Static electric dipole polarizabilities of lithium clusters made of n $(n=2\mathrm{}–22)$ atoms have been measured. The experiment consists of deflecting a collimated cluster beam through a static inhomogeneous electric field. The strong decrease per atom from Li to ${\mathrm{Li}}_3-{\mathrm{Li}}_4$ shows that electronic delocalization is reached for very small sizes. Moreover, directly measured polarizabilities are consistent with photoabsorption data. They thus confirm unambiguously the “missing” optical strength in lithium clusters.

Microwave emission has been observed at the ground-state hyperfine transition frequency of a cesium atomic vapor driven into a nonabsorbing state by means of coherent population trapping. The coherent emission observed is due to the oscillating magnetization generated by the coherence, which is induced between the ground-state hyperfine levels when they are coupled to an excited state by means of two laser radiations via a Λ scheme. The experiments described were done in a quartz cell containing buffer gases such as neon and nitrogen, reducing the linewidth through the Dicke effect. The cell was placed inside a microwave cavity tuned at 9.2 GHz, the ground-state hyperfine frequency of cesium, and a power output of the order of 100 fW was measured in the case where nitrogen was used as the buffer gas.

We have measured the dc Stark shift of the $6\overrightarrow{S}7S$ transition in atomic cesium using laser spectroscopy. The result of our experiment is $0.7262\left(8\right)\mathrm{}{\mathrm{Hz}\mathrm{}\mathrm{}(\mathrm{V}/\mathrm{c}\mathrm{m})\mathrm{}}^{\mathrm{-}2}.$ This value disagrees with a previous experiment but is within 0.3% of the value predicted by ab initio calculations. This measurement removes the largest outstanding disagreement between experiment and ab initio theory of low-lying states in atomic cesium.

We report a way to overcome heating due to the reabsorption of scattered light when relatively many atoms are laser cooled at high density. A sample of $8\times {10}^7\mathrm{Cs}$ atoms, with $6\times {10}^{11}{\mathrm{atoms}\mathrm{}\mathrm{cm}}^{\mathrm{-}3},$ is loaded into a deep far-detuned one-dimensional optical lattice, which acts as a large volume three-dimensional (3D) trap. Polarization gradient cooling with a separate set of cooling beams is found to work well in this trap, populating the trap’s vibrational ground state with more than half the atoms. After cooling, the lattice is shut off adiabatically, leaving a still dense sample at 1.2 μK. We propose and demonstrate a generalization to a 3D lattice, which will allow many more atoms to be loaded into conservative light traps, and can greatly increase the initial phase-space density for loading magnetic traps.

We report results on inelastic cold collisions for a mixed species magneto-optical trap containing Na and Rb. The rate of collisional trap loss of Na is due to different contributions: Na-Na and Na-Rb collisions. Both parts are investigated with respect to trap laser intensity and frequency. The observations are explained based on a Gallagher-Pritchard model. Possibilities for studies and applications involving mixed species traps are discussed.

We derive a symmetry property for the Fourier transform of the collisionless sound modes of Bose condensates in anisotropic traps connected with a somewhat hidden conservation law. We discuss its possible observation by dispersive light scattering.

We propose an experiment that would demonstrate nonlinear Josephson-type oscillations in the relative population of a driven, two-component Bose-Einstein condensate. An initial state is prepared in which two condensates exist in a magnetic trap, each in a different hyperfine state, where the initial populations and relative phase between condensates can be controlled within experimental uncertainty. A weak driving field is then applied, which couples the two internal states of the atom and consequently transfers atoms back and forth between condensates. We present a model of this system and investigate the effect of the mean field on the dynamical evolution.

We show that a three-photon entangled state can be selected from the product state of an entangled photon pair and a weak coherent state. An experiment producing about 20 counts/sec of three-photon events can be extrapolated from existing results.

We propose the determination of phase-space distributions of optical fields by cascaded optical homodyning, where phase-randomized balanced homodyning is used for measuring the output photon-number statistics of an unbalanced homodyne detection scheme. The phase-space point of interest is controlled by the complex amplitude of the local oscillator and a universal sampling function is sufficient for mapping the measured quadrature statistics onto the phase-space distribution.

A general theory is presented for the spatial correlations in the intensity of the radiation emitted by a random medium in thermal equilibrium. We find that a nonzero correlation persists over large distances, compared to the transverse coherence length of the thermal radiation. This long-range correlation vanishes in the limit of an ideal black body. We analyze two types of systems (a disordered waveguide and an optical cavity with chaotic scattering), in which it should be observable.

Saturated operation of a laser at a wavelength shorter than 6 nm is demonstrated. The output of the Ni-like Dy laser at 5.86 and 6.37 nm, pumped by the VULCAN 1.05-μm Nd-glass laser in a 75-ps double-pulse configuration at $2\times {10}^{13}{\mathrm{W}\mathrm{}\mathrm{cm}}^{\mathrm{-}2}$ peak irradiance, is measured experimentally and studied theoretically using a rate equation and one-dimensional amplified spontaneous-emission model. The experimental results and modeling show that, upon saturation, the output intensities from the lower gain lasing transition at 6.37 nm decrease with increasing gain medium length. This is a different signature of gain saturation for Ni-like lasers and is desirable for applications, as it shows that one lasing transition will dominate with Ni-like lasers in saturation.

We have observed translationally cold electronic ground-state cesium dimers produced directly in a magneto-optical trap and also by photoassociation of cold atoms in this trap. These neutral molecules were detected using photoionization and time-of-flight spectroscopy. Initial experiments indicated a cold molecular formation rate of about $600{\mathrm{s}}^{\mathrm{-}1},$ with no photoassociation laser present. The measured translational temperature of the neutral cesium dimers was approximately 100 μK.

