1,900 research outputs found
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
LâuniversitĂ© quĂ©bĂ©coise en mutation : entre valorisation du savoir et recherche partenariale
Ce mĂ©moire cherche Ă cerner la recherche universitaire conduite de concert avec lâentreprise privĂ©e : les partenariats de recherche issus de la collaboration universitĂ© â entreprise. AprĂšs avoir dĂ©crit lâĂ©volution rĂ©cente de la recherche Ă lâuniversitĂ© â de sa mission institutionnelle sous lâĂ©gide humboldtienne jusquâĂ la valorisation des savoirs techniques qui donnent corps Ă la « sociĂ©tĂ© et Ă lâĂ©conomie du savoir » â lâanalyse sâemploie Ă mettre au jour les conceptions que sâen font les chercheurs dĂ©sireux de produire des connaissances « utiles » et susceptibles dâavoir des retombĂ©es pratiques. Lâanalyse, qualitative, sâappuie sur une sĂ©rie dâentrevues semi-dirigĂ©es menĂ©es auprĂšs de professeurs actifs en recherche sous cette formule. Sur le plan thĂ©orique, lâĂ©tude proposĂ©e ici se conçoit Ă la lumiĂšre de la thĂ©orie dĂ©veloppĂ©e par JĂŒrgen Habermas dans son ouvrage, devenu classique, La science et la technique comme « idĂ©ologie », publiĂ© voilĂ longtemps, mais dont on dĂ©couvrira la pertinence et lâactualitĂ©.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 professorsâ 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 Habermasianâs perspective which is particularly adapted for studying science and technology development in higher education institutions
RĂ©flexion 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 matĂ©rielles sont caractĂ©risĂ©es par la rĂ©flexion de l'onde de matiĂšre atomique sur le potentiel attractif de Casimir-Polder. Cette rĂ©flexion quantique est dĂ©terminante pour des expĂ©riences telles que GBAR, qui mesurera l'accĂ©lĂ©ration d'un atome d'antihydrogĂšne froid chutant vers une plaque de dĂ©tection. Dans cette thĂšse, le potentiel de Casimir-Polder est calculĂ© Ă partir des propriĂ©tĂ©s de diffusion Ă©lectromagnĂ©tique de l'atome et de la surface. Il s'avĂšre dĂ©pendre de la rĂ©ponse diĂ©lectrique, de l'Ă©paisseur et de la densitĂ© du milieu. Nous montrons que la rĂ©flexion sur ce potentiel est associĂ©e Ă une rupture de l'approximation semiclassique et qu'elle augmente pour des atomes lents et des potentiels faibles. Les transformations de Liouville relient des Ă©quations de Schrödinger avec des potentiels diffĂ©rents mais les mĂȘmes amplitudes de diffusion. L'Ă©quivalence entre la rĂ©flexion quantique sur un puits de potentiel et l'effet tunnel Ă travers une barriĂšre offre de nouvelles perspectives sur le problĂšme. Nous discutons aussi des effets de la gravitĂ© sur le paquet d'onde atomique et de ses consĂ©quences pour les expĂ©riences avec des atomes en chute libre. AssociĂ©e Ă la rĂ©flexion quantique sur un miroir horizontal, la gravitĂ© permet de maintenir des particules dans des Ă©tats Ă longue durĂ©e de vie aux applications prometteuses pour la mĂ©trologie. En particulier, nous proposons un systĂšme pour amĂ©liorer la prĂ©cision de GBAR en rĂ©duisant la dispersion en vitesse des atomes d'antihydrogĂšne
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
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