We study the dynamics of two interacting Bose-Einstein condensates, by numerically solving two coupled Gross-Pitaevskii equations at zero temperature. We consider the case of a sudden transfer of atoms between two trapped states with different magnetic moments: the two condensates are initially created with the same density profile, but are trapped into different magnetic potentials, whose minima are vertically displaced by a distance much larger than the initial size of both condensates. Then the two condensates begin to perform collective oscillations, undergoing a complex evolution, characterized by collisions between the two condensates. We investigate the effects of their mutual interaction on the center-of-mass oscillations and on the time evolution of the aspect ratios. Our theoretical analysis provides a useful insight into the recent experimental observations by Maddaloni et al. [Phys. Rev. Lett. 85, 2413 (2000)].

We discuss the possibility of sampling exponential moments of the canonical phase from the s-parametrized phase-space functions. We show that the sampling kernels exist and are well-behaved for any $s>\mathrm{}-1,$ whereas for $s=-1$ the kernels diverge in the origin. In spite of that, we show that the phase-space moments can be sampled with any predefined accuracy from the Q function measured in the double-homodyne scheme with perfect detectors. We discuss the effect of imperfect detection and address sampling schemes using other measurable phase-space functions. Finally, we discuss the problem of sampling the canonical phase distribution itself.

Using a quantum theory for an ensemble of two-level atoms driven by a field in an optical cavity, we show that the spin associated with the atomic ensemble can be squeezed. Two kinds of squeezing are obtained: on the one hand, self-squeezing of the spin when the input field is a coherent one and the atomic ensemble exhibits a large nonlinearity; and on the other hand, squeezing transfer from an incoming squeezed field when the atomic ensemble has a quasilinear behavior.

We study a limited set of optical circuits for creating near maximal polarization entanglement without the usual large vacuum contribution. The optical circuits we consider involve passive interferometers, feed-forward detection, down converters, and squeezers. For input vacuum fields we find that the creation of maximal entanglement using such circuits is impossible when conditioned on two detected auxiliary photons. So far, there have been no experiments with more auxiliary photons. Thus, based on the minimum complexity of the circuits required, if near maximal polarization entanglement is possible it seems unlikely that it will be implemented experimentally with the current resources.

For a given excess energy E above the helium double photoionization (DPI) threshold, just two parameters are necessary to generate any angular set of the fully resolved triply differential cross sections (TDCS) in the case of the two outgoing electrons sharing E equally. It is shown that these parameters, the width and magnitude of the Gaussian ansatz, may be estimated ab initio from the convergent close-coupling (CCC) theory. The CCC calculations have been performed for E in the range of 3–80 eV, allowing for the generation of equal energy-sharing TDCS at arbitrary orientation of the two electrons and polarization of the photons.

The possibility of using the twofold topological degeneracy of spin-1/2 chiral spin liquid states on the torus to construct quantum error-correcting codes is investigated. It is shown that codes constructed using these states on finite periodic lattices do not meet the necessary and sufficient conditions for correcting even a single qubit error with perfect fidelity. However, for large enough lattice sizes, these conditions are approximately satisfied, and the resulting codes may therefore be viewed as approximate quantum error-correcting codes.

Lithium $1s$ photoelectron spectra are reported in high electron and photon energy resolution, with resolved LS term structure of the ${\mathrm{Li}}^{+}$ $1snl$ satellite transitions up to $n=6.\mathrm{}$ Branching ratios and anisotropy parameters of individual lines, determined over the 85–130 eV photon energy range, are compared with R-matrix calculations and with previous works. The high-angular-momentum satellite lines $(L>~2)$ are found to contribute significantly to the $1snl$ satellite cross sections for $n=3\mathrm{}$ and 4, and to become the dominant terms for $n>~5.$ The high-angular-momentum lines exhibit the same photon-energy-dependence as the P-lines, providing experimental evidence that the continuum-continuum state coupling (equivalent to virtual electron collision processes) is responsible for the $L>~1$ terms in the satellite spectrum, in contrast to the electron relaxation (shake-up) mechanism responsible for the S-terms. The angular distribution of the lines in the ${\mathrm{Li}}^{+}$ $1snl,$ $n=2\mathrm{}–6$ groups, determined at 110 eV photon energy, is in good agreement with calculations, showing more isotropic distributions for high-angular-momentum lines.

Two explicit noninteracting kinetic-energy functionals for electronic-structure calculations of molecules are presented. These functionals are obtained by combining kinetic-energy functionals for isolated atoms—generated by means of local-scaling transformations—so as to produce kinetic-energy functionals applicable to the electronic structure of molecules. The adequacy of these functionals was tested by calculating the kinetic energy of a few diatomic molecules. In spite of the fact that computationally these functionals are not harder to apply than the SGA and the generalized-gradient-approximation kinetic-energy functionals, they lead, nevertheless, to a considerably higher accuracy.

We have measured secondary-electron (SE) yield γ induced by 0.5 MeV/u H, He, and Li ions specularly reflected from a SnTe(001) surface. The position-dependent SE production rate is derived from the observed γ. The SE production rate normalized by the observed mean square charge of the reflected ions is almost independent of the atomic number of the projectile ion. This indicates that the surface track potential induced by the projectile ion is negligibly small to affect the SE emission at semiconductor surfaces probably due to rapid relaxation processes.

