Cette thèse décrit l'observation expérimentale de l'effet Hong-Ou-Mandel avec une sourceatomique ultra-froide. L’expérience originale réalisée en 1987 par C. K. Hong, Z. Y. Ou et L. Mandel illustre de façon simple une interférence à deux particules explicable uniquement par la mécanique quantique : deux particules bosoniques et indiscernables, arrivant chacune sur une face d'entrée différente d'une lame semi-réfléchissante ressortent ensemble. Cet effet se traduit par une réduction du taux de détection en coïncidence entre les deux voies de sortie quand les particules arrivent simultanément sur la lame. Cette expérience fut originalement réalisée avec des photons et nous rapportons ici la première mise en oeuvre expérimentale avec des particules massives se propageant dans l’espace libre.Après présentation des différentes techniques nécessaires à sa réalisation, nous décrivons cette expérience et analysons les résultats obtenus. En particulier, la réduction du taux de coïncidence est suffisamment forte pour exclure toute interprétation classique ; l'observation de cet effet constitue une brique fondamentale dans le domaine de l’information quantique atomique. / In this thesis, we report the first realisation of the Hong–Ou–Mandel experiment with massive particles in momentum space. This milestone experiment was originally performed in quantum optics: two photons arriving simultaneously at the input ports of a 50:50 beam-splitter always emerge together in one of the output ports. The effect leads to a reduction of coincidence counts which translates into a dip when particles are indistinguishable. We performed the experiment with metastable helium atoms where the specificities of the Micro-Channel-Plate detector allows one to recover the momentum vector of each individual atom.After listing the necessary tools to perform this experiment with atoms, the experimental sequence is discussed and the results are presented. In particular we measured a coincidence count reduction that cannot be explained through any simple classical model. This corresponds to the signature of a two-particle interference, and confirms that our atomic pair source produces beams which have highly correlated populations and are well mode matched. This opens the prospect of testing Bell’s inequalities involving mechanical observables of massive particles, such as momentum, using methods inspired by quantum optics. It also demonstrates a new way to produce and benchmark twin-atom pairs that may be of interest for quantum information processing.

L'helium est le seul materiau qui reste dans son etat liquide sous sa pression de vapeur saturante aux plus basses temperatures. Il est ainsi le systeme ou les proprietes quantiques de l'etat liquide sont les plus evidentes. En effet, l'helium liquide sous sa pression de vapeur saturante au dessous d'une temperature Tl = 2.17 K presente des proprietes macroscopiques spectaculaires qui ont une nature quantique. On dit que l'helium presentant ces proprietes est dans la phase superfluide. De plus, ce systeme a T ~ 0 K presente un condense de Bose-Einstein en mesure du 10% environ des particules. La condensation de Bose-Einstein semble avoir lieu a la meme temperature ou se presente la superfluidite. L'etude de l'helium liquide confine dans des materiaux poreux devrait permettre de mieux comprendre le lien entre superfluidite et condensation de Bose-Einstein, qui, a l'heure actuelle, manque d'une description theorique satisfaisante. La realisation des experiences sur des echantillons d'helium confine est plutot difficile a cause de trois types de difficultes : la caracterisation des materiaux utilise s pour le confinement, la determination de l'etat thermodynamique de l'echantillon d'helium une fois confine et l'utilisation des systemes cryogeniques necessaires a la rea lisation des tres basses temperatures. Il faut d'abord choisir un materiau apte au confinement, c'est a dire avec des pores presentant une distribution de taille etroite autour d'une valeur petite. Il existent desormais des materiaux avec ces caracteristiques et on peut les obtenir avec une caracterisation par isothermes d'adsorption d'azote et diffraction de rayons X. Ensuite, il faut controler l'etat de remplissage du solide poreux. Pour cela, on a introduit une etape experimental supplementaire par rapport aux etudes conduites jusqu'a present: chaque materiau susceptible d'etre utilise pour le confine ment a ete etudie avec la technique des isothermes