Anderson localization of pairs in bichromatic optical lattices

We investigate the formation of bound states made of two interacting atoms moving in a one dimensional (1D) quasi-periodic optical lattice. We derive the quantum phase diagram for Anderson localization of both attractively and repulsively bound pairs. We calculate the pair binding energy and show analytically that its behavior as a function of the interaction strength depends crucially on the nature -extended, multi-fractal, localized- of the single-particle atomic states. Experimental implications of our results are discussed.Comment: final revised version with more explanations, 4 pages, 3 figure

Quantum Reflection of Antihydrogen in the GBAR Experiment

In the GBAR experiment, cold antihydrogen atoms will be left to fall on an annihilation plate with the aim of measuring the gravitational acceleration of antimatter. Here, we study the quantum reflection of these antiatoms due to the Casimir-Polder potential above the plate. We give realistic estimates of the potential and quantum reflection amplitudes, taking into account the specificities of antihydrogen and the optical properties of the plate. We find that quantum reflection is enhanced for weaker potentials, for example above thin slabs, graphene and nanoporous media.Comment: Workshop on Antimatter and Gravity Bern 2013 Proceeding

L’université québécoise en mutation : entre valorisation du savoir et recherche partenariale

Ce mémoire cherche à cerner la recherche universitaire conduite de concert avec l’entreprise privée : les partenariats de recherche issus de la collaboration université – entreprise. Après avoir décrit l’évolution récente de la recherche à l’université — de sa mission institutionnelle sous l’égide humboldtienne jusqu’à la valorisation des savoirs techniques qui donnent corps à la « société et à l’économie du savoir » — l’analyse s’emploie à mettre au jour les conceptions que s’en font les chercheurs désireux de produire des connaissances « utiles » et susceptibles d’avoir des retombées pratiques. L’analyse, qualitative, s’appuie sur une série d’entrevues semi-dirigées menées auprès de professeurs actifs en recherche sous cette formule. Sur le plan théorique, l’étude proposée ici se conçoit à la lumière de la théorie développée par Jürgen Habermas dans son ouvrage, devenu classique, La science et la technique comme « idéologie », publié voilà longtemps, mais dont on découvrira la pertinence et l’actualité.This thesis focuses on the transformation of universities and, more specifically, the impact of their research partnerships with private companies on the role of universities in contemporary Quebec society. To achieve this, the evolution of university research is described: from its integration in the Humboldtian University as an institutional mission, to the valorization of its results in accordance with the discourse emerging from knowledge economy theories. The qualitative analysis is based on semi-directed interviews with professors-researchers experienced in partnership research projects and their designs. These interviews retrace these professors’ daily life as they work in those partnerships. Different topics such as academic freedom, the relationship with the industrial partners and the training of students were discussed. The data collected was analysed from an Habermasian’s perspective which is particularly adapted for studying science and technology development in higher education institutions

Réflexion quantique sur le potentiel de Casimir-Polder

Collisions between ultracold atoms and material surfaces are characterized by the reflection of the atomic matter wave from the attractive Casimir-Polder potential. This quantum reflection is particularly relevant to experiments such as GBAR, which will determine the gravitational acceleration of a cold antihydrogen atom by timing its fall onto a detection plate. In this thesis, the Casimir-Polder potential is computed from the electromagnetic scattering properties of the atom and surface and it is found to depend notably on the dielectric response, thickness and density of the medium. We show that reflection on this potential is associated with a breakdown of the semiclassical approximation and that it is enhanced for slow atoms and weak potentials. Liouville transformations relate Schrödinger equations with different potential landscapes but identical scattering properties. We gain new insights on the problem of quantum reflection on a potential well by mapping it onto an equivalent problem of tunneling through a wall. We also discuss the effect of gravity on the atomic wavepacket and its implications for free fall experiments with atoms. When combined with quantum reflection from a horizontal mirror, gravity can be used to trap particles in long lived states with promising applications for metrology. In particular, we suggest a scheme to improve the precision of the GBAR experiment by reducing the velocity dispersion of the falling atoms.Les collisions entre atomes ultrafroids et surfaces matérielles sont caractérisées par la réflexion de l'onde de matière atomique sur le potentiel attractif de Casimir-Polder. Cette réflexion quantique est déterminante pour des expériences telles que GBAR, qui mesurera l'accélération d'un atome d'antihydrogène froid chutant vers une plaque de détection. Dans cette thèse, le potentiel de Casimir-Polder est calculé à partir des propriétés de diffusion électromagnétique de l'atome et de la surface. Il s'avère dépendre de la réponse diélectrique, de l'épaisseur et de la densité du milieu. Nous montrons que la réflexion sur ce potentiel est associée à une rupture de l'approximation semiclassique et qu'elle augmente pour des atomes lents et des potentiels faibles. Les transformations de Liouville relient des équations de Schrödinger avec des potentiels différents mais les mêmes amplitudes de diffusion. L'équivalence entre la réflexion quantique sur un puits de potentiel et l'effet tunnel à travers une barrière offre de nouvelles perspectives sur le problème. Nous discutons aussi des effets de la gravité sur le paquet d'onde atomique et de ses conséquences pour les expériences avec des atomes en chute libre. Associée à la réflexion quantique sur un miroir horizontal, la gravité permet de maintenir des particules dans des états à longue durée de vie aux applications prometteuses pour la métrologie. En particulier, nous proposons un système pour améliorer la précision de GBAR en réduisant la dispersion en vitesse des atomes d'antihydrogène

Pairing and the structure of the pf-shell N ~ Z nuclei

The influence of the isoscalar and isovector L=0 pairing components of the effective nucleon-nucleon interaction is evaluated for several isobaric chains, in the framework of full pf shell model calculations. We show that the combined effect of both isospin channels of the pairing force is responsible for the appearance of T=1 ground states in N=Z odd-odd nuclei. However, no evidence is found relating them to the Wigner energy. We study the dependence of their contributions to the total energy on the rotational frecuency in the deformed nucleus 48Cr. Both decrease with increasing angular momentum and go to zero at the band termination. Below the backbending their net effect is a reduction of the moment of inertia, more than half of which comes from the proton-neutron channel.Comment: 5 pages, RevTeX, 5 figure

Hong-Ou-Mandel interference on a lattice: symmetries and interactions

We describe the Hong-Ou-Mandel interference of two identical particles evolving on a one-dimensional tight-binding lattice where a potential barrier plays the role of a beam splitter. Careful consideration of the symmetries underlying the two-particle interference effect allows us to reformulate the problem in terms of ordinary wave interference in a Michelson interferometer. This approach is easily generalized to the case where the particles interact, and we compare the resulting analytical predictions for the bunching probability to numerical simulations of the two-particle dynamics