Photodepletion spectroscopy is used to measure the optical activity of sputtered Ag ionic clusters with up to 70 atoms. With decreasing cluster size the giant resonance caused by collective excitation of the valence electrons shifts to higher frequencies. This blue shift is qualitatively explained in terms of a reduced s-d screening interaction in the surface region of the particles.

We have studied Raman transitions between vibrational levels of atoms confined in the antinodes of a two-dimensional (2D) optical standing wave by means of dipole forces. These transitions are excited by the cooperation of the confining 2D field, with a weak probe laser beam directed through the atomic sample. We experimentally find that the relative line strengths corresponding to transitions from the vibrational ground state to the first and second excited states depend on the polarization of the probe beam. The excitation mechanism is based on a time-modulated distortion of the potential wells. We discuss how the spatial geometry of this distortion depends on the probe polarization, thus qualitatively explaining the experimental observations.

With the help of detailed molecular-dynamics calculations we prove the existence of an instability region I embedded in the single-ion Mathieu stability region M of Paul-trap control parameters a and q. Two-ion crystals do not exist in I. A two-ion crystal created outside of I can be dragged into I by an adiabatic change of a and q. A deterministic order-chaos transition occurs at the point of entry into I. This type of melting transition does not depend on the presence of laser noise and occurs even in the absence of collisions with rest-gas atoms. The prediction can be checked with existing experimental setups.

Quantum fluctuations of a phase-insensitive amplifier are studied when the quantum fluctuations of the input field are correlated with the amplifier’s internal modes. It is found that noise-free quantum amplification can be achieved under certain conditions and only requires finite correlation between the quantum fluctuations of the input field and the amplifier’s internal mode.

We analyze theoretically the quantum beat and the polarization interference phenomena observed as oscillations in pulsed four-wave mixing. We show that resolution of the signal with respect to the delay between the incoming pulses as well as the detection frequency provides valuable information on the nature of the oscillations. Most importantly, it is very simple to distinguish between polarization interference from two independent optical transitions and quantum beats from a three-level system. In case of polarization interference, the phase of the oscillations shifts π when the detected frequency passes any of the resonances. In case of quantum beat, the phase has little dependence on the detected frequency near the resonance.

The analytic solution of the time evolution of a dissipative nonlinear quantum oscillator in the generalized s-ordered representation is derived. The analytical solution allows for comparsion of the various representations with the classical and semiclassical dynamics. It is shown by the eigenvalue analysis of the evolution operators that in the case of a small nonlinearity a semiclassical analysis is an excellent approximation to the exact quantum dynamics. This is further demonstrated by using the Green’s function of the anharmonic oscillator to solve the initial-value problem for a superposition of coherent states.

A modified Franson’s two-photon correlation experiment is discussed. It is shown that the interference in the coincidence detection rate is lost when it is possible to determine the path followed by one of the photons. The interference is recovered when this information is ‘‘erased.’’ The experiment is devised so that the polarization of one of the photons depends on the path followed in the interferometer. Although the path difference is greater than the coherence length, when the two paths are open the photon can be found in a polarization state represented by the superposition of the polarization states associated to the paths. This can be comprehended by considering the situation in which one of the photons is detected before the other can reach the interferometer. In this case, the second photon has to be described by two wave packets simultaneously.

In a two-particle interferometer, one can study the variation of both single- and joint-detection probabilities as functions of the phase shifts of the beams. By combining the usual definition for one-particle fringe visibility ${\mathit{v}}_{\mathit{i}}$ (i=1,2) with a reasonable proposed definition for two-particle fringe visibility ${\mathit{v}}_{12}$, we show that ${\mathit{v}}_{\mathit{i}}^2$+${\mathit{v}}_{12}^2$≤1 or, equivalently, ${\mathit{v}}_{\mathit{i}}$${\mathit{v}}_{12}$≤1/2. Some extensions are discussed.

