A scissors mode of a rotating Bose-Einstein condensate is investigated both theoretically and experimentally. The condensate is confined in an axisymmetric harmonic trap, superimposed with a small rotating deformation. For angular velocities larger than ${\omega }_{\perp }/\sqrt{2},$ where ${\omega }_{\perp }$ is the radial trap frequency, the frequency of the scissors mode is predicted to vanish like the square root of the deformation, due to the tendency of the system to exhibit spontaneous rotational symmetry breaking. Measurements of the frequency confirm the predictions of theory. Accompanying characteristic oscillations of the internal shape of the condensate are also calculated and observed experimentally.

This paper is devoted to the study of the influence of two parallel plates on the atomic levels of a hydrogen atom placed in the region between the plates. We treat two situations, namely, the case where both plates are infinitely permeable and the case, where one of them is a perfectly conducting plate and the other, an infinitely permeable one. We compare our result with those found in literature for two parallel conducting plates. The limiting cases where the atom is near a conducting plate and near a permeable one are also taken.

The generalized oscillator strengths (GOS’s) for quadrupole and monopole (and their sums) excitation of the outer $n\overrightarrow{p}\mathrm{}(n+1\mathrm{})p,(n+2\mathrm{})p$ levels of the noble gas atoms Ne, Ar, Kr, and Xe are investigated over the broad range of momentum transfer q values, from $q=0\mathrm{}$ up to $q=8\mathrm{}\mathrm{a}.\mathrm{u}.\mathrm{},$ the region of their accessibility. The purpose of this investigation is to understand and delineate the relative contributions to the GOS of the various discrete transition multipolarities to guide measurements. This study has been motivated by recent absolute measurements of the GOS’s for the lowest nondipole discrete transition in Ar [X. W. Fan and K. T. Leung, Phys. Rev. A 62, 062703 (2000)] and their subsequent reinterpretation.. The calculations are performed in the one-electron Hartree-Fock approximation and with many-electron correlation effects taken into account within the random phase approximation with exchange for the quadrupole and monopole excitations. We find that the GOS’s for the quadrupole $n\overrightarrow{p}\mathrm{}(n+1\mathrm{})p$ transitions of Ne, Ar, Kr, and Xe are characterized by two maxima, while the corresponding GOS’s for monopole excitations have only a single maximum.

We present semiclassical descriptions of Bose-Einstein condensates for configurations with spatial symmetry, e.g., cylindrical symmetry, and without any symmetry. The description of the cylindrical case is quasi-one-dimensional (Q1D), in the sense that one only needs to solve an effective 1D nonlinear Schrödinger equation, but the solution incorporates 3D aspects of the problem, as a result of which the 1D equation is supplemented by a noncanonical (quartic) normalization condition. The solution in classically allowed regions is matched onto that in classically forbidden regions by a connection formula that properly accounts for the nonlinear mean-field interaction. Special cases for vortex solutions are treated too. Comparisons of the Q1D solution with the full 3D and Thomas-Fermi ones are presented, and conditions for the applicability of the effective low-dimensional equations are obtained.

We investigate the steady-state spontaneous emission of a V-type three-level atom, with the coherence between the two upper levels modified and controlled via incoherent pumping to a fourth auxiliary level. The external pumping gives us an easily controllable handle in manipulating the spontaneous emission to such an extent that, under certain conditions, complete quenching of spontaneous emission is possible. We also show that even the interference between the decay channels, which is considered a key requirement in spontaneous emission quenching through quantum interference, is not essential to achieve near 100% trapping and almost complete suppression of spontaneous emission. Thus we provide a scheme for spontaneous emission quenching which can be easily realized experimentally.

A nonlinear Schrödinger equation is derived for the dynamics of a beam of ultracold fermionic atoms traversing a Bose-Einstein condensate. The condensate phonon modes are shown to provide a nonlinear medium for the fermionic atoms. A two-fermion bound state is predicted to arise, and the signature of the bound state in a nonlinear atom optics experiment is discussed.

