Based on a numerical representation of available experimental results, we analyze recent proposals in the sense that quantum vacuum radiation explains sonoluminescence. A comparison with purely classical dipole radiation emitted coherently is made. In both cases the effects arising only from the bubble surface dynamics cannot account for the observed emitted radiation.

It is shown that a suitable optical feedback loop contributes to focus the atoms passing through a standing wave within a cavity, thus improving the possibility of its localization.

We consider a variant of the Jaynes-Cummings model (JCM) which describes the interaction of a moving two-level atom with a single-mode electromagnetic field. The coupling of the moving dipole with the magnetic field which leads to the Roentgen interaction is taken into account. A solution in the dressed state description is presented in the spirit of the JCM.

We show that the Stark and Kerr Hamiltonians are deeply connected in the framework of dynamical algebras. We found that the algebras for both Hamiltonians are the same when physically relevant magnitudes, such as the population inversion and the $n$th order coherence function are considered as elements of a Lie algebra under commutation with the Hamiltonians. By analyzing the equations of motion we were able to find a set of conditions for the characteristic magnitudes of both Hamiltonians that leads to the same dynamical behavior for all the elements of the group. Finally, we conclude that the results of this paper can be generalized to any extension of the Jaynes-Cummings model, where any of the different elements of the group are present.

We extend the Wigner function formalism for parametric down-conversion experiments presented in a previous paper [Phys. Rev. A 55 3879 (1997)] to experiments involving propagation through a dispersive medium [Steinberg et al., Phys. Rev. A 45, 6659 (1992)], and polarization [Kwiat et al., Phys. Rev. A 45, 7729 (1992)].

I reply to the Comment [A. Mostafazadeh, Phys. Rev. A 55, 4640 (1997)] on my paper in Phys. Rev. A 53, 2053 (1996). In particular, there is nothing in the Comment except the final paragraph, which points out my two sick sentences in English. I give a simple example to explain my original meaning of the two sick English sentences and try to correct them.

We investigate the possibility of generating quantum macroscopic coherence phenomena by means of relativistic effects on a trapped electron.

A sequence of Bell inequalities for $N$-particle systems, which involve three settings of each of the local measuring apparatuses, is derived. For Greenberger-Horne-Zellinger states, quantum mechanics violates these inequalities by factors exponentially growing with $N$. The threshold visibilities of the multiparticle sinusoidal interference fringes, for which local realistic theories are ruled out, decrease as ${\mathrm{}(2/3)\mathrm{}}^N$.

We present a mathematically rigorous method suitable for bound-state and scattering process calculations for various three-atomic or molecular systems where the underlying forces are of a hard-core nature. We employed this method to calculate the binding energies and the ultra-low-energy scattering phase shifts below as well as above the breakup threshold for the three-He-atom system. The method has proved to be highly successful and suitable for solving the three-body bound-state and scattering problem in configuration space and thus it paves the way to study various three-atomic systems, and to calculate important quantities such as the cross sections, recombination rates, etc.

An azimuthal dependence for 1-keV electrons scattered elastically at a fixed polar angle from a beam of free, spatially oriented ${\mathrm{CH}}_3\mathrm{Cl}$ molecules prepared by an electrostatic hexapole technique was observed. Pronounced azimuthal distributions with orientation-dependent contributions of several percent were measured, demonstrating that for preferentially perpendicular orientation of the molecules with respect to the electron beam the diffraction pattern is no longer cylindrically symmetrical and reflects directly the orientation and alignment of the scattering state ensemble. The data are compared with model calculations using the independent-atom model and hexapole transmission calculations of the focused rotational state mixtures, taking both the linear and the quadratic Stark effect into account. Inclusion of the second-order Stark effect changes the calculated azimuthal distributions significantly and improves the agreement between experiment and theory.

We present convergent close-coupling calculations of electron scattering on H-like ions within the framework of the $S$-wave model. The onset of $Z^4$ scaling is demonstrated. In addition, elimination of pseudoresonances in the singlet channel is studied via variation of the exponential parameter in the Laguerre basis. The absence of pseudoresonances in the triplet channel is explained by reference to single-differential ionization cross sections. These considerations have application to recently developed $R$-matrix with pseudostates techniques.

We have applied the $R$ matrix with pseudostates (RMPS) method to calculate single and double ionization of helium by photon impact. Using the velocity gauge of the dipole operator, excellent agreement with high-precision experimental data is obtained for photon energies between threshold and 200 eV. While some discrepancies remain between results from different gauges, we demonstrate that the RMPS method can produce satisfactory results if either the length, velocity, or acceleration form of the dipole operator is used.

