We study the cooperative effects in a one-photon micromaser with atomic polarization. We find that the injected polarization makes the micromaser more insensitive to cooperative effects as compared to the unpolarized case. Although probability diffusion in phase space takes place and spikes develop in the average photon number, the squeezing properties of the cotangent states are more affected by the cavity losses than by the presence of two atoms in the micromaser cavity.

The steady-state properties of a dye laser model with white quantum noise and strongly colored pump noise are investigated. An effective diffusion coefficient in the steady state is presented. Our coefficient differs from that of Fox and Roy [Phys. Rev. A 35, 1838 (1987)]. We compare our results with the measurements and simulations of Lett, Short, and Mandel [Phys. Rev. Lett. 52, 341 (1984)], and the results of Fox and Roy, respectively. We find that the quantum noise plays an important role in the steady-state analysis of laser fluctuations below and near threshold.

A proposal for realizing one- and two-mode degenerate Raman coupled models, of the type proposed by Knight [Phys. Scr. T 12, 51 (1986)] in the context of quantum optics, for the motion of a trapped two-level ion, is presented. The interaction has a dispersive effect on the vibrational motion of the ion. For the one-mode case, an initial vibrational coherent state evolves into superpositions of coherent states (Schrödinger-cat states) correlated with the internal states of the ion. In the two-mode case, with initial coherent states in each mode, entanglements of coherent states between the modes correlated with the internal ionic states are obtained. Detection of such states is briefly discussed.

An algorithm for quantum-state estimation based on the maximum-likelihood estimation is proposed. Existing techniques for state reconstruction based on the inversion of measured data are shown to be overestimated since they do not guarantee the positive definiteness of the reconstructed density matrix.

Upper and lower bounds are established for time-dependent ensemble averages of observables of driven quantum systems in mixed states. They limit controllability of observables independently of the control fields. Narrower bounds are established when the observable is a projector onto a pure quantum state or subspace. They are optimal in the sense of being kinematically achievable. Calculations on nonlinear optimal control of a four-level model indicate that these kinematical bounds are dynamically achievable asymptotically with increasing control pulse strength.

Rovibrational levels (v=0–30) of the $0_{\mathrm{g}}^{\mathrm{-}}$ ``pure long-range'' state of ${}_{}{}^{39}{}_{}{}^{}\mathrm{K}_2^{}{}_{}{}^{}$ are observed by photoassociative spectroscopy of ultracold potassium atoms prepared in a high-density magneto-optical trap. The measured molecular binding energies are used to precisely determine the long-range dipole-dipole potential constant ${\mathrm{C}}_3^{\mathrm{\Pi }}$ of the K(4s)+K(4p) asymptote and the radiative lifetime of the 4p state. We determine ${\mathrm{C}}_3^{\mathrm{\Pi }}$=-5.456(9) zJ ${\mathrm{nm}}^3$ (-8.445(14) a.u.), τ(4${\mathrm{}}^2$${\mathrm{P}}_{3\mathrm{/}2}$)=26.34(5) ns, and τ(4${\mathrm{}}^2$${\mathrm{P}}_{1\mathrm{/}2}$)=26.69(5) ns. Our result is a significant improvement in precision over previous lifetime measurements and agrees well with the recent fast-beam experiment [U. Volz and H. Schmoranzer, Phys. Scr. T65, 48 (1996)].

It is demonstrated that the nonadiabatic coupling between two quasiresonant molecular states of the (${\mathrm{Z}}_1$,e,${\mathrm{Z}}_2$) system is provided by the hidden crossing of corresponding potential-energy surfaces in the complex plane of internuclear distance. It is shown that the coupling interaction used in the standard Demkov model is correct within a logarithmic accuracy. The semiempirical value of the Massey parameter in the Meyerhof formula for the K-K vacancy sharing ratio is derived from the characteristics of the 1sσ-2pσ hidden crossing. It is also shown that the 2pσ-3dσ hidden crossing produces a maximum in the K-K vacancy sharing ratio at the higher collision velocities even under quasiresonance conditions.

A technique for storage of fast-ion beams (keV) using only electrostatic fields is presented. The fast-ion trap is designed like an optical resonator, whose electrode configuration allows for a very large field-free region, easy access into the trap by various probes, a simple ion loading technique, and a broad acceptance range for the initial kinetic energies of the ions. Such a fast-ion storage device opens up many experimental possibilities, a few of which are presented.

We use the Bogoliubov-Hartree theory to describe low-energy excitations of trapped Bose condensates. We construct the quasiparticle spectrum and the quasiparticle operators explicitly in terms of the bare atomic operators. Our results reveal interesting properties of spatially confined Bose condensates and are in excellent agreement with recent experiments.

We study the spectral properties of three-dimensional Rydberg states of atomic hydrogen in a microwave field of linear polarization. We identify a novel structure in the Floquet spectrum as the ``backbone'' of the experimentally observed ionization process. Localization properties, energies, and lifetimes of the individual Floquet states are shown to faithfully reflect the structure of classical phase space, which can be described by a perturbative approach.