We consider environment induced decoherence of quantum superpositions to mixtures in the limit in which that process is much faster than any competing one generated by the Hamiltonian $H_{\mathrm{sys}}$ of the isolated system. This interaction-dominated decoherence limit is of importance for the emergence of classical behavior in the macroscopic domain, since it will always be the relevant regime for large enough separations between the superposed wave packets. The usual golden-rule treatment then does not apply, but we can employ a short-time expansion for the free motion while keeping the interaction $H_{\mathrm{int}}$ in full. We thus reveal decoherence as a universal short-time phenomenon largely independent of the character of the system as well as the bath and of the basis the superimposed states are taken from. Simple analytical expressions for the decoherence time scales are obtained in the limit in which decoherence is even faster than any time scale emerging from the reservoir Hamiltonian $H_{\mathrm{res}}.$

Environment induced decoherence entails the absence of quantum interference phenomena from the macroscopic world. The loss of coherence between superposed wave packets is a dynamical process the speed of which depends on the packet separation: The farther the packets are apart, the faster they decohere. The precise temporal course depends on the relative size of the time scales of decoherence and other processes taking place in the open system and its environment. We use the exactly solvable model of a harmonic oscillator coupled to a bath of harmonic oscillators to illustrate various decoherence scenarios: These range from exponential golden-rule decay for microscopic superpositions, system-specific decay for larger separations in a crossover regime, and finally the universal interaction-dominated decoherence for ever more macroscopic superpositions investigated in great generality in the accompanying Paper I [W. T. Strunz, F. Haake, and D. Braun, Phys. Rev. A $67,$ $022101$ (2003)].

We report on a quantum interference experiment to probe the coherence between two photons coming from nondegenerate photon pairs at telecom wavelength created in spatially separated sources. The two photons are mixed on a beam splitter and we observe a reduction of up to 84% in the net coincidence count rate when the photons are made indistinguishable. This experiment constitutes an important step towards the realization of quantum teleportation and entanglement swapping with independent sources.

We investigate the generation of multipartite entangled state in a system of N quantum dots embedded in a microcavity and examine the emergence of genuine multipartite entanglement by three different characterizations of entanglement. At certain times of dynamical evolution one can generate multipartite entangled coherent exciton states or multiqubit W states by initially preparing the cavity field in a superposition of coherent states or the Fock state with one photon, respectively. Finally, we study environmental effects on multipartite entanglement generation and find that the decay rate for the entanglement is proportional to the number of excitons.

Absorption band shapes of an asymmetric dimer system constituted by monomers with different excitation energies and optical transition matrix elements are considered in the semiclassical parameter region. Optical transition matrix elements originating from arbitrary initial vibrational states are analyzed on the basis of a spin representation of the eigenstates of an associated symmetry broken spin-boson Hamiltonian. Correlations between the spin-down and spin-up coefficients of these eigenstates are shown to exist and investigated in detail. Using these correlations, an asymmetry interpolation of the intensity of absorption lines between dimer configurations with different optical monomer transition matrix elements is proposed.

The quasifree nonempirical model proposed by Staszewka et al. in 1983 for the imaginary part of the electron scattering optical potential is revised, in order to improve its foundations, accuracy, and range of applicability. The importance of relativistic and many-body effects for heavy atoms is shown and some corrections proposed. A criterion for selecting the Δ parameter is discussed. The model is also shown to admit considerable simplifications without loss of accuracy. Calculated elastic (differential and integral) and inelastic cross sections for He to Xe noble gases and also for ${\mathrm{N}}_2,$ CO, and ${\mathrm{CO}}_2$ molecules are compared to experimental values.

The charge-transfer rate coefficients of ${\mathrm{Fe}}^{3+}$ with ${\mathrm{H}}_2$ and ${\mathrm{N}}_2$ are measured by using a laser-ablation ion source and a quadrupole radio-frequency ion trap with the mean collision energy of about 5.1 eV. The rate coefficients for ${\mathrm{Fe}}^{3+}$ with ${\mathrm{H}}_2$ at the equivalent temperature $1.7\times {10}^3\mathrm{K}$ and ${\mathrm{Fe}}^{3+}$ with ${\mathrm{N}}_2$ at $1.3\times {10}^4\mathrm{K}$ are $1.64\left(0.22\right)\mathrm{}\times {10}^{-10}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ and $4.36\left(0.46\right)\mathrm{}\times {10}^{-9}{\mathrm{cm}}^3{\mathrm{s}}^{-1},$ respectively. The measured values are of the same order as the Langevin rate coefficient.

It is shown that polar molecules colliding with a solid are subject to efficient self-alignment caused by an interaction with their own electrostatic image dipole when the permanent dipole moment of the molecule exceeds 3 D.