We propose a family of master equations for local quantum dissipation. The master equations are constructed in the form of Lindblad generators, with the constraints that the dissipation be strictly linear (i.e., Ohmic), isotropic, and translationally invariant. The resulting master equations are given in both the Schrödinger and Heisenberg forms. We obtain fluctuation-dissipation relations, and discuss the relaxation of average kinetic energy to effective thermal equilibrium values. We compare our results for one dimension to the Dekker master equation [H. Dekker, Phys. Rep. 80, 1 (1981)], which can be interpreted as a low-length-scale approximation of our model, as well as the Caldeira-Leggett master equation [A.O. Caldeira and A. J. Leggett, Physica (Utrecht) A 121, 587 (1983)].

Bifurcations found by Leboeuf and Saraceno [Phys. Rev. A 41, 4614 (1990)] in a model Hamiltonian system with SU(3) dynamical symmetry are analyzed in terms of a topological, symmetry-adapted approach. The topological structure of the reduced phase space of the problem, a complex projective space in two dimensions, C${\mathrm{P}}_2$, is used explicitly in the analysis. The study of the action of the finite (additional) symmetry group of the problem leads to a complete classification of stationary solutions and their bifurcations.

We derive the supersqueeze operator for the supersymmetric harmonic oscillator, using Baker-Campbell-Hausdorff relations for the supergroup OSP(2/2). Combining this with the previously obtained superdisplacement operator, we derive the supersqueezed states. These are the supersymmetric generalization of the squeezed states of the harmonic oscillator.

The operations of many detection devices are usually explained in terms of the ionization tracks produced by classical charged particles. A wave-mechanical analysis does not seem to be available. Mott [Proc. R. Soc. London Ser. A 126, 79 (1929)] has shown that an incident α wave emitted by a radioactive nucleus would be scattered by atoms primarily in directions almost forward. However, these scattered waves would appear over the entire sensitive region of the detector. The mechanism that produces a collapse of the wave function to a single track is analyzed here. The incident α wave is written as a superposition of minimum-sized packets. Since it is linear, the Schrödinger equation for the system including an observer can be solved for each packet individually. After the minimum packets interact with the electrons in the detector, they cannot be recombined to form a plane wave. However, they can be combined in groups to form larger coherent packets interacting with the detector to form tracks. The size and shape of each coherent packet is determined by the properties of the medium that is ionized to produce its track. The track from each packet is seen by the observer and is associated with a state of his memory, recording only one track. Each such packet replaces the particle in the usual explanation. These are the packets required to predict the quantum jumps seen in the scattering of laser light from an isolated atom as I have discussed [Phys. Rev. A 45, 4925 (1992)]. The relation of the probability distribution of these tracks to the wave function is explained.

The interaction between an ultrarelativistic particle and a linear array made up of N two-level systems (AgBr molecules) is studied by making use of a modified version of the Coleman-Hepp Hamiltonian. Energy-exchange processes between the particle and the molecules are properly taken into account, and the evolution of the total system is calculated exactly both when the array is initially in the ground state and in a thermal state. In the weak-coupling, macroscopic (N→∞) limit, the system remains solvable and leads to interesting connections with the Jaynes-Cummings model, which describes the interaction of a particle with a maser. The visibility of the interference pattern produced by the two branch waves of the particle is computed, and the conditions under which the spin array behaves as a ‘‘detector’’ are investigated. The behavior of the visibility yields good insights into the issue of quantum measurements: It is found that, in the N→∞ limit, a superselection-rule space appears in the description of the (macroscopic) apparatus. In general, an initial thermal state of the ‘‘detector’’ provokes a more substantial loss of quantum coherence than an initial ground state. It is argued that a system increasingly loses coherence as the temperature of the detector increases. The problem of ‘‘imperfect measurements’’ is also briefly discussed.

The effect of an intracavity accelerating dielectric on the frequencies of counterpropagating waves in a ring laser is calculated and measured. These circulating waves, which are neither harmonic nor propagating in a direction parallel to the motion of the dielectric, have their frequencies determined by the phase velocity in the dielectric. For a nonaccelerating dielectric, the effect of the transverse drag on the frequencies of the counterpropagating waves is measured.

We consider a Pauli particle in a Coulomb field. The supersymmetric Hamiltonian is constructed by explicitly giving the two supercharges ${\mathit{Q}}_1$ and ${\mathit{Q}}_2$ in the full three-dimensional space. These, together with the Hamiltonian, are shown to constitute an s(2) superalgebra. This offers an alternative way of grouping the energy eigenstates into irreducible representations of this symmetry group of the Hamiltonian.

