We have produced a Bose-Einstein condensate on a permanent-magnet atom chip based on periodically magnetized videotape. We observe the expansion and dynamics of the condensate in one of the microscopic waveguides close to the surface. The lifetime for atoms to remain trapped near this dielectric material is significantly longer than above a metal surface of the same thickness. These results illustrate the suitability of microscopic permanent-magnet structures for quantum-coherent preparation and manipulation of cold atoms.

Möbius-shell structures and their physical properties have recently received considerable attention experimentally and theoretically. In this work, eigenstates and associated eigenenergies are determined for a quantum-mechanical particle bounded to a Möbius shell including curvature contributions to the kinetic-energy operator. This is done using a parametrization of the Möbius shell–found by minimizing the elastic energy of the full structure–and employing differential-geometry methods. It is shown that inclusion of curvature contributions to the kinetic energy leads to splitting of the otherwise doubly degenerate groundstate and significantly alters the form of the groundstate and excited-state wavefunctions. Hence, we anticipate qualitative changes in the physical properties of Möbius-shell structures due to surface confinement and curvature effects.

A direct derivation is given for the optimal mean fidelity of quantum state estimation of a $d$-dimensional unknown pure state with its $N$ copies given as input, which was first obtained by Hayashi in terms of an infinite set of covariant positive operator valued measures (POVM’s) and by Bruß and Macchiavello establishing a connection to optimal quantum cloning. An explicit condition for POVM measurement operators for optimal estimators is obtained, by which we construct optimal estimators with finite POVMs using exact quadratures on a hypersphere. These finite optimal estimators are not generally universal, where universality means the fidelity is independent of input states. However, any optimal estimator with finite POVM for $M(>N)$ copies is universal if it is used for $N$ copies as input.

Close to converged energies and expectation values for $e^{+}\mathrm{He}\left({}^{3}S^e\right)$ are computed using a ground state wave function consisting of 1500 explicitly correlated Gaussians. The best estimate of the $e^{+}\mathrm{He}\left({}^{3}S^e\right)$ energy was $-2.25059508\text{hartree}$, which has a binding energy of $0.00059508\text{hartree}$ against dissociation into $\mathrm{Ps}+{\mathrm{He}}^{+}$. The $2\gamma$ annihilation rate for the spin doublet state was $5.713\times {10}^9{\mathrm{s}}^{-1}$. The estimated annihilation rate with the core ${\mathrm{He}}^{+}$ electron was $2.506\times {10}^6{\mathrm{s}}^{-1}$. The derived enhancement factor for annihilation with the ${\mathrm{He}}^{+}\left(1s\right)$ core was 2.29, just over 10% smaller than the enhancement factor derived from analyses of annihilation during $e^{+}\text{−}{\mathrm{He}}^{+}$ scattering. The diffuse nature of the wave function, with well separated ${\mathrm{He}}^{+}$ and Ps subsystems, is demonstarted to be on the threshold of satisfying the formal criteria that define a quantum halo state.

The matrix element of a general many-body operator between two Slater determinants is calculated explicitly. For this, a split-and-pair method is introduced that provides a convenient expression of Wick’s theorem and simplifies many-body calculations. The same method is used to determine the generating function of the matrix elements of many-body operators. The split-and-pair method allows also for the diagonalization of the density correlation operators $:n\left(x_1\right)\cdots n\left(x_k\right):$, where $n\left(x\right)={\psi }^{†}\left(x\right)\psi \left(x\right)$ is the density operator. The relation between the split-and-pair method and quantum group theory is clarified.

Young’s double slit interference effects for low incident energy $75.6\mathrm{eV}$ electron impact ionization of ${\mathrm{N}}_2$ are investigated using the distorted-wave impulse approximation (DWIA) for both coplanar symmetric and asymmetric scattering. Although the DWIA does not predict observable interference effects for the coplanar symmetric case, it predicts some strong Young’s double-slit-type interference effects for the highly asymmetric scattering case. These effects are strong enough that they should be experimentally observable if one can make measurements in the backscattering region.

A vector $\mathbf{\rho }$ is introduced in such a manner that the equilibrium rotational distribution function for a general rigid body has a simple quadratic form both from a body-fixed and space-fixed frame of reference. It is shown that when considering nonequilibrium distribution functions, representations employing the components of $\mathbf{\rho }$ generalize more easily than those employing the components of the angular momentum or angular velocity, and lead to forms with greater accuracy. The behavior of $\mathbf{\rho }$ and its relation to the angular momentum of the system is explored in some detail. Comparisons are made with distribution functions generated from molecular dynamics simulations of ${\mathrm{H}}_2{\mathrm{O}}^{+}$ drifting in a helium bath gas under the influence of a uniform electric field.

Photodetachment of the outer shells of the excited ${}^{2}D$ state of ${\mathrm{C}}^{-}$ using an augmented $R$-matrix theoretical methodology has been studied from threshold to $11\mathrm{eV}$. Total and partial cross sections and photoelectron angular distribution asymmetry parameters have been obtained. Excellent agreement between length and velocity formulations is found. In addition, agreement with experiment at $2.076\mathrm{eV}$ for both cross section and $\beta$ for photodetachment to the ground $2s^{2}2p^2{}^{3}P$ state of C is quite good. The results exhibit many examples of Auger decay of shape resonances. Comparison with a previous calculation shows fair agreement except near threshold.

Quantum-mechanical calculations of low-energy collisions of positrons with cubane $\left({\mathrm{C}}_8{\mathrm{H}}_8\right)$ molecules are carried out using a model interaction potential and solving the corresponding scattering equations. The possible presence of low-energy resonances is analyzed in detail and one of them is found to reside largely inside the carbon frame of the cubane. The consequences of this finding are discussed and analyzed.