d'adsorption d'helium. De cette maniere on peut connaitre avec precision la quantite d'helium necessaire au remplissage des echantillon poreux, et on obtient aussi des information sur les phenomenes macroscopiques intervenant pendant le remplissage. En particulier il est possible de detecter la formation d'une phase liquide remplissant les pores, une fois que une ou deux couches d'helium ont ete adsorbees sur les surfaces. Ce phenomene s'appelle condensation capillaire. Cette phase est precisement celle qui nous interesse: une phase liquide confinee. Enfin, la realisation d'experiences aux tres basses temperatures peut entrainer la condensation d'helium liquide dans le tube d'injection. Quand ce phenomene se produit, on ne connait plus l'etat de remplissage des pores. L'utilisation d'une cellule speciale a permis de se passer du capillaire d'injection pour les etudes en fonction de la temperature: il s'agit d'une cellule remplie a conditions ambia ntes avec la correcte quantite d'helium. Deux techniques de diffusion inelastique de neutrons ont ete utilisees pour acceder respectivement a l'energie cinetique moyenne par particule et au spectre des excitations e lementaires. Les mesures d'energie cinetique ont ete menees avec le spectrometre eVS qui est un spectrometre a geometrie inverse utilisant des neutrons epithermiques (E ~ 10 eV). Dans les conditions experimentales, l'energie echangee est E ~ 5 eV et le vecteur d'onde echange est q ~ 100 A-1. Dans ces conditions, il s'avere valable l'approximation d'impulsion qui lie le facteur de structure dynamique (qui est la quantite mesuree) directement a la fonction de distribution des vitesses de l'echantillon. Ces mesures ont ete menees sur un echantillon d'helium confine dans le Vycor et ont montre une augmentation de l'energie cinetique moyenne par particule due au confinement. Ces mesures suggerent aussi que la condensation de Bose-Einstein se verifie a la meme temperature que la superfluidite dans le cas de l'helium confine dans le Vycor. Cela est en contraste avec ce qui avait ete suggere par une autre equipe qui avait conduit des mesures sur un echantillon de Vycor surrempli d'helium. L'effet observe par cette equipe peut etre du a la presence d'helium en volume autour de l'echantillon. Les mesures des excitations elementaires ont ete menees avec les spectrometres MIBEMOL et IN6 qui sont des spectrometres a geometrie directe, sur un echantillon d'helium confine dans des MCM-41. Les MCM-41 sont des materiaux presentant des pores cylindriques dont le diametre peut etre fait varier de facon controlee selon la methode de preparation entre 20 A et 10 0 A. Les MCM-41 choisis ont un diametre d'environ 32 A. Avec le spectrometre MIBEMOL on a etudie les excitations elementaires en fonction du remplissage et on a mis en evidence la correspondance entre le phenomene de condensation capillaire (detecte par isotherme d'adsorption) et la presence d'excitations typiques de l'etat liquide (les excitations appelees phonon-maxon-roton). Avec le spectrometre IN6 on a etudie les excitations elementaires en fonction de la temperature (0.4 < T < 1.8 K). Les excitations elementaires aux grandes longueur d'onde sont perturbees par le confinement d'une maniere compatible avec la geometrie du systeme. En particulier on peut mettre en relation les modes observes avec les fluctuations de densite longitudinales se propageant le long des pores cylindriques des MCM-41. Enfin, on observe aussi une largeur intrinseque (presente a la temperature de 0.4 K) du pic correspondant au ``roton''.

La premiere partie du manuscript concerne l'etude des performances metrologiques d'un etalon secondaire de frequence utilisant les transitions a deux photons du rubidium. La mesure de la frequence absolue de cet etalon est decrite ainsi que ses applications a la spectroscopie de l'hydrogene atomique. La seconde partie concerne le calcul tres precis des niveaux d'energie et des fonctions d'onde de l'ion moeculaire H2+, ainsi que des resonances des especes exotiques ou l'electron est remplace par un muon ou un pion. A partir des fonctions d'onde, les probabilites de transition a deux photons entre niveaux vibrationnels de H2+ sont calculees. Un nouveau shema experimental pour deduire le rapport de la masse du proton a celle de l'electron par spectroscopie de H2+ est propose et discute. Enfin, une nouvelle methode de calcul du probleme coulombien a trois corps en deux dimensions est proposee et appliquee a l'helium.

