Ce travail de thèse présente une étude numérique et théorique de l’influence des effets coopératifs sur la localisation de la lumière dans des vapeurs atomiques, suivie d’une étude expérimentale de ces effets coopératifs dans le régime de diffusion multiple dans des nuages d’atomes froids dilués. Le premier chapitre décrit le modèle que nous utilisons, basé sur l’Hamiltonien effectif d’interaction matière rayonnement, afin d’étudier numériquement la localisation de la lumière et les effets coopératifs. Nous discutons également des différences fondamentales existant entre la situation réelle où la lumière est assimilée à une onde vectorielle et l’approximation scalaire plus facile à traiter analytiquement. Le deuxième chapitre se concentre sur la présentation des résultats numériques complétée d’une comparaison systématique entre les cas scalaire et vectoriel. Nous remarquons dans cette partie que l’approximation scalaire, valable dans la limite des milieux spatialement dilués, présente des différences drastiques avec le cas vectoriel lorsque nous considérons des milieux spatialement denses. Nous n’observons pas également d’indications suffisantes nous permettant de discriminer le fait que les effets coopératifs ne soient pas à la base des mécanismes de localisation de la lumière. Dans la dernière partie nous nous intéressons expérimentalement aux signatures des effets coopératifs dans le régime de diffusion multiple en confrontant à nos résultats expérimentaux plusieurs approches théoriques tenant compte ou pas des effets d’interférences. / In this thesis we present a numerical and theoretical study of the interplay between cooperative effects and light localization in atomic vapour, completed by an experimental study of these cooperative effects for dilute cold atom clouds in the multiple scattering regime. The first chapter describes the model we use, based on the light matter effective Hamiltonian, in order to investigate numerically light localization and cooperative effects. We also discuss the fundamental differences existing between the real situation where light is considered as a vector wave and its scalar approximation easier to treat analytically. The second chapter focuses on the numerical results where we compare systematically the scalar and the vector cases. We show that the scalar approximation, valid for spatially dilute systems, leads to drastic differences compared to the vector case when we consider spatially dense clouds. We also do not observe sufficient proofs to establish that cooperative effects are not at the origin of light localization mechanisms. In the last chapter we investigate experimentally the signatures of cooperative effects in the multiple scattering regime, comparing our results to several theoretical approaches taking or not into account interference effects related to the wave nature of light.

Made available in DSpace on 2017-07-21T19:26:00Z (GMT). No. of bitstreams: 1 JADERSANTOS.pdf: 1951823 bytes, checksum: db75a73fc3676656399742b18f6eeda8 (MD5) Previous issue date: 2011-03-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The Dicke model describes a system that contain a group of atoms coupled to a mode of electromagnetic field. One of the feature of this model is the present of second order quantum phase transition. In this work our main goal is to study the quantum phase transition present in the Dicke model through a mechanical probe. We consider that one of the mirrors in a optical cavity has the freedom to move under the effect of linear restoring force. In this conditions, the mirror couples to the cavity field via pressure radiation interaction. In the thermodynamic limit, we found that the moving mirror decouples from the cavity while in the super radiant phase it suffers the action of a resulting classical force. A remarkable feature is that the entropy of the mirror is not dynamically changed in any phase when the thermodynamic limit is taken. Consequently, the mechanical system will work as a probe to study the critical reservoir namely the Dicke system. / O modelo de Dicke descreve um sistema contendo um conjunto de átomos acoplados a um modo do campo eletromagnético. Uma das características desse modelo é que ele exibe uma transição de fase quântica de segunda ordem. Neste trabalho tivemos como principal objetivo estudar a transição de fase quântica presente nesse modelo através de uma sonda mecânica. Consideramos que um dos espelhos da cavidade óptica tem liberdade para mover-se sob efeito de uma força restauradora linear. Nessas condições, o espelho livre se acopla, via interação de pressão de radiação, com o campo presente na cavidade. No limite termodinâmico observamos que na fase normal o espelho permanecerá desacoplado da cavidade, enquanto que na fase super-radiante o espelho sofre a ação de uma força clássica resultante. Uma característica importante é que a entropia do espelho não se altera dinamicamente em nenhuma das fases, quando no regime termodinâmico. Desse modo, o sistema mecânico funciona como uma sonda para estudar o reservatório (modelo de Dicke).