It is shown that sub-Doppler cooling occurs in an atom-field geometry that can lead to reduced-period optical lattices. Four optical fields are combined to produce a “standing wave” Raman field that drives transitions between two ground state sublevels. In contrast to conventional Sisyphus cooling, sub-Doppler cooling to zero velocity occurs when all fields are polarized in the same direction. Solutions are obtained using both semiclassical and quantum Monte Carlo methods in the case of exact two-photon resonance. The connection of the results with conventional Sisyphus cooling is established using a dressed state basis.

Accurate angularly resolved photodissociation spectra are recorded using electric discharge for preparing the molecular ions, under intense (about ${10}^{14}\mathrm{W}∕{\mathrm{cm}}^2$), short (about 140 fs) laser pulse excitation at 748 nm wavelength. Such experiments are particularly convenient for the interpretation level of theoretical models that neglects ionization-dissociation competition. Abel transformation relates the center-of-mass dissociation probability to the laboratory frame observations. A spatial field average over the laser focus area, together with some statistics on molecular initial rovibrational states, yields to fragments kinetic and angular distributions that are directly comparable to experimental data. Due to small-angle Coulomb explosion, not explicitly taken into account by the model, the theory-versus-experiment confrontation can be quantitatively conducted only for angles exceeding $\pi ∕7$. Very good agreement is obtained for spectra including both single- and two-photon processes that are enhanced at such high laser intensities. The level of accuracy which is reached advocates both for the correct arrangement of the different steps of the theory and for the basic mechanisms (namely, bond softening and vibrational trapping) that are used as interpretative tools.

Field ionization of high Rydberg manifold states $(n=112\text{–}137)$ of rubidium-85 under a rotating electric field has been investigated experimentally and theoretically. Applying a rapidly reversed electric field with a small static perpendicular field to rotate the total electric field around zero, we have observed substantial increase of the fraction of the tunneling field-ionization process and a profound broadening of its ionization peak over a wide range of field strengths with increasing transverse electric field. The observed tunneling field-ionization fraction is almost independent of the slew rate of the applied electric field, and also on the principal quantum number $n$ over the range investigated. To compare with these experimental results, theoretical calculations have been performed with a successive two-step regime. As the first step we calculated the redistributions of magnetic quantum number $m_{\ell }$ and parabolic quantum number $n_1-n_2$ of the states under the rotating electric field. Then the following time evolution of the manifold states with $\mid m_{\ell }\mid ⩽3$ was traced on the Stark map in a coherent as well as an incoherent model. The calculated results are generally in good agreement with the experimental ones. The increase of the tunneling field-ionization fraction under a rotating electric field plays an essential role in achieving the high efficiency in the recently proposed selective-field-ionization scheme for high Rydberg atoms.

The exact ground state of the many-body Schrödinger equation for $N$ bosons on a one-dimensional ring interacting via a pairwise $\delta$-function interaction is presented for up to 50 particles. The solutions are obtained by solving Lieb and Liniger’s system of coupled transcendental equations numerically for finite $N$. The ground-state energies for repulsive and attractive interactions are shown to be smoothly connected at the point of zero interaction strength, implying that the Bethe ansatz can be used also for attractive interactions for all cases studied. For repulsive interactions the exact energies are compared to (i) Lieb and Liniger’s thermodynamic limit solution and (ii) the Tonks-Girardeau gas limit. It is found that the energy of the thermodynamic limit solution can differ substantially from that of the exact solution for finite $N$ when the interaction is weak or when $N$ is small. A simple relation between the Tonks-Girardeau gas limit and the solution for finite interaction strength is revealed. For attractive interactions we find that the true ground-state energy is given to a good approximation by the energy of the system of $N$ attractive bosons on an infinite line, provided the interaction is stronger than the critical interaction strength of mean-field theory.

We propose a method to create superpositions of two macroscopic quantum states of a single-mode microwave cavity field interacting with a superconducting charge qubit. The decoherence of such superpositions can be determined by measuring either the Wigner function of the cavity field or the charge qubit states. Then the quality factor $Q$ of the cavity can be inferred from the decoherence of the superposed states. The proposed method is experimentally realizable within current technology even when the $Q$ value is relatively low and the interaction between the qubit and the cavity field is weak.

We study slow-light propagation dynamics in warm Rb vapor. We present data showing significant pulse reshaping when the bandwidth of the pulses is increased and present a model that qualitatively explains the observed behavior. Our data and modeling emphasize how the Doppler broadening in a warm vapor strongly affects the propagation of high-frequency components and leads to unintuitive features on the transmitted pulse shapes. This has important consequences for applications involving the delay of large-bandwidth pulses.

In a recent paper [S. Bagherinezhad and V. Karimipour, Phys. Rev. A 67, 044302 (2003)], a quantum secret sharing protocol based on reusable Greenberger-Horne-Zeilinger states was proposed. However, in this Comment, it is shown that this protocol is insecure if Eve employs a special strategy to attack.

Reduced-density-matrix-functional theory is applied to open-shell systems. We introduce a spin-restricted formulation by appropriately expressing approximate correlation-energy functionals in terms of spin-dependent occupation numbers and spin-independent natural orbitals. We demonstrate that the additional constraint of total-spin conservation is indispensable for the proper treatment of open-shell systems. The formalism is applied to the first-row open-shell atoms. The obtained ground-state energies are in very good agreement with the exact values as well as other state of the art quantum chemistry calculations.

We propose a scheme that provides large controllable delays for broadband optical pulses. The system is based on the steep dispersion of a coherently driven medium, in which the narrow electromagnetically induced transparency (EIT) band is overcome by using spatial and temporal processing.