We have measured doubly differential cross sections for slow electrons emitted in collisions of ${\mathrm{H}}^{+}$ on He at 100 and 200 keV. The electron energy comprised the range from 1 to 16 eV. We present a detailed account of the experimental steps followed in order to obtain confidence in the data. Two features in the angular distribution of the low-energy electron emission were observed: a strong forward-backward asymmetry that gets smaller at higher projectile energy, and a minimum around θ=120°.

We point out that Zak’s kq representation is a good candidate for describing the squeezing caused by a change of lattice constant C, where k is the wave vector within the Brillouin zone and q is the position within an atomic cell. The coordinate eigenstate expansion of ‖kq${\mathrm{〉}}_{\mathit{C}}$ and the technique of integration within an ordered product of operators are employed to derive the squeezing transition from ‖kq${\mathrm{〉}}_{\mathit{C}}$ to ‖kμ,q/μ${\mathrm{〉}}_{\mathit{C}/\mathrm{\mu }}$, where C/μ is the new lattice constant. A comparison of lattice squeezing with the well-known squeeze operator in quantum optics is made. The squeezing in the ‖kq${\mathrm{〉}}_{\mathit{C}}$ representation manifestly exhibits mutually inverse transformations both in the direct lattice vector space and in the reciprocal lattice vector space.

A recent paper by T. Yamazaki and K. Ohtsuki [Phys. Rev. A 45, 7782 (1992)] discusses properties of antiprotonic helium (${\mathrm{He}}^{2+}$p¯${\mathit{e}}^{\mathrm{-}}$) formed in collisions of antiprotons (p¯) with helium. Here we point out problems with approximations and assumptions used in deriving the results of that paper.

Shimamura and Kimura have submitted the preceding Comment [Phys. Rev. A 50, 5346 (1994)], (to be referred to as SK), which criticizes our recent paper [T. Yamazaki and K. Ohtsuki, Phys. Rev. A 45, 7782 (1992)] (to be referred to as YO). In this Reply the authors clarify the purpose of YO and complement its essential points, thus showing that the criticisms of SK are inappropriate.

We present two schemes employing cavity QED phenomena to realize the teleportation of quantum states following the principle outlined by Bennett et al. [Phys. Rev. Lett. 70, 1895 (1993)].

We show that a theoretical description of radial Rydberg wave packets in alkali-metal atoms based solely on hydrogenic wave functions and energies is insufficient to explain data that could be obtained in pump-probe experiments with current technology. The modifications to long-term revival times induced by quantum defects cannot be obtained by direct scaling of the hydrogenic results. Moreover, the effects of laser detuning and quantum defects are different. An alternative approach providing analytical predictions is presented.

We have measured the cold-collision loss rates of laser-trapped Na atoms in each ground-state hyperfine sublevel. The laser intensity dependence for the F=1 sublevel agrees with a simple theory and we establish experimentally that hyperfine-level-changing collision losses are absent as expected. We observed hyperfine-level-changing collisions in the F=2 sublevel but the dependence of the loss-rate constant on laser intensity disagrees with simple theories. Unexpected behavior observed for total trapping laser light intensity between 4 and 12 mW/${\mathrm{cm}}^2$ may be a consequence of the sub-Doppler cooling in the F=2 trap.

Contrary to the results of standard pseudopotential analysis we predict the existence of an alignment transition region in the parameter space of the Paul trap in which the orientation of two-ion crystals with average angular momentum zero is different from x-y or z alignment. This prediction is based on an improved pseudopotential derived by keeping terms up to second order in the micromotion amplitudes. Our analytical predictions are supported by numerical evidence and can be checked experimentally with existing setups.

Dark (bright) planar spatial solitons are predicted for photovoltaic photorefractive materials when the diffraction of an optical beam is exactly compensated by nonlinear self-defocusing (focusing) due to the photovoltaic field and electro-optic effect. These solitons may have steady-state irradiances of microwatts to milliwatts per square centimeter and widths as small as 10 μm in lithium niobate. Optical control is provided by incoherent illumination, and the nonlinear index of a dark soliton may be used to trap a bright soliton by rotating the plane of polarization of the soliton field.