Radio-frequency microelectromechanical systems (RF~MEMS) are highly miniaturized devices intended to switch, modulate, filter or tune electrical signals from DC to microwave frequencies. The micromachining techniques used to fabricate these components are based on the standard clean-room manufacturing processes for high-volume integrated semiconductor circuits. RF~MEMS switches are characterized by their high isolation, low insertion loss, large bandwidth and by their unparalleled signal linearity. They are relatively simple to control, are very small and have almost zero power consumption. Despite these benefits, RF~MEMS switches are not yet seen in commercial products because of reliability issues, limits in signal power handling and questions in packaging and integration. Also, the actuation voltages are typically too high for electronics applications and require additional drive circuitry. This thesis presents a novel MEMS switch concept based on an S-shaped film actuator, which consists of a thin and flexible membrane rolling between a top and a bottom electrode. The special design makes it possible to have high RF isolation due to the large contact distance in the off-state, while maintaining low operation voltages due to the zipper-like movement of the electrostatic dual-actuator. The switch comprises two separately fabricated parts which allows simple integration even with RF circuits incompatible with certain MEMS fabrication processes. The two parts are assembled by chip or wafer bonding which results in an encapsulated, ready-to-dice package. The thesis discusses the concept of the switch and reports on the successful fabrication and evaluation of prototype devices. Furthermore, this thesis presents research results in wafer-level packaging of (RF) MEMS devices by full-wafer bonding with an adhesive intermediate layer, which is structured before bonding to create defined cavities for housing MEMS devices. This technique has the advantage of simple, robust and low temperature fabrication, and is highly tolerant to surface non-uniformities and particles in the bonding interface. It allows cavities with a height of up to many tens of micrometers to be created directly in the bonding interface. In contrast to conventional wafer-level packaging methods with individual chip-capping, the encapsulation is done using a single wafer-bonding step. The thesis investigates the process parameters for patterned adhesive wafer bonding with benzocyclobutene, describes the fabrication of glass lid packages based on this technique, and introduces a method to create through-wafer electrical interconnections in glass substrates by a two-step etch technique, involving powder-blasting and chemical etching. Also, it discusses a technique of improving the hermetic properties of adhesive bonded structures by additional passivation layers. Finally, it presents a method to substantially improve the bond strength of patterned adhesive bonding by using the solid/liquid phase combination of a patterned polymer layer with a contact-printed thin adhesive film. / QC 20100617

Path integral Monte Carlo (PIMC) is a method suitable for quantum liquid simulations at finite temperature. We present in this thesis a study of PIMC dealing with the theory and algorithms related to it, and then two applications of PIMC to current research problems of quantum fluids in the Bolzmann regime. The first part encompasses a study of the different ingredients of a PIMC code: action, sampling and physical property estimators. Particular attention has been paid to Li-Broughton's higher order approximation to the action. Regarding sampling, several collective movement methods have been derived, including the bisection algorithm, that has been thoroughly tested. We also include a study of estimators for different physical properties, such as, the energy (through the thermodynamic and virial estimators), the pair distribution function, the structure factor, and the momentum distribution. In relation to the momentum distribution, we have developed a novel algorithm for its estimation, the trail method. It surmounts some of