The many-electron problem in a spin-orbital basis of rank K, with a Hamiltonian exhibiting the unitary group U(K) (the coherence group), global symmetry is treated as a detailed example of the technique often referred to as the 1/K expansion. This approach introduces a free parameter K, which is a measure of the number of dynamical variables and usually also invokes coherent states associated with the coherence group. We choose the Thouless coherent state, transform the complex state parameters so that they exhibit the structure of a flat generalized phase space, and analyze the corresponding energy functional as a power series in 1/K. The limit of large K and that of a large number of electrons are discussed and compared to the expected classical limit.

The interaction of ${\mathrm{Ar}}^{17+}$ ions on metallic surfaces has been studied at various incidence angles by looking at the x rays emitted in flight by the ions with a crystal spectrometer. A model has been developed to describe the behavior of the ions outside the surface, and Dirac-Fock calculations of the Auger rates for states with many electrons in high-n states have been performed. The formation of hollow atoms outside the surface, in high-n states, has been observed at grazing incidence, in contrast to the hollow atoms formed below the surface in lower-n states (n=3–4). The decay to the ground state of these very excited ions outside the surface represents less than 1% of the overall decays.

A finite-basis-set method is introduced for calculations involving an electron in the presence of a finite-size nucleus. It is found that the inclusion of powers of the form ${\mathit{r}}^{\mathrm{-}\gamma +\mathit{n}}$ in the basis set, where γ is a real number and n an integer, is of fundamental importance, increasing the convergence in the energy eigenvalues by several orders of magnitude in the case of a large nuclear charge. This conclusion applies also to one-electron potential calculations such as Dirac-Hartree-Fock. The method is applied to calculations of the low-lying levels of hydrogenic atoms in strong magnetic fields. For B≲${10}^9$${\mathit{Z}}^2$ G, the finite-nuclear-size correction is of the same order as that for B=0. For B≳${10}^9$${\mathit{Z}}^2$ G, the correction increases linearly with B for the ground state, and assumes a more complicated dependence for the excited states due to the presence of more than one peak in each radial wave function for B=0.

The radiative-decay rates of the 2${\mathit{s}}^2$2p${(}^2$${\mathit{P}}^0$)-2s2${\mathit{p}}^2$${(}^4$P) intersystem transitions of ${\mathrm{C}}^{+}$ ions have been measured by recording the time dependence of the ∼233-nm emission. A cylindrical radio-frequency ion trap was used to store electron-impact-produced ${\mathrm{C}}^{+}$ ions. The time-dependent signals were analyzed by multiexponential least-squares fits to the data. The measured radiative-decay rates to the ground term are 146.4(+8.3,-9.2) ${\mathrm{s}}^{\mathrm{-}1}$ for ${}_{}{}^4{}_{}{}^{}\mathrm{P}_{1/2}^{}{}_{}{}^{}$, 11.6(+0.8,-1.7) ${\mathrm{s}}^{\mathrm{-}1}$ for ${}_{}{}^4{}_{}{}^{}$${\mathit{P}}_{3/2}$, and 51.2(+2.6,-3.5) ${\mathrm{s}}^{\mathrm{-}1}$ for ${}_{}{}^4{}_{}{}^{}$${\mathit{P}}_{5/2}$. Comparison of the measured values with theoretical values is presented.

Experimental data are presented for differential electron emission from helium induced by isotachic ${\mathrm{H}}^{+}$ and ${\mathrm{He}}^{2+}$ impact. Electron emission at 15° was studied in order to investigate maxima in the ${\mathit{d}}^2$σ/${\mathit{dv}}_{\mathit{e}}$dΩ spectra. These maxima were previously observed to shift to lower electron velocities as the projectile charge state increased and the shifts were interpreted as evidence of an independent saddle-point-ionization mechanism. The present data for ${\mathrm{H}}^{+}$ and ${\mathrm{He}}^{2+}$ impact do not confirm any such shifts and indicate that previous ${\mathrm{He}}^{2+}$ measurements, where shifts were observed, are in error.