The loss of kinetic energy of highly charged, heavy ions (${\mathrm{Ar}}^{18+},$ ${\mathrm{Xe}}^{44+},$ and ${\mathrm{Au}}^{69+}$) in thin carbon foils has been measured as a function projectile velocity in the range from $6\times {10}^5$ to $11\times {10}^5\mathrm{m}/\mathrm{s}.$ Evidence for strong pre-equilibrium energy-loss enhancements is observed for highly charged xenon and gold ions.

Using the basis of Wannier states, we study the local dynamics of polarization gradient cooling for an atom driven on a $J_g=2\mathrm{}\to J_e=3\mathrm{}$ transition by a one-dimensional optical lattice. This analysis allows us to formulate a physical picture of the cooling mechanism, analogous to Sisyphus cooling for a $J_g=1/2\mathrm{}\to J_e=3/2\mathrm{}$ atom, which depends strongly on coherences in the Zeeman sublevels of the ground state. In addition, we are able to explain the steady-state properties of the laser-cooled atoms in a regime where the standard semiclassical analysis breaks down.

In a simple nonlinear optical system consisting of a sodium vapor cell and a single feedback mirror, the spatial and polarization degrees of freedom are simultaneously unstable if the incident light is nearly linearly polarized. The instability results in the formation of spatially separated domains of opposite elliptical polarization. For initially linearly polarized light, we find square patterns that give way to positive or negative hexagons if the polarization is elliptical. This confirms a recent theoretical prediction based on a purely dispersive model [Scroggie and Firth, Phys. Rev. A 53, 2752 (1996)]. However, absorption has to be accounted for to reproduce the experimentally observed threshold behavior.

We study the transient decay and rotation of a singly charged optical vortex in media with a photorefractive nonlinearity under conditions where the light intensity is high compared to the saturation intensity. Transient decay of an initially circular vortex is characterized by charge-dependent rotation, and stretching of the vortex along the direction of the photogalvanic or externally applied field. When the medium reaches a steady state the effective nonlinearity at large times disappears and the vortex returns to its initial shape.

The usual configuration of the Brillouin fiber ring laser is slightly modified to investigate the influence of polarization effects on the system dynamics. Experiments reveal behaviors that drastically contrast with those observed when the polarization of the light remains linear. The Stokes emission may exhibit periodic and quasiperiodic instabilities with an antiphase phenomenon involving two polarization eigendirections. The frequency detuning between the Stokes wave and the cavity resonances seems to play a key role in the system dynamics.

Traditional quantum error correction involves the redundant encoding of $k$ quantum bits using $n$ quantum bits to allow the detection and correction of any $t$ bit error. The smallest general $t=1\mathrm{}$ code requires $n=5\mathrm{}$ for $k=1\mathrm{}$. However, the dominant error process in a physical system is often well known, thus inviting the following question: Given a specific error model, can more efficient codes be devised? We demonstrate alternative codes that correct just amplitude damping errors that allow, for example, a $t=1\mathrm{}$, $k=1\mathrm{}$ code using effectively $n=4.6\mathrm{}$. Our scheme is based on using bosonic states of photons in a finite number of optical modes. We present necessary and sufficient conditions for the codes and describe construction algorithms, physical implementation, and performance bounds.

For a magnetic dipole precessing in a magnetic field, it is shown that the quantum dynamical vector field does not determine the commutation relations for the observables. Several nonlinearly related observables with identical quantum dynamics are constructed explicitly.

Prevention of a quantum system’s time evolution by repetitive, frequent measurements of the system’s state has been called the quantum Zeno effect (or paradox). Here we investigate theoretically and numerically the effect of repeated measurements on the quantum dynamics of multilevel systems that exhibit the quantum localization of classical chaos. The analysis is based on the wave function and Schrödinger equation, without introduction of the density matrix. We show how the quantum Zeno effect in simple few-level systems can be recovered and understood by formal modeling the effect of measurement on the dynamics by randomizing the phases of the measured states. This analysis is extended to investigate the dynamics of multilevel systems driven by an intense external force and affected by frequent measurements. We show that frequent measurements of such quantum systems results in delocalization of the quantum suppression of classical chaos. This result is the opposite of the quantum Zeno effect. The phenomenon of delocalization of the quantum suppression and restoration of quasi-classical time evolution of these systems, owing to repetitive frequent measurements, can therefore be called the quantum anti-Zeno effect. From this analysis we furthermore conclude that frequently or continuously observable quasiclassical systems evolve basically in a classical manner.