amplify small periodic signals. We show in an experiment with a circuit that many of the concepts used to describe crises may also be used to describe stochastic resonance. We speculate that stochastic resonance may be an example of a crisis. This would allow the use of dynamical concepts to describe a process that is usually considered statistically.

A quantitative measure of determinism in a recurrent time series is developed. Specifically, scalar time series data are used to form a vector series in reconstructed phase space. A statistic is then developed to measure the observed ‘‘continuity’’ of the vector series. The statistic is used as a measure of determinism. Several examples are included to demonstrate the effectiveness of the method.

Laser-induced fluorescence imaging of a shock-accelerated thin gas layer, produced by a planar ${\mathrm{SF}}_6$ jet in air, shows multiple flow evolutions. Richtmyer-Meshkov instability causes spatially periodic perturbations initially imposed on the jet to develop into one of three distinct flow patterns, indicating nonlinear instability growth. Slight differences in the vorticity distribution deposited on the air-${\mathrm{SF}}_6$ interfaces by the shock interaction produce a bifurcated flow, observed as mushroom-shaped or sinuous-shaped interfacial patterns.

We consider the unfolded spectra of disordered systems with the topology of a ring, in the presence of an Aharonov-Bohm flux. We study the flux dependence of a single energy level. We find that the correlator of the derivatives at two different fluxes has a universal functional form, and propose that the result is valid for all systems with Wigner-Dyson statistics.

The synchroton motion of a beam was tracked for the first time by digitizing the phase of the beam signal from a high bandwidth wall gap monitor relative to the rf phase and the momentum deviation with a transverse beam position measurement in a high dispersion region. The measured synchrotron tune as a function of the synchrotron amplitude agrees well with theory. When the rf stable phase angle was modulated harmonically, the response of the synchrotron motion showed characteristics of chaos and bifurcations of a parametric resonant system. Manipulating the rf system to create islands in the synchrotron phase space may offer applications in future hadron colliders.

We have measured and calculated the intensity profiles for S 2p photoemission at 1327 eV from the well-defined adsorbate system, c(2×2)S on Ni(001), and have analyzed these via several holographic imaging procedures. Images of nearest-neighbor S atoms are clearly seen in both experiment and theory, and their positions are improved if effects due to twin images are suppressed by analyzing only a half hologram. Image positions are further improved to within ±0.2–0.3 Å with corrections for scattered-wave amplitudes and phase shifts.

We have imaged Cu atoms near a (100) single-crystal face using photoelectron holography and have applied for the first time a multiple-wave-number method for improving the quality of images obtained from experimental results. When compared to images obtained from single-energy holograms, the structural information extracted from the multiple-wave-number, phased-sum method gives substantial resolution improvement, twin-image suppression, and artifact reduction.

Parameter-free first-principles phonon calculations are used in conjunction with multiple-scattering electron-energy-loss calculations to reveal new localized modes on Cu(111) and Ag(111). The discovery of these z-polarized localized modes along Γ¯ M¯ and Γ¯ K¯ provides for the first time good agreement between theory and all the existing helium-atom-scattering and electron-energy-loss experimental results. The new results indicate that it is not necessary to evoke exotic models such as anomalous surface dynamical effects on these densely packed surfaces.

Scanning tunneling microscopy study of monolayers of the chiral-liquid-crystal-forming molecule W7 shows the coexistence of two phases having unit cells of opposite chiral symmetry, one a 2D crystalline phase and the other a 1D stacking-disorder phase exhibiting the kind of structural ambivalence characteristic of bulk liquid crystals. The interrow interactions in the stacking-disorder phase can be described using a one-dimensional three-state Potts model with extended interrow interactions.

The structural and electronic properties of amorphous carbon are studied with tight-binding molecular-dynamics simulations. An amorphous carbon structure with 216 atoms obtained from our simulation gives a structure factor S(Q) in very good agreement with the results of neutron scattering from a sputtered a-C sample. We found that the amorphous structure consists of graphitelike fragments embedded in a matrix of both twofold and fourfold coordinated atoms. We also found a small pseudogap in the electronic density of states at the Fermi level.

We report a first-principles calculation of impurity effects on adhesion. C, O, B, and S impurities all cause a pronounced decrease in the adhesive energies of the Mo/${\mathrm{MoSi}}_2$(001) heterophase interface. S decreases the peak interfacial strength, while C, O, and B increase it. All impurities increase interfacial spacing in proportion to their covalent radii. Impurity mechanisms are identified.

Scaling density profiles O(N) symmetric systems confined between two parallel plates with a large separation L are analyzed by field-theoretical methods for a continuous phase transition at bulk criticality ${\mathit{T}}_{\mathit{c},}$b in spatial dimension d=4-ɛ. At distances z≪L from one wall a the profile contains a perturbation ${\mathit{B}}_{\mathit{a},}$b(z/L${)}^{\mathit{d}}$ induced by the distant wall b. In contrast to previous expectations the ratio of the universal amplitude ${\mathit{B}}_{\mathit{a},}$b and the corresponding Casimir amplitude is not hyperuniversal, i.e., not independent of both surface universality classes characterizing the walls a and b.

Brownian dynamics simulations were used to study the adhesion of hard spheres on a solid surface by taking the hydrodynamic interactions into account. Special attention was paid to analyze the configuration of the assembly of adsorbed particles. These results were compared to configurations generated by the extensively studied random sequential adsorption (RSA) model. In our case the adsorption probability for a particle is almost uniform over the entire available surfae. This surprising result shows that RSA provides a good approximation to generate adsorbed particle configurations.