The effects of phase-conjugate feedback on semiconductor laser mode structure and dynamics are studied, beginning with a derivation of the system's coherent optical rate equation. For fast-responding phase-conjugating mirror (PCM) a multimode external cavity longitudinal mode spectrum arises that is in many ways similar to that of conventional external feedback lasers, except that the spacing of the external resonator modes equals half that of a conventional external cavity of equal length. A linearized stability analysis based on rate equations for longitudinal modes shows that the external cavity modes alternate in stability as function of increasing frequency shift from the pump. These modes also appear as spikes in the random intensity noise and phase noise spectra. It is shown that the locked phase of the field must be controlled to achieve stable operation, and may be used to maximize the fraction of energy in the central 'spike' of the laser spectrum. Finally, the effects of pump noise on laser linewidth, and the finite PCM response time, are described.

Density-matrix calculations provide the steady-state conditions for probe amplification or lasing between atomic levels with an uninverted population, but additional insight into the underlying physics is given by a probability amplitude approach. In this paper we derive the gain coefficient from the Feynman diagrams for a probe-laser incident on a resonantly pumped, V-type system using time-dependent perturbation theory in a dressed basis. The connection is made to density-matrix calculations for this model, which have been used recently to describe experiments in Rb [A. S. Zibrov et al., Laser Phys. 5, 553 (1995); Phys. Rev. Lett. 75, 1499 (1995)]. In the density-matrix calculation the overall gain is possible because the pump-induced coherence of a strongly driven transition leads to probe amplification, despite the lack of inversion on the probe transition. In our amplitude approach we associate a specific physical process with each of the scattering channels for the probe and show how amplification without inversion can be achieved. The amplitude calculation reveals a distinction between stepwise and two-quantum processes. Interference is shown to result from the two-quantum processes, constructive for the amplification channels and destructive for the absorption. Terms appearing in the gain coefficient are traced to different sources in the amplitude and density-matrix approaches. The physical origin of each term is discussed and compared for both approaches. Terms that arise from coherences in the density-matrix approach are shown to correspond to noninterfering stepwise contributions in the amplitude approach. In deriving these results, we find that the Feynman rules that we construct for forming the probability amplitude for an arbitrary scattering process of the electromagnetic field from the coupled atom-strong pump system are consistent with Rayleigh-Schrödinger perturbation theory in the quantum dressed basis. In addition, the spontaneously emitted photons become entangled with the probe field, correlating the emission spectrum with specific scattering channels.

We show that the quantum Zeno effect (QZE) plays an essential role in discussions of lasing without inversion (LWI) in a V-level scheme. We investigate this role using Monte Carlo wave-function simulations, which provide insight into the physical origin of inversionless lasing. The QZE appears as a result of spontaneous emission and the corresponding collapse of the wave function. Whereas the usual explanation of LWI in terms of quantum interference requires coherence, the QZE explains why incoherent processes are also needed.

The spectral properties of a two-level one-atom laser are investigated in a systematic way below and above threshold. For strong atom-field coupling several different regimes, depending on the pump rate, can be distinguished. The quantum properties of the one-atom laser lead to multipeaked output and fluorescence spectra.

The energy spectrum of the three-particle Hamiltonian obtained by replacing the two-body trigonometric potential of the Sutherland problem by a three-body one of a similar form is derived. When expressed in appropriate variables, the corresponding wave functions are shown to be expressible in terms of Jack symmetric polynomials. The exact solvability of the problem with three-body interaction is explained by a hidden sl(3,R) symmetry.

In a recent paper, Weiss and Kim [Phys. Rev. A 51, 4487 (1995)] have discussed the effects of relativistic corrections on the large atomic number Z behavior of the 1/Z expansion. Contact is established here between their study and the simplest version of density-functional theory in the large Z limit, namely, the Thomas-Fermi theory. It is emphasized that this simple density-functional theory sums subseries of the original 1/Z expansion to all orders in the nonrelativistic case. Relativistic corrections to this density-functional theory are also discussed

A universal scaling law as a function of the projectile charge q and velocity v for the ratio of double to single ionization cross sections of He by fast positive and negative projectiles is presented based on the experimental data.

