30 research outputs found
Lifetimes of atoms trapped in an optical lattice in proximity of a surface
We study the lifetime of an atom trapped in an optical vertical lattice in
proximity of a massive surface using a complex scaling approach. We analyze how
the presence of the surface modifies the known lifetimes of Wannier-Stark
states associated to Landau-Zener tunnelling. We also investigate how the
existence of a hypothetical short-distance deviation from Newton's
gravitational law could affect these lifetimes. Our study is relevant in order
to discuss the feasibility of any atomic- interferometry experiment performed
near a surface. Finally, the difficulties encountered in applying the
complex-scaling approach to the atom-surface Casimir-Polder interaction are
addressed.Comment: 10 pages, 8 figure
Laser controlled tunneling in a vertical optical lattice
Raman laser pulses are used to induce coherent tunnelling between
neighbouring sites of a vertical 1D optical lattice. Such tunneling occurs when
the detuning of a probe laser from the atomic transition frequency matches
multiples of the Bloch frequency, allowing for a spectroscopic control of the
coupling between Wannier Stark (WS) states. In particular, we prepare coherent
superpositions of WS states of adjacent sites, and investigate the coherence
time of these superpositions by realizing a spatial interferometer. This scheme
provides a powerful tool for coherent manipulation of external degrees of
freedom of cold atoms, which is a key issue for quantum information processing
Atomic states in optical traps near a planar surface
In this work we discuss the atomic states in a vertical optical lattice in
proximity of a surface. We study the modifications to the ordinary
Wannier-Stark states in presence of a surface and we characterize the energy
shifts produced by the Casimir-Polder interaction between atom and mirror. In
this context, we introduce an effective model describing the finite size of the
atom in order to regularize the energy corrections. In addition, the
modifications to the energy levels due to a hypothetical non-Newtonian
gravitational potential as well as their experimental observability are
investigated.Comment: 12 pages, 8 figure
Dynamical aspects of atom interferometry in an optical lattice in proximity of a surface
The efficiency of an atomic interferometer in proximity of a surface is
discussed. We first study which is the best choice of frequency for a pulse
acting on internal atomic transitions in the same well. Then considering the
modification of atomic energy levels in vicinity of the surface, we propose the
application of two simultaneous Raman lasers and numerically study the
associated interference fringes. We show that the efficiency of the
interferometric scheme is limited by the existence of a residual phase
depending on the atomic path. We propose a symmetric scheme in order to avoid
these contributions. We finally show that the suggested modifications make the
contrast of the interference fringes close to 1 in any configuration, both
close and far from the surface and with one or more initially populated wells.Comment: 8 pages, 9 figure
Étude d'états atomiques à proximité d'une surface massive - Application à l'expérience FORCA-G
This thesis presents the theoretical modeling of the experiment FORCA-G (FORce de CAsimir et Gravitation à courte distance) currently in progress at Paris Observatory. The purpose of this experiment is to measure short-range interactions between an atom and a massive surface. This interaction are of two kind : quantum electrodynamical (Casimir-Polder effect) and gravitationnal. The work presented here was to calculate the atomic states in the context of the experiment such that we can predict results and performances of the experiment. This has allowed to optimize the experimental scheme both for the high-precision measurement of the Casimir-Polder effect and for the search of deviation from the Newton's law of gravity predicted by unification theories.Ce mémoire présente la modélisation théorique de l'expérience FORCA-G (FORce de CAsimir et Gravitation à courte distance) actuellement en cours de développement à l'Observatoire de Paris. L'objet de cette expérience est la mesure des interactions à courte portée entre un atome et une surface massive. Les interactions recherchées sont du type électrodynamique quantique (effet Casimir-Polder) et gravitationnelle. Le travail présenté ici a consisté à calculer les états des atomes dans le contexte de l'expérience afin de prévoir les signaux et les performances de l'expérience. Ceci a permis l'optimisation du schéma expérimental pour la mesure à la fois de l'effet Casimir-Polder à une précision non encore atteinte ainsi que pour la recherche de déviations à la loi de Newton prédites par les théories d'unification
The effects of short-lasting anti-saccade training in Homonymous Hemianopia with and without saccadic adaptation
Homonymous Visual Field Defects (HVFD) are common following stroke and can be highly debilitating for visual perception and higher level cognitive functions such as exploring visual scene or reading a text. Rehabilitation using oculomotor compensatory methods with automatic training over a short duration (similar to 15 days) have been shown as efficient as longer voluntary training methods (>1 month). Here, we propose to evaluate and compare the effect of an original HVFD rehabilitation method based on a single 15 min voluntary anti-saccades task (AS) toward the blind hemifield, with automatic sensorimotor adaptation to increase AS amplitude. In order to distinguish between adaptation and training effect, 14 left- or right-HVFD patients were exposed, 1 month apart, to three trainings, two isolated AS task (Delayed shift and No shift paradigm), and one combined with AS adaptation (Adaptation paradigm). A quality of life questionnaire (NFI-VFQ 25) and functional measurements (reading speed, visual exploration time in pop out and serial tasks) as well as oculomotor measurements were assessed before and after each training. We could not demonstrate significant adaptation at the group level, but we identified a group of nine adapted patients. While AS training itself proved to demonstrate significant functional improvements in the overall patient group, we could also demonstrate in the sub group of adapted patients and specifically following the adaptation training, an increase of saccade amplitude during the reading task (left-HVFD patients) and the Serial exploration task, and improvement of the visual quality of life. We conclude that short-lasting AS training combined with adaptation could be implemented in rehabilitation methods of cognitive dysfunctions following HVFD. Indeed, both voluntary and automatic processes have shown interesting effects on the control of visually guided saccades in different cognitive tasks
A trapped atom interferometer for the measurement of short range forces
International audienc
A trapped atom interferometer for the measurement of short range forces
International audienc