the problems exposed by previous approaches, such as the open chain method or McMillan's algorithm.The Richardson extrapolation used within PIMC simulations, is another contribution of this thesis. Up until now, this extrapolation has not been used in this context. We present studies of the energy dependence on the number of "beads", along with the betterment provide by the Richardson extrapolation. Inasmuch as our goal is to perform research of quantum liquids at finite temperature, we have produced a library of codes, written from scratch, that implement most of the features theoretically developed. The most elaborated parts of these codes are included in some of the appendixes.The second part shows two different applications of the algorithms coded. We present results of a PIMC calculation of the momentum distribution of Ne and normal 4He at low temperatures. In the range of temperatures analysed, exchanges can be disregarded and both systems are considered Boltzmann quantum liquids. Their quantum character is well reflected in their momentum distributions witch show clear departures from the classical limit. The PIMC momentum distributions which show clear departures from the classical limit. The PIMC momentum distributions are sampled using the trail method. Kinetic energies of both systems, as a function of temperature and at a fixed density, are also reported. Finally, the solid-liquid neon phase transition along the 35 K isotherm has been characterized.While thermodynamic properties of the solid phase are well known the behaviour of some properties, such as the energy or the dessity, during the trasition presen6 some uncertainties For example, experimental data for the place diagram, which determines solid and liquid boundaries, present sizeable differences. The temperature chosen is high enough so that Bose or Fermi statistics corrections are small, although the system is strongly quantum mechanical. The results obtained show a discontinuity in the kinetic energy during the transition.

No description available.

Divertors are in-vessel, plasma-facing, components in magnetic-confinement fusion reactors. Their main function is to remove the fusion reaction ash (α-particles), unburned fuel, and eroded particles from the reactor, which adversely affect the quality of the plasma. A significant fraction (~15 %) of the total fusion thermal power is removed by the divertor coolant and must, therefore, be recovered at elevated temperature in order to enhance the overall thermal efficiency. Helium is the leading coolant because of its high thermal conductivity, material compatibility, and suitability as a working fluid for power conversion systems using a closed high temperature Brayton cycle. Peak surface heat fluxes on the order of 10 MW/m^2 are anticipated with surface temperatures in the region of 1,200°C to 1,500°C. Recently, several helium-cooled divertor designs have been proposed, including a modular T-tube design and a modular finger configuration with jet impingement cooling from perforated end caps. Design calculations performed using the FLUENT® CFD software package have shown that these designs can accommodate a peak heat load of 10 MW/m^2. Extremely high heat transfer coefficients (~50,000 W/(m^2 K)) were predicted by these calculations. Since these values of heat transfer coefficient are considered to be outside of the experience base for gas-cooled systems, an experimental investigation has been undertaken to validate the results of the numerical simulations. Attention has been focused on the thermal performance of the T-tube and the finger divertor designs. Experimental and numerical investigations have been performed to support both divertor geometries. Excellent agreement has been obtained between the experimental data and model predictions, thereby confirming the predicted performance of the leading helium-cooled divertor designs for near- and long-term magnetic fusion reactor designs. The results of this investigation provide confidence in the ability of state-of-the-art CFD codes to model gas-cooled high heat flux plasma-facing components such as divertors.

