Vortex dynamics of rotating dipolar Bose-Einstein condensates

We study the influence of dipole-dipole interaction on the formation of vortices in a rotating dipolar Bose-Einstein condensate (BEC) of $^{52}$Cr and $^{164}$Dy atoms in quasi two-dimensional geometry. By numerically solving the corresponding time-dependent mean-field Gross-Pitaevskii equation, we show that the dipolar interaction enhances the number of vortices while a repulsive contact interaction increases the stability of the vortices. Further, an ordered vortex lattice of relatively large number of vortices is found in a strongly dipolar BEC.Comment: 15 pages, 10 figures, 1 tabl

New representations for (max,+) automata with applications to performance evaluation and control of discrete event systems

A large class of timed discrete event systems can be modeled by means of (max,+) automata, that is automata with weights in the so-called (max,+) algebra. In this contribution, specific recursive equations over (max,+) and (min,+) algebras are shown to be suitable for describing extremal behaviors of (max,+) automata. Several pertinent performance indicators can be easily derived or approximated from these representations with a low computation complexity. It is also shown how to define inputs which model exogenous influences on their dynamic evolution, and a new approach for the control of (max,+) automata is proposed

Eléments d'évaluation de performances pour les systèmes à événements discrets à travers de nouvelles représentations pour les automates (max,+)

Dans ce papier, on étudie les performances des systèmes à événements discrets modélisés à l\u27aide d\u27automates (max,+). Pour cela, nous proposons des représentations qui permettent aisément d\u27obtenir le temps d\u27exécution maximum ainsi qu\u27un minorant du temps d\u27exécution minimum pour les séquences de longueur n. Une comparaison avec les résultats de la littérature vise à mettre en avant les avantages de l\u27approche proposée à partir de ces représentations

Off-diagonal correlations in a one-dimensional gas of dipolar bosons

We present a quantum Monte Carlo study of the one-body density matrix (OBDM) and the momentum distribution of one-dimensional dipolar bosons, with dipole moments polarized perpendicular to the direction of confinement. We observe that the long-range nature of the dipole interaction has dramatic effects on the off-diagonal correlations: although the dipoles never crystallize, the system goes from a quasi-condensate regime at low interactions to a regime in which quasi-condensation is discarded, in favor of quasi-solidity. For all strengths of the dipolar interaction, the OBDM shows an oscillatory behavior coexisting with an overall algebraic decay; and the momentum distribution shows sharp kinks at the wavevectors of the oscillations, $Q = \pm 2\pi n$ (where $n$ is the atom density), beyond which it is strongly suppressed. This \emph{momentum filtering} effect introduces a characteristic scale in the momentum distribution, which can be arbitrarily squeezed by lowering the atom density. This shows that one-dimensional dipolar Bose gases, realized e.g. by trapped dipolar molecules, show strong signatures of the dipolar interaction in time-of-flight measurements.Comment: 10 pages, 6 figures. v2: fixed a mistake in the comparison with Ref. 9, as well as several typos. Published versio

Localization of a dipolar Bose-Einstein condensate in a bichromatic optical lattice

By numerical simulation and variational analysis of the Gross-Pitaevskii equation we study the localization, with an exponential tail, of a dipolar Bose-Einstein condensate (DBEC) of $^{52}$Cr atoms in a three-dimensional bichromatic optical-lattice (OL) generated by two monochromatic OL of incommensurate wavelengths along three orthogonal directions. For a fixed dipole-dipole interaction, a localized state of a small number of atoms ($\sim 1000$) could be obtained when the short-range interaction is not too attractive or not too repulsive. A phase diagram showing the region of stability of a DBEC with short-range interaction and dipole-dipole interaction is given

Zeeman slowers made simple with permanent magnets in a Halbach configuration

We describe a simple Zeeman slower design using permanent magnets. Contrary to common wire-wound setups no electric power and water cooling are required. In addition, the whole system can be assembled and disassembled at will. The magnetic field is however transverse to the atomic motion and an extra repumper laser is necessary. A Halbach configuration of the magnets produces a high quality magnetic field and no further adjustment is needed. After optimization of the laser parameters, the apparatus produces an intense beam of slow and cold 87Rb atoms. With a typical flux of 1 - 5 \times 10^10 atoms/s at 30 ms^-1, our apparatus efficiently loads a large magneto-optical trap with more than 10^10 atoms in one second, which is an ideal starting point for degenerate quantum gases experiments.Comment: 8+6 pages (article + appendices: calculation details, probe and oven description, pictures), 18 figures, supplementary material (movie, Mathematica programs and technical drawings

New representations for (max,+)-automata with applications to the performance evaluation of discrete event systems

A large class of timed discrete event systems can be modeled thanks to (max,+)-automata, that is automata with weights in the so-called (max,+) algebra. In this contribution, new representations are proposed for (max,+)-automata. Indeed, specific recursive equations over (max,+) and (min,+) algebras are shown to be suitable for describing extremal behaviors of (max,+)-automata. It is underlined that several performance evaluation elements, such as maximum and minimum string execution times, can be easily derived from these representations