We present the fragmentation dynamics of ${\mathrm{CsC}}_n^{-}$ $(n<~10)$ in collision with argon at 15 keV impact energy. The propensity for the formation of the fragment ions ${\mathrm{C}}_m^{-}(m<~n)$ exhibits even-odd oscillations, with the yield being larger when m is even; and this is correlated with the larger electron affinity of the product ion when m is even. We observe ${\mathrm{C}}_3$ loss in the case of ${\mathrm{CsC}}_9^{-}$ clusters. We find an unexpected oscillatory pattern in the kinetic-energy release (KER) spectra of ${\mathrm{C}}_n^{-}$ fragments. The ratio of the width of ${\mathrm{C}}_n^{-}$ to the parent ${\mathrm{CsC}}_n^{-},$ which is a measure of the KER in the center-of-mass (c.m.) frame, shows even-odd oscillation, with the ratio being larger when n is even than when n is odd. The oscillatory pattern is correlated with differences in fragmentation pathways accessed in the Franck-Condon region. Applying the reflection method with model potentials for two different fragmentation paths, we find that the KER in the c.m. frame oscillates if an ion-pair formation pathway is preferred for clusters of even n.

We study the optimization of evaporative cooling in trapped bosonic atoms on the basis of quantum kinetic theory of a Bose gas. The optimized cooling trajectory for ${}^{87}\mathrm{Rb}$ atoms indicates that the acceleration of evaporative cooling around the transition point of Bose-Einstein condensation is very effective against loss of trapped atoms caused by three-body recombination. The number of condensed atoms is largely enhanced by the optimization, more than two orders of magnitude in our present calculation using relevant experimental parameters, as compared with the typical value given by the conventional evaporative cooling where the frequency of radio-frequency magnetic field is swept exponentially. In addition to this optimized cooling, it is also shown that highly efficient evaporative cooling can be achieved by an initial exponential and then a rapid linear sweep of frequency.

We investigate in detail the role of a reservoir concerning the squeezing effect in a driven coupled-oscillator system. In our model, a harmonic oscillator (single cavity mode) is coupled to a two-state oscillator (two-level atom) driven by a classical field. The oscillators are coupled to their respective reservoirs, by which the oscillators are damped. The degree of squeezing in the short-time limit is found to be independent of the damping rate of the harmonic oscillator in a perturbative regime. More remarkably, the harmonic oscillator, which is in a coherent state in the absence of its reservoir, gets squeezed in the steady state when it is coupled to the reservoir. The reservoir assumes two competing roles of assisting and suppressing the squeezing effect induced by the nonlinear interaction of the coupled oscillators. As a result, the squeezing effect is increased to some extent with the damping rate of the harmonic oscillator. In addition, the “matching condition” for the optimal squeezing is obtained such that the pumping field intensity should be inversely proportional to the damping rate.

In the field of atom optics, the basis of many experiments is a two-level atom coupled to a light field. The evolution of this system is governed by a master equation. The irreversible components of this master equation describe the spontaneous emission of photons from the atom. For many applications, it is necessary to minimize the effect of this irreversible evolution. This can be achieved by having a far detuned light field. The drawback of this regime is that making the detuning very large makes the time step required to solve the master equation very small, much smaller than the time scale of any significant evolution. This makes the problem very numerically intensive. For this reason, approximations are used to simulate the master equation, which are more numerically tractable to solve. This paper analyzes four approximations: The standard adiabatic approximation, a more sophisticated adiabatic approximation (not used before), a secular approximation, and a fully quantum dressed-state approximation. The advantages and disadvantages of each are investigated with respect to accuracy, complexity, and the resources required to simulate. In a parameter regime of particular experimental interest, only the sophisticated adiabatic and dressed-state approximations agree well with the exact evolution.

We generated orbital angular momentum in atoms with a spin degree of freedom and coherently transferred it to a light field, which resulted in the generation of a Laguerre-Gaussian (LG) beam. In this method, atoms obtain orbital angular momentum through Larmor precession around the quadrupole field. Successive operations of quadrupole and homogeneous magnetic fields lead to a change of sign in the LG beam or even generation of superposition states of the LG beam with different indexes in real time. Possible applications to control orbital angular momentum of arbitrary photons are also discussed.