With recent advancements in material science, industrial operations are being conducted at higher and higher temperatures. This is apparent in the nuclear industry where a division of the field is working to develop the High Temperature Gas Reactor and the Very High Temperature Gas Reactor concurrently. Both of these facilities will have outlet gas temperatures that are at significantly higher temperatures than the typical water cooled reactor. These increased temperatures provide improved efficiency for the production of hydrogen, provide direct heating for oil refineries, or more efficient electricity generation. As high temperature operations are being developed, instruments capable of measuring the operating parameters must be developed concurrently. Within the gas reactor community there is a need to measure the impurities within the primary coolant. Current devices will not survive the temperature and radiation environments of a nuclear reactor. An instrument is needed to measure the impurities within the coolant while living inside the reactor, where this instrument would measure the amount of the impurity within the coolant. There are many industrial applications that need to measure the ratio of two components, whether it be the amount of particulate in air that is typical to pneumatic pumping, or the liquid to gas ratio in natural gas as it flows through a pipeline. All of the measurements in these applications can be met using a capacitance sensor. Current capacitance sensors are built to operate at ambient temperatures with only one company producing a product that will handle a temperature of up to 400 °C. This maximum operating temperature is much too low to measure the gas characteristics in the High Temperature Gas Reactor. If this measurement technique were to be improved to operate at the expected temperatures, the coolant within the primary loop could be monitored for water leaks in the steam generator, carbon dust buildup entrained in the flow, or used to measure the purity of the coolant itself. This work details the efforts conducted to develop such an instrument. While the concept of designing a capacitance sensor to measure a gas mixture is not unique, the application of using a capacitance sensor within a nuclear reactor is a new application. This application requires the development of an instrument that will survive a high temperature nuclear reactor environment and operate at a sensitivity not found in current applications. To prove this technique, instrument prototypes were built and tested in confined environments and at high temperatures. This work discusses the proof of concept testing and outlines an application in the High Temperature Test Facility to increase the operational understanding of the instrument. This work is the first step toward the ultimate outcome of this work, which is to provide a new tool to the gas reactor community allowing real-time measurements of coolant properties within the core. / Graduation date: 2013

La structure des nucléons et des noyaux a été intensivement étudiée au cours duvingtième siècle au travers de la diffusion élastique d’électrons (mesure des facteurs deforme électromagnétique) et de la diffusion profondément inélastique (mesure des distributionsde partons). Le formalisme des distributions généralisées de partons (GPD)a permis d’unifier les facteurs de forme et les distributions de partons. Ce lien procureune source d’information unique sur la dynamique des partons, telle la distribution desforces nucléaires et de moment orbital au sein des hadrons. L’accès expérimental le plussimple aux GPD est la diffusion Compton profondément virtuelle (DVCS), correspondantà l’électroproduction dure d’un photon réel. Tandis que plusieurs expériences sesont déjà focalisées sur la réaction DVCS sur le nucléon, les expériences sur une ciblenucléaire s’avèrent plus rares. Cette thèse se concentre sur l’étude du canal DVCS cohérentsur l’hélium 4, avec pour objectif l’extraction des parties réelle et imaginaire dufacteur de forme Compton via l’asymétrie de spin du faisceau. / The structure of the nucleons and of the nuclei was actively studied during the twentiethcentury through electron elastic scattering (measuring the electromagnetic formfactors) and deep inelastic electron scattering (measuring the parton distributions). Theformalism of generalized parton distributions (GPD) achieved the unification of the formfactors and the parton distributions. This link gives a source of information about partondynamics, such as the distribution of nuclear forces and orbital momentum insidehadrons. The easiest experimental access to the GPD is the deeply virtual Comptonscattering (DVCS), which corresponds to the hard electroproduction of a real photon.While several experiments focussed on DVCS off the nucleon, only a few experimentsstudied DVCS off a nuclear target. This thesis is dealing with the study of the coherentchannel of DVCS off helium 4, with the aim to extract the real and imaginary parts ofthe Compton form factor thanks to the beam spin asymetry.