Submitted by Vasti Diniz (vastijpa@hotmail.com) on 2017-09-13T14:26:30Z No. of bitstreams: 1 arquivototal.pdf: 2274734 bytes, checksum: 20f744b4f2279525b9a574a0a0de7838 (MD5) / Made available in DSpace on 2017-09-13T14:26:30Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 2274734 bytes, checksum: 20f744b4f2279525b9a574a0a0de7838 (MD5) Previous issue date: 2017-02-22 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / In this thesis we deal with G odel-type Universes in the context of modi ed gravity, in particular, Chern-Simons modi ed gravity and Brans-Dicke theory with cosmological constant (BD- ). The G odel-type metrics have been intensively discussed in the General Relativity (GR) over years. It is known that such a metrics present Closed Time-like Curves (CTC's), in other words, the G odel-type metrics are themselves an example of the causality violation. Our goal is verify the consistency of the G odel-type metrics within the Chern-Simons modi ed gravity in both: non-dynamical and dynamical formulations. In the non-dynamical framework, we show that is possible a vacuum solution in contrast to GR. Another essentially new result that we get is the presence of causal solutions for a well-motivated matter source, in general, the solutions have no analogue in GR. Moreover, the vacuum solution represents the limiting case separating the completely causal and non-causal regions, such a property re ects the topological features of the Chern-Simons theory. The primordial distinguishing feature between the Chern-Simons modi ed gravity and GR solutions is the presence of the breaking Lorentz symmetry. It turns out this breaking opens up a range of new solutions. We show that the non-trivial Chern-Simons solutions in the non-dynamical framework is accompanied by rst-order corrections of the Lorentz-violating parameter. Furthermore, in the dynamical framework the geometric parameters are also a ected by second-order corrections of the Lorentzviolating parameter. We also investigated the G odel-type metrics in BD- model. We obtain a vacuum solution which is completely causal, m2 = 4!2, where for ~! ! 1 one recovers the GR with a scalar eld and cosmological constant. It is worth calling attention to the role of the cosmological constant that is fundamental in this context. / Nesta tese tratamos os Universos tipo Code' no contexto da gravidade modificada, em particular, na gravidade modificada de Chern-Simons e na teoria de Brans-Dicke com constante cosmolOgica (BD-A). As metricas tipo Code' vem sendo intensamente discuti­das na Relatividade Geral (RG) ao longo dos anon. Sabe-se que tail metricas apresentam Curvas tipo Tempo Fechadas (CTC's), ou seja, as prOprias metricas tipo Code' sao um exemplo da violagao de causalidade. Nosso objetivo é verificar a consistencia das metricas do tipo Code' dentro da gravidade modificada de Chern-Simons em ambas as formula-goes: nao dinamica e dinamica. Na formulagao nao-dinamica, mostramos que é possivel uma solugao de vacuo diferentemente da RG. Outro resultado essencialmente novo que obtemos é a presenga de solugoes causais para uma fonte de materia bem motivada, em geral, as solugoes nao tem analog° na RG. Alem disso, a solugao de vacuo representa o caso limite que separa as regioes completamente causal e nao causal, tal propriedade re­flete as caracteristicas topolOgicas da teoria de Chern-Simons. A caracteristica que difere fundamentalmente as solugoes da gravidade modificada de Chern-Simons e as da RG é a presenga da quebra da simetria de Lorentz. Acontece que essa quebra abre um leque de novas solugoes. Mostramos que as solugoes nao triviais de Chern-Simons na formulagao nao dinamica sao acompanhadas por corregoes de primeira ordem do parametro de viola­gao de Lorentz. Alem disso, na formulagao dinamica os parametros geometricos tambem sao afetados por corregoes de segunda ordem do parametro de violagao de Lorentz. Investigamos tambem as metricas tipo Code' no modelo BD-A. Obtemos uma solugao de vacuo completamente causal, m2 = 4w2, onde para cD -+ oo recupera-se a GR com um campo escalar e constante cosmolOgica. Vale a pena chamar a atengao para o papel da constante cosmolOgica que é fundamental neste contexto.

