We observed the free-induction decays in the ground state of Cs atoms in a thin glass cell. The line narrowing of magnetic resonance is theoretically and experimentally presented as a function of the time interval between the pump and probe pulses. The atoms moving parallel to the windows are found to have long-lived polarization and coherence. The above phenomena are characteristic of the vacuum cell in contrast to those of the buffer gas cell.

We present a practical scheme of preparing a temporally stationary single-photon-trapped state. A special dynamics at two-photon resonance in the coupled atom-cavity system, where a two-level atom is driven by a classical field, is investigated for this purpose. It is found that significant atomic damping is required, rather than avoided, to establish the one-photon Fock state. We analytically derive the optimal conditions in the large detuning limit.

A number of transitions in two-color resonant four-wave mixing spectra of the OH- and NH-containing flames are observed for pairs of rovibronic states without a common level. A theory is developed to show how rotationally inelastic collisions perturb the ground- and upper-state gratings and trigger new signals in equilibrium gases. The collisional alignment rate of a particular state-to-state transition in the ground vibronic state of NH is spectroscopically derived.

We have performed a series of calculations of the photoabsorption cross section of ${\mathrm{Fe}}^{14+}$ near the ${2p}^{-1}$ and ${2s}^{-1}$ edges, within the framework of R-matrix theory. We find the unexpected result that the inclusion in the calculation of such effects as the spin-orbit interaction and higher-order correlations leads to a mere redistribution of flux among the various final channels, while the total convoluted photoabsorption cross section remains virtually unchanged. Hence, an appropriate minimal configuration $\mathrm{LS}$ coupling representation can adequately describe inner-shell total photoabsorption cross sections, leading to a saving in computational effort by orders of magnitude compared to more elaborate calculations.

The motion of neutral particles with magnetic moments in an inhomogeneous magnetic field is described in a semiclassical framework. The concept of coherent internal states is used in the formulation of the semiclassical approximation from the full quantum-mechanical expression. The classical trajectories are defined only for certain spin states, that satisfy the conditions for being coherent internal states. The reliability of Stern-Gerlach experiments to measure spin projections is assessed in this framework.

The repulsive Coulomb barrier (RCB) for electron emission is a general property of multiply charged anions. When an electron is emitted from a multiply charged anion, the electron experiences short-range attraction by the nuclei and long-range repulsion from the remaining negatively charged system, giving rise to the RCB. Although the RCB is dominated by the electrostatic forces present, it is argued that the exact potential the electron experiences is nonlocal and energy dependent. The theory of the RCB is outlined and related to the theory of Green’s functions. Since it is complicated to compute a nonlocal and energy-dependent potential, approximation schemes are introduced that allow convenient calculation of local energy-independent RCB potentials. Three approximation schemes of complementary nature are proposed. The physical meaning of these schemes, the underlying approximations, and their possible weaknesses are discussed in detail. The local approximation schemes are used to calculate the RCB of atomic dianions ${\mathrm{F}}^{2\mathrm{-}}$ and ${\mathrm{O}}^{2\mathrm{-}}$ and of the linear carbon cluster dianions ${\mathrm{C}}_n^{2-}$ $\mathrm{}(n=2,4,6,8\mathrm{}).$ The atomic dianions serve as convenient objects to study the basis-set dependence of the local approximation schemes. The computed local potentials of the carbon dianions are used to calculate their lifetimes in the framework of Wentzel-Kramer-Brillouin theory. We found that the lifetime of the linear carbon dianions grows markedly when going from ${\mathrm{C}}_2^{2\mathrm{-}}$ to ${\mathrm{C}}_8^{2\mathrm{-}},$ and that the latter should be the only species observable in a mass spectrometer. This agrees with the available experimental findings.

A rotating-wave approximation (RWA) is developed to describe the evolution of a two-level system, which has permanent dipole moments, interacting with a pulsed laser. Comparisons with exact calculations for one- and two-photon excitations involving the two lowest vibrational states of the ground electronic state of ${\mathrm{HeH}}^{+}$ are given to illustrate the validity of the RWA formula.

The recent first-principles derivation of Langevin-Bloch equations of motion for near-resonant atoms embedded in a linear dielectric host leads to a clear, direct physical reinterpretation of fundamental physical principles as applied to one of the most basic problems of quantum mechanics: the renormalization of the spontaneous emission rate of an atom in a dielectric host. Here we show the role of the Lorentz local field, the fluctuation-dissipation theorem, the wave number and wave vector, the density of states, Fermi’s golden rule, the electromagnetic energy density, canonical quantization, and the classical constitutive relations in this context.