We study the elastic scattering length and inelastic decay rate associated with collisions of ${}_{}{}^{23}{}_{}{}^{}\mathrm{Na}$ and ${}_{}{}^{87}{}_{}{}^{}\mathrm{Rb}$ atoms in different hyperfine states: one with atoms in the |f=2,${\mathrm{m}}_{\mathrm{f}}$=2〉 and one with atoms in the |f=1,${\mathrm{m}}_{\mathrm{f}}$=-1〉 state. For Na the real part of the ${\mathrm{a}}_{\mathrm{}\left(22\right)+\left(1\mathrm{}\mathrm{-}1\right)}$ scattering length for |22〉+|1-1〉 collisions is predicted to be positive and equal to 65±5 Bohr length units ${\mathrm{a}}_0$ for small B. The zero-temperature low-field decay rate is of the order of a typical exchange rate: ${\mathrm{G}}_{\mathrm{}\left(22\right)+\left(1\mathrm{}\mathrm{-}1\right)}$=(1.5±0.7)${10}^{\mathrm{-}11}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$, showing that a two-condensate experiment is not feasible for a Na gas sample in a static magnetic trap. For the case of Rb atoms the present knowledge of the singlet interaction does not allow a similar calculation. The extreme suppression of ${\mathrm{G}}_{\mathrm{}\left(22\right)+\left(1\mathrm{}\mathrm{-}1\right)}$ demonstrated by a recent experiment is shown to be very restrictive for the value of the singlet accumulated phase.

Numerical calculations of the harmonic yield from diatomic molecular ions initially prepared in a highly excited vibrational state show a remarkable enhancement of the harmonic energies in the plateau in terms of the ponderomotive energy. The two-step scheme that explains the mechanism of harmonic generation by atoms is extended to our double potential-well structure, providing an explanation for the high photon energies produced.

We consider the dynamics of a neutral atom of magnetic moment μ in a spatially dependent magnetic field. Interaction with a resonant radio frequency introduces a peculiar nonlinear dynamics for the slow motion of the center of mass. We derive asymptotically exact equations for the slow dynamics, which are compared to the numerical solution of the full nonlinear problem. We also calculate the frequency of small oscillations for resonant trapped motions.

We investigate theoretically the amplification of a laser beam propagating through a collection of Doppler-broadened two-level atoms driven by an intense counterpropagating laser beam. Large amplification of the beam is predicted when the pump-beam Rabi frequency is comparable to the Doppler width of the atomic transition, even without including the effects of atomic recoil. The microscopic origin of the gain can be attributed to the coherent driving of the atomic dipole moment, suggesting that amplification and lasing due to collective atomic recoil may be influenced by this process.

Measurements of quantum correlations are reported for a frequency difference of 25 THz between the signal and idler output fields generated by a subthreshold nondegenerate optical parametric oscillator. By simultaneously exciting a two-photon transition in atomic Cs by a combination of signal, idler, and ``references oscillator'' fields, we record modulation of the excited-state population due to quantum interference between two alternative excitation pathways. The observed phase-sensitive modulation is proportional to the correlation function 〈E-|${\mathrm{Ax}}_{\mathrm{s}}$E-|${\mathrm{Ax}}_{\mathrm{i}}$〉 for the quantized signal and idler fields.

We propose and demonstrate a method for determining the two-time photon-number correlations of an optical field on ultrafast time scales. The method, which uses dual-pulse, phase-averaged, balanced-homodyne detection, is sensitive at the single-photon level and can have a quantum efficiency approaching 100%. Using this method we have determined the two-time, photon-number correlations on subpicosecond time scales of emission from a semiconductor optical amplifier.

The ratio of scalar to tensor transition polarizabilities (α/Β) for the cesium ${6\mathrm{S}}_{1\mathrm{/}2}$F=3 to ${7\mathrm{S}}_{1\mathrm{/}2}$F′=3 transition has been measured using a spin-polarized atomic beam and an interference technique. We use an electric- and magnetic-field configuration where the Stark-induced electric dipole transition amplitudes arising from the scalar and tensor polarizabilities interfere, giving rise to large changes in the 6S-7S transition rate. The measured ratio is α/Β=-9.905±0.011. This result represents a tenfold improvement in precision, and agrees well with previous measurements and calculations. The ratio α/Β is of critical importance for cesium atomic parity violation experiments.

The average time delay in electromagnetic scattering by a spherically symmetric, reflection-invariant, nonabsorbing scatterer is evaluated, extending results previously derived for scalar nonrelativistic scattering. For the lth partial wave in each polarization, the time delay is the spectral average of d${\mathrm{\eta }}_{\mathrm{l}}$/dω over the incident wave packet (where ${\mathrm{\eta }}_{\mathrm{l}}$ is the corresponding phase shift and ω the angular frequency). This is one-half of the Eisenbud-Wigner nonrelativistic expression. The relationship with angular time delay in a given direction is also discussed.

We have performed close-coupling calculations on electron scattering by Ca atoms and on photodetachment of ${\mathrm{Ca}}^{\mathrm{-}}$ ions by using a six-state ${(}^1$S- ${}_{}{}^3{}_{}{}^{}\mathrm{-}$ ${}_{}{}^3{}_{}{}^{}\mathrm{-}$ ${}_{}{}^1{}_{}{}^{}\mathrm{-}$ ${}_{}{}^1{}_{}{}^{}\mathrm{-}$ ${}_{}{}^1{}_{}{}^{}\mathrm{P}$) R-matrix method. We predict a strong interaction between (${4\mathrm{s}}^{21}$S+εd${)}^2$D and (${4\mathrm{s}4\mathrm{p}}^3$P+εp${)}^2$D channels that gives rise to two relatively broad resonance peaks in the d-wave cross section. In addition, one obtains a strong and a weak peak in the total scattering cross section. Our calculations on the photodetachment cross section of ${\mathrm{Ca}}^{\mathrm{-}}$ ions yield results that are in good qualitative agreement with the experimental data by allowing for the opening of a detachment channel connected to the excited state ${4\mathrm{s}4\mathrm{p}}^3$P.