Submitted by Vasti Diniz (vastijpa@hotmail.com) on 2017-09-19T13:39:47Z No. of bitstreams: 1 arquivototal.pdf: 1029692 bytes, checksum: e88e69e5c9a3cffdaf665a4b3a2d8d85 (MD5) / Made available in DSpace on 2017-09-19T13:39:47Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1029692 bytes, checksum: e88e69e5c9a3cffdaf665a4b3a2d8d85 (MD5) Previous issue date: 2013-06-28 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / We show that the theory of General Relativity can be entirely formulated in the language of the integrable Weyl geometry. We develop the concept of Weyl frames and state the fact that they are completely equivalent as far as geodesic motion is concerned. In the case of General Relativity, we build an action that is manifestly invariant with respect to Weyl transformations. In this scenario, the gravitational field is described by a combination of both the metric and a geometrical scalar field. We illustrate this point by examining how distinct geometrical and physical pictures of the same phenomena may arise in different frames for the particular case of conformally flat spacetimes. Besides, we show that our choice of Weyl geometry for describing the space-time of General Relativity completely agrees with Poincare ideas that the geometry of space was merely a convention and that no geometry is more correct than any other, only more convenient. On the other hand, we consider the Brans-Dicke gravitational theory as a point of departure for constructing a geometric scalar-field theory. In this approach we apply the Palatini variational method to the Brans-Dicke action. We then are naturally led to conclude that space-time has the geometrical structure of a Weyl integrable manifold. We briefly examine some features of this scalar-tensor theory in which Brans-Dicke scalar field now plays the role of a geometrical field. / A gravitagao tern lido atribuida, desde a aparigao da relatividade geral, a curvatura do espago­tempo. A linguagem geometrodinamica por esta teoria introduzida, representa uma ferra­menta conveniente para predizer o comportamento da materia. Partindo da ideia proposta por Poincare de que a geometria do espago é apenas uma convengao, afirmando que nenhuma geometria é mais correta que outra, mas mais conveniente, mostramos como certas teorias da gravitagao, ern particular a teoria geral da relatividade, assim como a teoria de Brans-Dicke, podem ser completamente reformuladas numa geometria que é uma generalizagao da geometria riemanniana: a geometria de Weyl integravel. Corn esta escolha da linguagem matematica, o movimento das particulas e raios de luz correspondem a geodesicas weylia­nas, as quais satisfazem uma nova classe de invariancia, a invariancia por transformagoes de Weyl. Estas transformagoes permitem definir os chamados referenciais de Weyl e, no caso da teoria da gravitagao criada por Einstein, recupera-la na sua formulagao riemanniana, num gauge particular. Por outro lado, esta modificagao na dinamica dos objetos traz uma nova percepgao dos fenomenos fisicos que tentaremos explorar.

Submitted by Sérgio Mittmann dos Santos (smittmanns@gmail.com) on 2018-04-13T23:20:37Z No. of bitstreams: 1 Tese_SMdS.pdf: 14966593 bytes, checksum: 50aeb1b3bc772ed3ff21708296193489 (MD5) / Rejected by Pamella Benevides Gonçalves null (pamella@feg.unesp.br), reason: Solicitamos que realize correções na submissão seguindo as orientações abaixo: É necessário revisar a formatação das referências seguindo a ABNT 6023:2003, por exemplo, o que ocorre em sua Tese é a ausência da indicação de autoria segundo as normas, abaixo orientação da ABNT. entre outros elementos. 8.1.1 Autor pessoal Indica(m)-se o(s) autor(es), de modo geral, pelo último sobrenome, em maiúsculas, seguido do(s) prenome(s) e outros sobrenomes, abreviado(s) ou não. Recomenda-se, tanto quanto possível, o mesmo padrão para abreviação de nomes e sobrenomes, usados na mesma lista de referências. Os nomes devem ser separados por ponto-e-vírgula, seguido de espaço. Sobre a elaboração das referencias e citações favor solicitar orientação com a bibliotecária Juciene (juciene@feg.unesp.br) Agradecemos a compreensão. on 2018-04-16T18:47:09Z (GMT) / Submitted by Sérgio Mittmann dos Santos (smittmanns@gmail.com) on 2018-04-18T17:12:53Z No. of bitstreams: 1 Tese_SMdS_2.pdf: 4371571 bytes, checksum: cd4208377d9640590e86974e7a28bc7c (MD5) / Approved for entry into archive by Pamella Benevides Gonçalves null (pamella@feg.unesp.br) on 2018-04-19T19:05:30Z (GMT) No. of bitstreams: 1 santos_sm_dr_guara.pdf: 4371571 bytes, checksum: cd4208377d9640590e86974e7a28bc7c (MD5) / Made available in DSpace on 2018-04-19T19:05:30Z (GMT). No. of bitstreams: 1 santos_sm_dr_guara.pdf: 4371571 bytes, checksum: cd4208377d9640590e86974e7a28bc7c (MD5) Previous issue date: 2018-02-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A