Complementary to the experimental studies on magic Ba clusters [Rayane et al., Phys. Rev. A 39, 6056 (1989)], it is theoretically found that magic Ba clusters with 13, 19, 23, 26, 29, and 32 atoms have icosahedral or polyicosahedral structures, which are induced by $5d$-electron bonding. As the cluster grows, the average binding energy and mean bond length increase, while the highest occupied–lowest unoccupied molecular-orbital gap decreases. Due to the large atom size of Ba, there are large cavities in magic Ba clusters, where O atoms are trapped in the oxidation, and a small amount of oxygen can sustain the structural skeleton, which results in the fact that Ba suboxide clusters can have the same magic numbers as pure barium clusters, as found in experiment.

We consider a semiconductor microcavity etched into a small post structure in which the polariton modes become quantized. When moderate amounts of excitons are injected, large gain for the lowest confined polariton results from exciton-exciton scattering. We show that gain is sufficient to compensate for typical losses of GaAs structures, and stimulated emission of the confined polariton is eventually achieved at an exciton density below that where Rabi splitting collapses. We study the dependence of the threshold exciton density on post size, polariton loss rate and lattice temperature. We study the polariton statistics, and show that far above threshold, typical transition from super-Poissonian to Poissonian statistics is preserved. Exciton-exciton interaction produces a self-phase modulation, resulting in enhanced frequency noise, and into a net increase of the emission linewidth far above threshold. We show how to produce a number-squeezed state using correlation between frequency and number noise. A numerical example of a realistic structure is also analyzed in detail.

A numerical method is given for affecting nonlinear Schrödinger evolution on an initial wave function, applicable to a wide range of problems, such as time-dependent Hartree, Hartree-Fock, density-functional, and Gross-Pitaevskii theories. The method samples the evolving wave function at Chebyshev quadrature points of a given time interval. This achieves an optimal degree of representation. At these sampling points, an implicit equation, representing an integral Schrödinger equation, is given for the sampled wave function. Principles and application details are described, and several examples and demonstrations of the method and its numerical evaluation on the Gross-Pitaevskii equation for a Bose-Einstein condensate are shown.

We measured the diffusion coefficient of Rb atoms in ${\mathrm{N}}_2$ buffer gas by the constant-gradient spin-echo method. At a temperature of $60°\mathrm{C},$ our measured diffusion coefficient is $D_0=0.159\mathrm{}\hspace{0.5em}{\mathrm{cm}}^2/\mathrm{s},$ which is consistent with values found from polarization decay. We report also the tipping angle dependence of the phase-relaxation time of Rb atoms at high density.

Kinematically complete data and five-body classical trajectory Monte Carlo calculations are presented for fragmentation of ${\mathrm{D}}_2$ by slow ${\mathrm{Xe}}^{26+}$ ions. For strongly perturbing collisions, two types of three-body effects are identified. The largest, due to interactions between the undissociated molecule and the dipole field of the projectile, is compatible with a two-step fragmentation picture. A smaller effect, due to quadrupolelike and higher multipole interactions between the dissociating fragments and the projectile field, extracts internal energy from the exploding molecule and is incompatible with a two-step picture.

The process of quantum tunneling of particles in various physical systems can be effectively controlled even by a weak and slow varying in time electromagnetic signal, especially if to adapt its shape to a particular system. During an under-barrier motion of a particle, such a signal provides a “coherent” assistance of tunneling by the multiquanta absorption resulting in a strong enhancement of the tunneling probability. The semiclassical approach based on trajectories in the complex time is developed for tunneling in a nonstationary field. Enhancement of tunneling occurs when a singularity of the signal coincides in position at the complex time plane with a singularity of the classical Newtonian trajectory of the particle. The developed theory is also applicable to the over-barrier reflection of particles and to reflection of classical waves (electromagnetic, hydrodynamic, etc.) from a spatially-smooth medium.

This paper discusses some effects involving entangled tripartite pure states that are not Schmidt decomposable. A distinctive feature of these effects is that the entanglement is revealed through measurements on only one or two of the three subsystems and furthermore they show up through an interplay between kinematic and dynamic interdependence of subsystems which are not interacting.

We analyze the fidelity of teleportation protocols, as a function of resource entanglement, for three kinds of two-mode oscillator states: states with fixed total photon number, number states entangled at a beam splitter, and the two-mode squeezed vacuum state. We define corresponding teleportation protocols for each case including phase noise to model degraded entanglement of each resource.

Correlations of the type discussed by EPR in their original 1935 paradox for continuous variables exist for the quadrature phase amplitudes of two spatially separated fields. These correlations were first experimentally reported in 1992. We propose to use such EPR beams in quantum cryptography, to transmit with high efficiency messages in such a way that the receiver and sender may later determine whether eavesdropping has occurred. The merit of the new proposal is in the possibility of transmitting a reasonably secure yet predetermined key. This would allow relay of a cryptographic key over long distances in the presence of lossy channels.

How much information about the original state preparation can be extracted from a quantum system which has already been measured? That is, how many independent (noncommunicating) observers can measure the quantum system sequentially and give a nontrivial estimation of the original unknown state? We investigate these questions, and show from a simple example that information about the original preparation is not entirely lost as a result of the measurement-induced collapse of the quantum state, and that an infinite number of independent observers who have no prior knowledge about the initial state can gain partial information about the original preparation of the quantum system.