We theoretically demonstrate the feasibility of optimal quasi-phase-matching (QPM) of high-order harmonic generation in gases and plasma with modulated density. QPM optimization, being possible for both tight and loose focusing of the fundamental beam, may increase the conversion efficiency of high-order harmonic generation by several orders of magnitude as compared to the efficiency attainable now.

We demonstrate the existence of population-trapping states in a two-level system driven by a frequency-modulated field. We present detailed numerical results on trapping and also on jumps in the system which occur when the energy levels cross.

In the transmitted beam of a sodium cell with a single feedback mirror highly modulated patterns appear. The patterns possess the dihedral symmetries ${\mathit{D}}_6$, ${\mathit{D}}_2$, and ${\mathit{D}}_3$. More complex patterns consisting of more than one elementary cell show a local hexagonal arrangement. The topological characteristics are very similar to the one of boundary affected patterns predicted in a thin Kerr slice. The instability is due to the competition of diffraction, diffusion, and optical pumping which is influenced by a weak magnetic field. For higher cell-to-mirror distances the observation of an additional length scale indicates a competition between the feedback and a further instability mechanism, probably the counterpropagating beam instability.

The spinless Salpeter equation with the Coulomb potential is solved exactly in momentum space and is shown to agree very well with a coordinate-space calculation. The agreement is so good that it clearly establishes that the procedure discussed can be used to reliably calculate fine-structure effects in any bound-state system without relying on approximations. The procedure works no matter how large the coupling constant. An equation, called the spinless Salpeter equation with retardation, is introduced and this is also able to be solved exactly.

The electromagnetic field is quantized on the basis of the continuous spatial modes of propagation in the direction perpendicular to a plane dielectric slab. The slab has a constant, real, refractive index, and has free space on each side. The quantized fields are used to construct operator representations of the radiation pressure on the slab and the energy and momentum densities that accompany an incident light beam. The roles of the momentum density and the momentum current density are considered in the determination of the radiation pressure on the dielectric slab. The formalism allows the effects of radiation pressure on the motion of the slab to be calculated for any kind of incident light, and it is specifically evaluated for a single-photon wave packet.

An alternative approach to the one-dimensional scattering problem is presented. We show that the reflection and the transmission coefficients of any number of quantum wells or barriers can directly be obtained by using two mathematical methods. The first method arises from a generalization of the so-called elementary symmetric functions used in the mathematical theory of polynomials; the second one consists of a complex generalization of Einstein’s addition law for parallel velocities. These laws for the reflection and transmission amplitude coefficients permit a rapid evaluation of the transmittivity of any kind of potential barrier. Some examples are considered. Results are compared with the ones obtained with the WKB method. We also present a numerical study to test the stability of the method.

From Feynman’s path integral, we derive quasiclassical quantization rules in supersymmetric (SUSY) quantum mechanics. First, we derive a SUSY counterpart of Gutzwiller’s formula, from which we obtain the quantization rule of Comtet, Bandrauk, and Campbell [Phys. Lett. B 150, 159 (1985)] when SUSY is a good symmetry. When SUSY is broken, we arrive at a quantization formula, which is found as good as and even sometime better than the WKB formula in evaluating energy spectra for certain one-dimensional bound state problems. The wave functions in the stationary phase approximation are also derived for SUSY and broken-SUSY cases. Insofar as broken-SUSY cases are concerned, there are strong indications that the new quasiclassical approximation formula always overestimates the energy eigenvalues while WKB always underestimates.

We extend the quantum Monte Carlo wave-function method of quantum optics to non-Markovian system-reservoir interactions. The finite correlation time of the reservoir and the associated memory effects are incorporated into the dynamics by expanding the initial system using fictitious harmonic-oscillator modes, which have Markovian dissipative interactions. The underlying principle is the fact that a class of reservoir spectral functions can be approximated by a finite superposition of Lorentzian functions with positive coefficients.

A consistent method for obtaining the semiclassical multicomponent wave function for any value of adiabatic parameter is discussed and illustrated by examining the motion of a neutral particle in a nonuniform magnetic field. The method generalizes the Bohr-Sommerfeld quantization rule to multicomponent wave functions, and is applied here to the spin-boson model.