partir da teoria da gravitação de Brans-Dicke, são obtidas soluções exatas para as cordas cósmicas girantes. As soluções são para cordas retas, que preservam a simetria de Lorentz ao longo do eixo longitudinal de simetria, e para as não retas, com simetria aproximadamente cilíndrica e que violam a simetria de Lorentz. Essas soluções permitem verificar se os espaços-tempos das cordas são regulares ou apresentam singularidades. Além disso, a possibilidade de que as cordas sejam fontes de curvas tipo-tempo fechadas também é analisada. Exclusivamente para as cordas retas, é verificado se essas se mantiveram estáveis após as suas eventuais formações, e se uma escolha adequada para as constantes de integração das soluções impede a existência das curvas tipo-tempo fechadas. Desde a década de 1930, as observações mostram que as velocidades tangenciais das estrelas das galáxias têm um comportamento que contraria o que é previsto quando se considera somente a presença de matéria visível: à medida que as distâncias até os centros das galáxias aumentam, as velocidades também aumentam, até que começam a tender para valores aproximadamente constantes. A razão para esse fenômeno ainda está sob debate. Por enquanto, é justificado pela presença de matéria escura nos halos das galáxias, mas a própria matéria escura ainda não é bem entendida. Em 1980, para 21 galáxias do tipo Sc, as observações mostraram que esse crescimento das velocidades até atingirem os valores constantes ocorre quando as distâncias crescem por 2 a 3 ordens de grandeza. Com as soluções da teoria de Brans-Dicke para as cordas não retas, é proposto um espaço-tempo com a mesma simetria aproximadamente cilíndrica, que descreve adequadamente esse comportamento nas velocidades das estrelas daquelas 21 galáxias / From the Brans-Dicke theory of gravitation, exact solutions are obtained for the spinning cosmic strings. The solutions are for straight strings, which preserve the Lorentz symmetry along the longitudinal axis of symmetry, and for the non-straight strings, with nearly cylindrical symmetry and which violate the Lorentz symmetry. These solutions allow us to verify if the spacetimes of the strings are regular or have singularities. In addition, the possibility that the strings are sources of closed timelike curves is also analyzed. Only for the straight strings, it is verified if these have remained stable after their eventual formations, and if a suitable choice for the integration constants of the solutions prevents the existence of the closed timelike curves. Since the 1930s, observations have shown that the tangential velocities of galaxies’ stars have a behavior that goes against what is predicted when considering only the presence of visible matter: as distances to the centers of galaxies increase, velocities also increase until they begin to tend to approximately constant values. The reason for this phenomenon is still under discussion. For now, it is justified by the presence of dark matter in the halos of galaxies, but the dark matter itself is still not well understood. In 1980, for 21 Sc-type galaxies, observations showed that such velocities growth until reaching constant values occurs when distances grow by 2 to 3 orders of magnitude. With the solutions of the Brans-Dicke theory for the non-straight strings, a spacetime with the same nearly cylindrical symmetry is proposed, which adequately describes this behavior in the velocities of the stars of those 21 galaxies

En Electrodynamique Quantique en Cavité (" Cavity QED "), l'interaction entre la transition atomique et le champ de la cavité est quantifiée par la fréquence de Rabi du vide. L'expression analogue " circuit QED " a été introduite pour certains circuits supraconducteurs contenant des Jonctions Josephson, parce qu'ils pouvaient se comporter comme des atomes artificiels couplés au mode bosonique du résonateur. Dans le régime où la fréquence de Rabi du vide est comparable à la fréquence de transition du système à deux niveaux, des transitions de phases quantiques superradiantes ont été prédites pour le fondamental du système, par exemple dans le cadre du modèle de Dicke. Des réalisations possibles du modèle de Dicke par des systèmes de circuit QED sont étudiées ici théoriquement dans les cas de couplage capacitif ou inductif. Prédictions et contraintes sont analysées pour l'obtention d'une transition de phase quantique, avec un vide deux fois dégénéré au-dessus d'un point critique quantique. La robustesse et la protection de la dégénérescence du vide dans le régime de couplage ultrafort sont étudiées, et conduisent à de possibles applications en Information Quantique avec des réseaux de plusieurs résonateurs. Finalement, un modèle de Dicke généralisé avec une phase doublement superradiante et un vide quatre fois dégénéré est proposé.