We describe the preparation of Fock states of motion of cesium atoms trapped in potential wells of a far detuned optical lattice. Direct observation of the velocity distribution of the $|n=0\mathrm{}〉$ and $|n=1\mathrm{}〉$ Fock states is obtained by an absorption imaging technique.

The interaction between a polarizable particle and a reflecting wall is examined. A macroscopic approach is adopted in which the averaged force is computed from the Maxwell stress tensor. The particular case of a perfectly reflecting wall and a sphere with a dielectric function given by the Drude model is examined in detail. It is found that the force can be expressed as the sum of a monotonically decaying function of position and of an oscillatory piece. At large separations, the oscillatory piece is the dominant contribution and is much larger than the Casimir-Polder interaction that arises in the limit that the sphere is a perfect conductor. It is argued that this enhancement of the force can be interpreted in terms of the frequency spectrum of vacuum fluctuations. In the limit of a perfectly conducting sphere, there are cancellations between different parts of the spectrum that no longer occur as completely in the case of a sphere with frequency-dependent polarizability. Estimates of the magnitude of the oscillatory component of the force suggest that it may be large enough to be observable.

For all quantum-mechanical potentials that are known to be exactly solvable, there are two different, and seemingly independent methods of solution. The first approach is the potential algebra of symmetry groups; the second is supersymmetric quantum mechanics, applied to shape-invariant potentials, which comprise the set of known exactly solvable potentials. Using the underlying algebraic structures of Natanzon potentials, of which the translational shape-invariant potentials are a special subset, we demonstrate the equivalence of the two methods of solution. In addition, we show that, while the algebra for the general Natanzon potential is so(2,2), the subgroup so(2,1) suffices for the shape invariant subset. Finally, we show that the known set of exactly solvable potentials in fact constitutes the full set of such potentials.

Time-propagation patterns are studied for a network formed by two bands of equidistant rectilinear parallel diabatic potential curves that cross each other. In the case of weak coupling between the bands the propagation proceeds mostly via a diabatic path. In the case of strong coupling a different regime of antidiabatic propagation is revealed. For the intermediate case of coupling strength the propagation is basically described by an overlay of diabatic and antidiabatic patterns; interestingly, the adiabatic propagation is never operative. The present dynamic quantum model is compared with those models that assume a reduction of the problem to a succession of pairwise transitions between the states.

We prove an adiabatic theorem for the ground state of the Dicke model [Phys. Rev. 93, 99 (1954)] in a slowly rotating magnetic field and show that for weak electron-photon coupling, the adiabatic time scale is close to the time scale of the corresponding two-level system without the quantized radiation field. There is a correction to this time scale, which is the Lamb shift of the model. The photon field affects the rate of approach to the adiabatic limit through a logarithmic correction originating from an infrared singularity characteristic of QED.

The much-studied energy-time uncertainty relation has well-known difficulties that are exacerbated for a system with discrete energy levels. The difficulty in representing time in the abstract sense by an operator raises the related question of whether or not there is some other quantity that is complementary to the Hamiltonian of a quantum system. Such a quantity would have dimensions of time but would be a property of the system itself. We examine this question for a system with discrete energy eigenstates for which the ratios of the energy differences are rational. We find that such a quantity does exist and can be represented both by a probability-operator measure and by an Hermitian operator, but in a state space larger than the minimal space needed to include the states of the system. The uncertainty relation with the energy is slightly more complicated than the momentum-position uncertainty relation, but is readily interpretable. To describe such a quantity the name “age” is suggested.

The aim of this paper is to present the interference effects that occur during the time evolution of simple angular wave packets (WP’s) which can be associated with a diatomic rigid molecule (heteronuclear) or with a quantum rigid body with axial symmetry like a molecule or a nucleus. The time evolution is understood entirely within the framework of fractional revivals discovered by Averbukh and Perelman (Phys. Lett. A 39, 449 (1989); Usp. Fiz. Nauk 161, 41 (1991) [Sov. Phys. Usp. 37, 572 (1991)]), since the energy spectrum is exactly quadratic. Our objectives are to study how these interference effects differ when there is a change of the initial WP. For this purpose we introduce a two-parameter set of angular-momentum coherent states. On the one hand, this set emerges quite naturally from the three-dimensional coherent states of the harmonic oscillator; on the other hand, this set is shown to be built from intelligent spin states. By varying one parameter $\left(\eta \right),$ a scenario of interferences occurs on the sphere at fractional parts of the revival time that strongly depend on $\eta .$ For $\eta =\pm 1$ the WP, which coincides with a WP found by Mostowski [Phys. Lett. A 56, 369 (1976)], is a superposition of Bloch [Phys. Rev. 70, 460 (1946)] or Radcliffe [J. Phys. A 4, 313 (1971)] states, and clone exactly in time according to a scenario found for the infinite square well in one dimension, and also for a two dimensional rotor. In the context of intelligent spin states it is also natural to study the evolution by changing $\eta .$ For $\eta =0\mathrm{}$ the WP is called linear, and in time produces a set of rings with axial symmetry over the sphere. The WP’s for other values of $\eta$ are called elliptic, and sets of fractional waves are generated which make a transition between two symmetries. We call these fractional waves “mutants.” For specific times a clone is produced that stands among the mutants. Therefore the change in $\eta$ produces a change in the quantum spread on the sphere. We have also constructed simple coherent states for a symmetric rotor which are applicable to molecules and nuclei. Their time evolution also shows a cloning mechanism for the rational ratio of moments of inertia. For irrational values of this ratio, the scenario of partial revivals completed by Bluhm, Kostelecky, and Tudose [Phys. Lett. A 222, 220 (1996)] is valid.