O elemento hélio, encontrado principalmente em reservas de gás natural, entra em condensação à temperatura de 4,2K, e é a única substância conhecida que permanece no estado líquido até o zero absoluto. Na fase liquida, o hélio apresenta ainda, em K, outra mudança de fase, onde passa de líquido comum à superfluido, com viscosidade praticamente nula. Estas propriedades conferem ao hélio importantes aplicações. Uma hdas principais aplicações é como agente refrigerante em supercondutores, como por exemplo, no acelerador de partículas LHC, que está sendo construído na fronteira da França com a Suíça, em aparelhos de ressonância magnética, satélites artificiais, etc. Neste trabalho, são apresentados dois modelos matemáticos para a transferência de calor no hélio líquido. O primeiro modelo, considerando apenas movimentos macroscópicos, é derivado com base nas leis constitutivas de Fourier e de Gorter-Mellink. O segundo modelo, baseado nas técnicas de Fremond, inclui movimentos microscópicos e pode ser visto como uma regularização do primeiro modelo. Os dois modelos são governados por equações diferenciais fortemente não lineares resultantes da não linearidade da lei de Gorter-Mellink e da mudança de fase. Ambos os modelos podem ser considerados casos particulares do problema de Stefan de duas fases, sendo que em uma das fases o fluxo de calor é governado pela equação não-linear do problema conhecido como p-laplaciano, com p=4/3. São também apresentadas técnicas para resolver de forma eficiente o problema do p-laplaciano, tanto para valores grandes de p, p>>2, quanto para valores de p próximos à 1, que constituem importantes desafios numéricos. Para tanto são propostos dois métodos iterativos simples, um baseado no método de quase-Newton, com termo de relaxação e, outro através da decomposição de Helmholtz, gerando um sistema de equações cujas matrizes são constantes, o que diminui significativamente o custo computacional. Experimentos numéricos são realizados para testar a eficiência dos modelos numéricos propostos bem como dos algoritmos desenvolvidos para resolver os sistemas de equações algébricas não lineares resultantes das aproximações por elementos finitos. São apresentados resultados de estudos de convergência, mostrando taxas de convergência ótimas ou quase ótimas, comparáveis às das interpolantes. Para o problema com mudança de fase, devido à descontinuidade do gradiente da temperatura sobre a interface que separa as duas fases do hélio líquido, as taxas de convergência não são ótimas. Usando malhas adaptativas, consegue-se taxas ótimas também para o problema com mudança de fase. Usando dados experimentais, encontrados na literatura, para os parâmetros de condutividade térmica, densidade e calor específico, dependentes da temperatura, são também apresentados testes de validação do modelo e exemplos de possíveis aplicações. Nos testes de validação do modelo, compara-se a solução numérica do modelo matemático com resultados experimentais para a temperatura, encontrados na literatura. / The element helium, found mainly in natural gas reserves, condenses at temperature of 4.2K, and is the unique known substance that remains in liquid to absolute zero. In the liquid phase, the helium presents still another phase change in 2.19K, where passes of common liquid to superfluous liquid, with almost zero viscosity. These properties give the helium important applications. One of the major applications is as a coolant in superconductors, such as in the particle accelerator LHC, which is being built in the French border with Switzerland, in magnetic resonance devices, artificial satellites, etc.. In this paper, we present two mathematical models for heat transfer in liquid helium. The first model, considering only macroscopic movements, is derived based on constitutive laws of Fourier and Gorter-Mellink. The second model, based on techniques of Fremond, includes microscopic movements and can be seen as a regularization of the first model. Both models are governed by highly nonlinear differential equations resulting from the nonlinearity of the law of Gorter-Mellink and change of phase. Both models can be considered special cases of the Stefan problem in two phases, with phase one of the heat flux is governed by non-linear equation of the problem known as p-Laplacian, with p = 4/3. We also presented techniques to efficiently solve the problem of p-Laplacian, both for large values of p, p>> 2, and for values of p close to 1, which are major numerical challenges. Are proposed two simple iterative methods, one based on the method of quasi-Newton, with the relaxation term and the other by the Helmholtz decomposition, creating a system of equations whose matrices are constant, which reduces significantly the computational cost. Numerical experiments are conducted to test the efficiency of numerical models proposed and the algorithms developed for solving systems of nonlinear algebraic equations arising from approximations by finite elements. Are also presented results of studies of convergence, showing rates of optimal or near optimal convergence, comparable to that of interpolates. For the problem with phase change, due to the discontinuity of the gradient of temperature on the interface separating the two phases of liquid helium, the rate of convergence is not optimal. Using adaptive mesh, it is also great rates to the problem with change of phase. Using experimental data found in literature, for the parameters of thermal conductivity, density and specific heat, temperature dependent, are also presented for validation testing of the model and examples of possible applications. In tests for validating the model, compared to the numerical solution of the mathematical model with experimental results for the temperature found in literature.