Mit dieser Arbeit wird ein Beitrag zur Weiterentwicklung der akustischen lasermesstechnischen Verfahren zur Ermittlung von mechanischen und elastischen Eigenschaften von mikromechanischen Mehrschichtsystemen geleistet. Zu diesen Eigenschaften zählen das E-Modul, die Dichte, die Dicke sowie die Poissonzahl. Die meisten akustischen lasermesstechnischen Verfahren basieren auf der optischen Erzeugung von breitbandigen akustischen Wellen in einem Schichtsystem und der Ermittlung der Geschwindigkeit dieser Wellen durch eine Zweipunkte-Messung. Durch die spektrale Analyse des Wellenzuges an den zwei Messpunkten wird die Dispersionskurve als Relation zwischen Geschwindigkeit und Frequenz der Welle ermittelt. Ausgehend von geeigneten Modellen des Schichtsystems werden die mechanischen und elastischen Eigenschaften des Schichtsystems so lange variiert, bis eine Übereinstimmung zwischen modellierter und gemessener Dispersionskurve stattfindet. In der vorliegenden Arbeit wurde die optische Erzeugung der akustischen Wellen schmalbandig realisiert. Dadurch wurde die Zweipunkte-Messung durch eine Einpunktmessung ersetzt und damit die Ungenauigkeit der Wegmessung eliminiert. Außerdem wird die spektrale Analyse des Wellenzuges auf eine einfachere FFT-Berechnung reduziert. Bei der Modellierung wurde ein bestehendes Randelementenmodell auf eine unbegrenzte Zahl von Schichten innerhalb vom Schichtsystem erweitert. In diesem erweiterten Modell ist es möglich, beliebige Kombinationen von Eigenschaften unterschiedlicher Schichten gleichzeitig zu ermitteln. Außerdem können Mehrschichtsysteme mit beliebiger kristalliner Orientierung der Schichten untersucht werden. Um die Grenzen des entwickelten Verfahrens zu zeigen, wurden verschiedene Mehrschichtsysteme untersucht. Darunter ist z.B. ein Schichtsystem mit einer hexagonal angeordneten AIN-Schicht. Weiterhin wurde ein Schichtsystem mit einem sehr niedrigen messbaren Dispersionseffekt von weniger als 1% (polykristalline Siliziumschicht auf einem Siliziumsubstrat) untersucht. Außerdem wurde ein Schichtsystem mit einer Silizium-Germanium-Mischschicht untersucht und aus den Parametern E-Modul, Dichte und Poissonzahl die Germaniumkonzentration in der Schicht ermittelt. / This thesis represents a further development of the existing laser acoustic techniques for the measurement of mechanical and elastic properties of micromechanical multi layer systems. Most of the existing laser acoustic techniques are based on the optothermal generation of broadband surface acoustic waves in a layer system. To measure the velocity of the generated waves, a two points measurement of the wave train is typically performed. From the analysis of the spectrum of the wave trains at the two points, a dispersion curve (velocity of the surface acoustic wave against frequency) can be determined experimentally for the layer system. The dispersion relation is also determined through an appropriate model for the layer system. When the mechanical and elastic properties of the layer system are changed in the model, until the modeled and the experimental dispersion curves match in a least square sense, then the mechanical and elastic properties are found. In the present thesis, the optothermal generation of the surface acoustic waves is performed in a narrowband setup. A second point for the measurement of the acoustic wave train is not needed. The use of only one measurement point instead of two ameliorates the accuracy of the measurement (no distance measurement between two points is needed). Further, no spectrum analysis of the wave train is replaced with a simpler FFT. From the frequency of the wave train and the given wavelength from the generation mask, the velocity for each frequency can be determined easily. For the modeling of the dispersion curve, an existing BEM model is expanded to consider an unlimited number of layers. In this new model, any combination of properties can be determined for layers and substrates with any cristalline orientation given. The developed method is used to determine the properties of many challenging multi layer systems.One layer system has an AIN layer with a hexagonal structure. Another layer system has a very low dispersion effect of less than 1% velocity difference over the frequency range (polycristalline silicon on a silicon substrate). Another layer system contains a Silicon-Germanium layer. From the measured properties Young's modules, density and Poisson ration of this layer, the germanium concentration is determined.

I examine the observational effects of a light scalar field with a scalar coupling to masses and a pseudoscalar coupling to light and particle spins. The pseudoscalar coupling to light induces a coupling to atomic spins both by inducing a coupling to particle spins directly, and by interactions with electromagnetic fields in the atom. Experiments measuring the interaction of spins to the gradient of the field are the only known way to measure the strength of the interaction with spins. However, limits on the interaction with light derived from these experiments are barely competitive with the separate astronomical limits on the scalar interaction and the interaction with light. Assuming a low mass of the field, as would be the case if the field acts as quintessence, the polarization rotation of the CMB provides a much tighter limit on the product of the pseudoscalar and scalar interaction strengths.

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No description available.