A linear quantum dynamical theory for squeezing the output of the trapped Bose-Einstein condensate is presented with the Bogoliubov approximation. We observe that the nonclassical properties, such as sub-Poisson distribution and quadrature squeezing effect, mutually oscillate between the quantum states of the applied optical field and the resulting atom laser beam with time. In particular, it is shown that an initially squeezed optical field will lead to squeezing in the outcoupled atomic beam at later times.

The scalar Stark shift of the 254-nm intercombination $6{}^1{\mathrm{S}}_0\to 6{}^3{\mathrm{P}}_1$ line in Hg was measured using a Doppler-shift frequency calibration technique. It is equal to $-3.32\pm 0.06$ $\mathrm{kHz}/(\mathrm{k}\mathrm{V}/\mathrm{c}\mathrm{m}{)}^2.$ This measurement can be used to test more accurate calculations of Hg atomic wave functions.

Two recent experiments have reported the trapping of individual atoms inside optical resonators by the mechanical forces associated with single photons [Hood et al., Science 287, 1447 (2000); Pinkse et al., Nature (London) 404, 365 (2000)]. Here we analyze the trapping dynamics in these settings, focusing on two points of interest. First, we investigate the extent to which light-induced forces in these experiments are distinct from their free-space counterparts, and whether or not there are qualitatively different effects of optical forces at the single-photon level within the setting of cavity QED. Second, we explore the quantitative features of the resulting atomic motion, and how these dynamics are mapped onto experimentally observable variations of the intracavity field. Toward these ends, we present results from extensive numerical simulations of the relevant forces and their fluctuations, as well as a detailed derivation of our numerical simulation method, based on the full quantum-mechanical master equation. Not surprisingly, qualitatively distinct atomic dynamics arise as the coupling and dissipative rates are varied. For the experiment of Hood et al., we show that atomic motion is largely conservative and is predominantly in radial orbits transverse to the cavity axis. A comparison with the free-space theory demonstrates that the fluctuations of the dipole force are suppressed by an order of magnitude. This effect is based upon the Jaynes-Cummings eigenstates of the atom-cavity system and represents distinct physics for optical forces at the single-photon level within the context of cavity QED. By contrast, even in a regime of strong coupling in the experiment of Pinkse et al., there are only small quantitative distinctions between the potentials and heating rates in the free-space theory and the quantum theory, so it is not clear that a description of this experiment as a novel single-quantum trapping effect is necessary. The atomic motion is strongly diffusive, leading to an average localization time comparable to the time for an atom to transit freely through the cavity, and to a reduction in the ability to infer aspects of the atomic motion from the intracavity photon number.

We present quantum phase transitions and critical phenomena of three-body Coulomb systems with charges $(Q,$ q, $Q)$ and masses $(M,$ m, $M).\mathrm{}$ Full numerical results, using the finite-size scaling method, for an arbitrary mass ratio $0<~\kappa {=(1+m/M)\mathrm{}}^{-1}<~1$ over the range $1<~\lambda =|Q/q|<~1.25,$ show that there exists a transition curve ${\lambda }_c\left(\kappa \right)$ through which all systems undergo a first-order phase transition from stable to unstable. Particularly, ${\lambda }_c\left(\kappa \right)$ has a minimum at ${\kappa }_m=0.35,$ which leads to a new proposed classification of the three-body Coulomb systems: moleculelike systems, $\kappa >{\kappa }_m,$ such as ${\mathrm{Ps}}^{-}$ $(\kappa =0.5)$ and atomlike systems, $\kappa <{\kappa }_m,$ such as $\overline{p}\overline{p}d$ $(\kappa =0.33).\mathrm{}$

By considering the stability of potential flow of a superfluid around large obstacles of size R, we derive an analytical result for the critical velocity that is of order $v_c\sim ħ/mR,$ scaling inversely with obstacle size, in contrast to what is obtained from a Landau criterion. Our results are compared with numerical solutions of the Gross-Pitaevskii equation and with recent measurements of the critical velocity in Bose-Einstein condensates of dilute atomic gases.

We consider a model of N two-dimensional bosons in a harmonic potential with weak repulsive δ-function interactions. We show analytically that, for angular momentum $L<~N,$ the elementary symmetric polynomials of particle coordinates measured from the center of mass are exact eigenstates with energy $N(N-L/2\mathrm{}-1).$ Extensive numerical analysis confirms that these are actually the ground states, but we are currently unable to prove this analytically. The special case $L=N$ can be thought of as the generalization of the usual superfluid one-vortex state to Bose-Einstein condensates in a trap.

