Long Distance Transport of Ultracold Atoms using a 1D optical lattice

We study the horizontal transport of ultracold atoms over macroscopic distances of up to 20 cm with a moving 1D optical lattice. By using an optical Bessel beam to form the optical lattice, we can achieve nearly homogeneous trapping conditions over the full transport length, which is crucial in order to hold the atoms against gravity for such a wide range. Fast transport velocities of up to 6 m/s (corresponding to about 1100 photon recoils) and accelerations of up to 2600 m/s2 are reached. Even at high velocities the momentum of the atoms is precisely defined with an uncertainty of less than one photon recoil. This allows for construction of an atom catapult with high kinetic energy resolution, which might have applications in novel collision experiments.Comment: 15 pages, 8 figure

Tight polynomial bounds for Loop programs in polynomial space

We consider the following problem: given a program, find tight asymptotic bounds on the values of some variables at the end of the computation (or at any given program point) in terms of its input values. We focus on the case of polynomially-bounded variables, and on a weak programming language for which we have recently shown that tight bounds for polynomially-bounded variables are computable. These bounds are sets of multivariate polynomials. While their computability has been settled, the complexity of this program-analysis problem remained open. In this paper, we show the problem to be PSPACE-complete. The main contribution is a new, space-efficient analysis algorithm. This algorithm is obtained in a few steps. First, we develop an algorithm for univariate bounds, a sub-problem which is already PSPACE-hard. Then, a decision procedure for multivariate bounds is achieved by reducing this problem to the univariate case; this reduction is orthogonal to the solution of the univariate problem and uses observations on the geometry of a set of vectors that represent multivariate bounds. Finally, we transform the univariate-bound algorithm to produce multivariate bounds

Both can be found at the ENTCS Macro Home Page. The Garland Measure and Computational Complexity of Stack Programs

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"Mes respects, Chef" : Petites histoires d'uniformes des personnels pénitentiaires.

"Le port de l'uniforme réglementaire est de rigueur pendant le service. Une tenue propre et correcte contribue à donner du prestige aux agents, elle augmente leur autorité. Une tenue négligée produit un résultat contraire. C'est un point sur lequel on ne saurait trop insister ; les détenus, qui observent et voient tout, ont moins de respect pour l'agent qui néglige sa tenue. C'est une question de dignité personnelle que chacun doit comprendre." Extrait du "Memento du surveillant d'établisseme..