Electron spectroscopy experiments have been developed by applying coincidence techniques to handle strong background covering a weak signal on photoelectron spectroscopy of free positive ions with synchrotron radiation. 3p inner-shell resonances in 3d excited metastable ${\mathrm{Ca}}^{+}$ could be identified and tentatively assigned.

We report measurements of the absolute differential cross sections for charge-transfer scattering of 0.5-, 1.5-, and 5-keV protons by ${\mathrm{H}}_2$O at laboratory scattering angles between 0.01° and 2.6°. Absolute integral cross sections are also reported and compared to the published total cross sections.

We present in this paper some experiments on the interaction of slow ${\mathrm{N}}^{6+}$, ${\mathrm{O}}^{7+}$, and ${\mathrm{Ne}}^{9+}$ ions below C or Si surfaces carried out by looking at the projectile and target x rays. The study of the x rays emitted by the ions, in contrast with studies of Auger electrons, allows the observation of a much larger part of the decay, not yet explored, below the surface. Moreover, the x rays emitted by the target atoms may identify the shell from which the electrons are captured. It is shown that the electron promotion mechanism, previously observed, which transfers, e.g., K electrons of C targets into the L shell of these ions, represents only a very small part of the interactions occurring at the first atomic layer and that the neutralization takes place, below the surface, mainly via Auger neutralization.

The initial evidence for Bose-Einstein condensation (BEC) of ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ consisted of image distortions that suddenly appeared as the gas was evaporatively cooled to near the transition temperature. We present results of a model of the imaging system used to produce these images. The model confirms that the distortions are a sensitive indicator of BEC, but shows that they make quantitative analysis difficult. We find that the distortions resulted from light scattered by the condensate, in conjunction with aberrations in the imaging lens.

We consider a finite number of noninteracting bosons trapped in an isotropic three-dimensional harmonic oscillator. Using the grand canonical ensemble, we calculate the heat capacity of the system as a function of temperature, for several values of the number of particles. We find that a new definition of critical temperature is necessary for a finite number of trapped particles, and present a definition that is experimentally convenient and in good agreement with a recent definition given by W. Ketterle and N. J. van Druten [Phys. Rev. A 54, 656 (1996)].

We present a theoretical study on the two-color multiphoton ionization of atoms using a nonperturbative method of solving the Schrödinger equation in momentum space. We generalize the problem for absorption of an arbitrary number of ionization photons and especially focus on the absorption of additional above-threshold high-frequency photons. A systematic calculation on the photoelectron energy spectra for the hydrogen atom is performed.

Information about the time-behavior of high-harmonic generation from a single atom in a strong laser field is obtained through a time-frequency analysis. The solution from the full numerical solution of the time-dependent Schrödinger equation is compared with a widely used two-step semiclassical model of harmonic generation. As a test case, we consider a one-dimensional model ``atom'' with a short-range potential. The two results are in qualitative agreement only if in the two-step model the initial and final (dipole) interaction matrix elements are suitably chosen.

We derive a general analytic expression for the harmonic power generated per unit solid angle as a result of scattering plane-wave, circularly polarized light of arbitrary intensity from free electrons moving initially with arbitrary velocity. The relativistic derivation is carried out fully in the laboratory frame.

In a recent article [Phys. Rev. A 53, R1927 (1996)] Wu et al. give a proof of nonlocality for the maximally entangled state of two particles without using inequalities. Here we point out that in order for their argument to go through it is necessary to consider a minimum total of six dimensions in Hilbert space. Indeed, the above argument is found to fail whenever the dimensionality of the product Hilbert space is reduced to four. The explanation for this failure is provided by the fact according to which no direct contradiction between the quantum-mechanical and locally realistic predictions can arise for any fraction of an ensemble of 2×2 systems configured in the maximally entangled state.

We show that, beyond teleportation, it is possible to realize the interchange of states between two quantum systems once their states are simultaneously teleported from one to the other. The experimentally feasible scheme presented here, employing cavity QED phenomena, can be used to realize this ``identity interchange'' process between entangled particles as well, and even to teleport an entanglement from one particle system to another.

The measurement process is taken into account in the dynamics of trapped ions prepared in nonclassical motional states. The induced decoherence is shown to manifest itself both in the inhibition of the internal population dynamics and in a damping of the vibrational motion without classical counterpart. Quantitative comparison with present experimental capabilities is discussed, leading to a proposal for the verification of the predicted effects.