We study the dynamics of a multimode laser diode with delayed optical feedback operating in the low-frequency fluctuations regime. We show that a multimode extension of the Lang-Kobayashi equations that takes into account spontaneous emission noise predicts two qualitatively different behaviors of the laser on the picosecond time scale. Individual modes of the laser can emit pulses in-phase or oscillate out-of-phase, depending on the operating parameters. The corresponding statistical distributions are in good agreement with two recent experiments.

The focusing of the vacuum modes of a quantized field by a parabolic mirror is investigated. We use a geometric optics approximation to calculate the energy density and mean-squared field averages for scalar and electromagnetic fields near the focus. We find that these quantities grow as an inverse power of the distance to the focus. There is an attractive Casimir-Polder force on an atom which will draw it into the focus. Some estimates of the magnitude of the effects of this focusing indicate that it may be observable.

A cellular quantum computer with a spin qubit and ancilla bits in each cell is proposed. The whole circuit works only with the help of external optical pulse sequences. In the operation, some of the ancilla bits are activated, and autonomous single-and two-qubit operations are made. In the sleep mode of a cell, the decoherence of the qubit is negligibly small. Since only two cells at most are active at once, the coherence can be maintained for a sufficiently long time for practical purposes. A device structure using a coupled-quantum-dot array with possible operation and measurement schemes is also proposed.

Multichannel quantum defect theory (MQDT) is used to calculate highly excited predissociated and preionized triplet gerade states of ${\mathrm{H}}_2.$ The treatment is ab initio and is based on the clamped-nuclei quantum-defect matrices and dipole transition moments derived from quantum-chemical potential energy curves by Ross et al. [Can. J. Phys. (to be published)]. Level positions, predissociation or preionization widths and relative intensities are found to be in good agreement with those observed by Lembo et al. [Phys. Rev. A 38, 3447 (1988); J. Chem. Phys. 92, 2219 (1990)] by an optical-optical double resonance photoionization or depletion technique.

The Dirac exchange energy $E_x$ has a density ${\varepsilon }_x\mathrm{}\left(r\right)\mathrm{}$ in a spherically symmetric ten-electron atomic ion that is determined by the idempotent first-order density matrix (1 DM). In turn, this 1 DM has as its leading term in the $1/Z$ expansion, with Z the atomic number, the bare Coulomb result. This latter quantity is known analytically from the study of March and Santamaria [Phys. Rev. A 38, 5002 (1988)]. Here ${\varepsilon }_x\mathrm{}\left(r\right)\mathrm{}$ is calculated analytically, and presented graphically for $Z=92\mathrm{}$ in this large-Z limit. The Slater approximation to the exchange potential $V_x\left(\mathbf{r}\right),$ namely, $V_{\mathrm{Sla}}\left(\mathbf{r}\right)=2\mathrm{}{\varepsilon }_x\mathrm{}\left(r\right)/\rho \mathrm{}\left(r\right)\mathrm{}$ with $\rho \mathrm{}\left(r\right)\mathrm{}$ the ground-state electron density, is also plotted for $Z=92.\mathrm{}$ In the large-Z limit, $V_x\left(\mathbf{r}\right)$ can be obtained by functional differentiation of the resultant exchange energy, and is expressed in terms of electron and kinetic-energy densities. Numerical calculations, based on $V_{\mathrm{Sla}}\left(\mathbf{r}\right)$ plus approximate corrections, are also presented.

We report on a detailed experimental and theoretical study of electron-impact ionization of ${\mathrm{O}}^{5+}$ ions. A high-resolution scan measurement of the K-shell excitation threshold region has been performed with statistical uncertainties as low as 0.03%. At this level of precision a wealth of features in the cross section arising from indirect ionization processes becomes visible, and even interference of direct ionization with resonant-excitation/auto-double-ionization (READI) is clearly observed. The experimental results are compared with R-matrix calculations that include both direct and indirect processes in a unified way. Radiative damping of autoionizing Li-like states is found to be about 10–15 %. The calculations almost perfectly reproduce most of the experimental resonance features found in the present measurement including READI. They also agree with the direct-ionization converged close-coupling results of I. Bray [J. Phys. B 28, L247 (1995)] and the absolute total ionization cross section measurement of K. Rinn et al. [Phys. Rev. A 36, 595 (1987)].