No description available.

Dans les année récentes, les systèmes d'atomes froids ont été reconnus comme des outils prometteurs pour réaliser des simulateurs quantiques, ainsi que pour différentes applications en information quantique. Parmi eux notamment la jonction Josephson bosonique, un système de bosons ultrafroids dilués pouvant occuper deux modes, a été employée pour réaliser un interféromètre atomique, qui a permi d'estimer un déphasage avec une précision dépassant la limite classique. Dans cette thèse, nous étudions d'un point de vue théorique la production, la détection et la décohérence d'états intriqués qui peuvent être utilisés pour l'interférométrie de haute précision dans une jonction Josephson bosonique. Parmi ces états quantiques utiles se trouvent les états comprimés et les superpositions macroscopiques d'états cohérents. Dans la première du manuscrit, nous démontrons que les superpositions macroscopiques d'états cohérents peuvent être créées pendant la dynamique qui suit un arrêt soudain du couplage entre les deux modes de la jonction, puis nous étudions des protocoles de détection expérimentale. Il existe inévitablement dans chaque expérience des sources de bruit, les principaux étant le bruit de phase, induit par des fluctuations des énergies des deux modes, et la perte d'atomes. La présence de bruit induit de la décohérence et dégrade les corrélations quantiques des états manipulés. Dans la deuxième partie du manuscrit nous analysons en détail la façon dont les corrélations quantiques utiles des états comprimés et des superpositions macroscopiques sont dégradées par le bruit de phase. Nous montrons que, pour des intensités de bruit modérées, les superpositions d'états cohérents à plusieurs composantes sont des candidats intéressantes pour l'interférométrie de précision. Enfin, nous étudions l'effet de la perte d'atomes sur la formation des superpositions macroscopiques, en montrant comment la décohérence agit sur la matrice densité du système / In recent years, cold atomic systems have been recognized as very promising tools for quantum simulators and for applications in quantum technology. In particular, a Bose Josephson junction (BJJ) - a system of ultracold dilute bosons which can occupy two modes - has been used to realize an atomic interferometer, allowing to estimate a phase shift with a precision beyond the classical limit. In this thesis we study theoretically the production, detection and decoherence of entangled states which can be used for high-precision interferometry in a Bose Josephson junction. Among such useful quantum states are atomic squeezed states and macroscopic superpositions of coherent states. In the first part of the thesis, after demonstrating that macroscopic superpositions of coherent states can be created during the dynamics following a "quench" of the coupling between the two modes of the junction, we study protocols for their experimental detection. In the experiments there are unavoidable sources of noise, the major sources being phase noise, induced by stochastic fluctuations of the energies of the two modes of the BJJ, and particle losses. The presence of noise induces decoherence and degrades the quantum correlations of these states. In the second part of the thesis we analyze in detail how the useful quantum correlations of squeezed states and macroscopic superpositions are degraded by phase noise. We show that for moderate phase noise intensities multicomponent superpositions of coherent states are interesting candidates for high-precision atom interferometry. Finally, we address the effect of atom losses on the formation of macroscopic superpositions, showing how decoherence affects the system density matrix.

This thesis provides a summary of the laser system constructed in the Quantum Degenerate Gases Laboratory for laser cooling and trapping of 85/87Rband 6Li as well as of experiments that have been pursued in our lab to date. The first chapter provides an overview of the experimental focus of the QDG lab. The second and third chapters provide the fundamental theory behind laser cooling and trapping. The fourth chapter provides details of the laser system. The fifth chapter describes an experiment performed on the subject of dual-injection, performed in collaboration with Dr. James Booth of the British Columbia Institute of Technology (BCIT) involving the dual-injection of a single slave amplifier. The last chapter describes the progress made on the experimental setup needed for the study of Feshbach resonances between 85/87Rb and 6Li and the photoassociative formation of molecules.

This thesis provides a summary of the laser system constructed in the Quantum Degenerate Gases Laboratory for laser cooling and trapping of 85/87Rband 6Li as well as of experiments that have been pursued in our lab to date. The first chapter provides an overview of the experimental focus of the QDG lab. The second and third chapters provide the fundamental theory behind laser cooling and trapping. The fourth chapter provides details of the laser system. The fifth chapter describes an experiment performed on the subject of dual-injection, performed in collaboration with Dr. James Booth of the British Columbia Institute of Technology (BCIT) involving the dual-injection of a single slave amplifier. The last chapter describes the progress made on the experimental setup needed for the study of Feshbach resonances between 85/87Rb and 6Li and the photoassociative formation of molecules.

This thesis provides a summary of the laser system constructed in the Quantum Degenerate Gases Laboratory for laser cooling and trapping of 85/87Rband 6Li as well as of experiments that have been pursued in our lab to date. The first chapter provides an overview of the experimental focus of the QDG lab. The second and third chapters provide the fundamental theory behind laser cooling and trapping. The fourth chapter provides details of the laser system. The fifth chapter describes an experiment performed on the subject of dual-injection, performed in collaboration with Dr. James Booth of the British Columbia Institute of Technology (BCIT) involving the dual-injection of a single slave amplifier. The last chapter describes the progress made on the experimental setup needed for the study of Feshbach resonances between 85/87Rb and 6Li and the photoassociative formation of molecules. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

La mécanique quantique a révolutionné la compréhension du monde microscopique depuis son avènement au XXe siècle. Cependant, les propriétés de la matière condensée restent difficiles à étudier en raison d'une puissance de calcul insuffisante pour simuler numériquement les systèmes à N corps. Une approche alternative consiste à piéger des atomes froids dans des réseaux, dont le comportement est analogue à celui des électrons dans un cristal. Ce système modèle, dont les paramètres peuvent être contrôlés, permet de simuler les phénomènes étudiés.La technique usuellement employée pour confiner les atomes ultrafroids dans un réseau consiste à produire une onde stationnaire résultant de l'intérférence entre deux faisceaux contrapropageants. L'originalité du projet dans lequel s'inscrit cette thèse est de générer un potentiel sublongueur d'onde grâce à la modulation des forces de Casimir au voisinage d'une surface nanostructurée. Le confinement des atomes dans un réseau bidimensionnel avec une faible distance intersite (typiquement 50 nm) permettra ainsi de mieux appréhender les propriétés des matériaux, tels que le graphène.Le travail réalisé au cours de mon doctorat s'est ainsi articulé autour de quatre axes. Tout d'abord, le refroidissement d'atomes de Rubidium 87 a été effectué jusqu'à obtenir un condensat de Bose-Einstein. Puis, des simulations numériques ont été réalisées pour mettre en place une nouvelle méthode d'imagerie sublongueur d'onde, s'appuyant sur le couplage différencié des niveaux atomiques avec un double réseau. Ceci permettra d'activer de façon sélective les sites à détecter pour localiser les atomes avec une précision sublongueur d'onde. Un nouveau système d'imagerie a d'ailleurs été développé pour mieux résoudre les images des distributions atomiques. D'autre part, des simulations numériques ont été réalisées pour anticiper les résultats expérimentaux sur le transport adiabatique au voisinage d'une surface. Enfin, dans le cadre de ma convention CIFRE, une nouvelle architecture laser sera présentée, dans le but d'intéragir avec les atomes de potassium 40 qui seront à refroidir dans la suite du projet dans lequel s'inscrit ma thèse. / Quantum mechanics was a revolution for microscopic systems understanding. However, the study of many-body systems remains a challenge because of computation complexity. Ultracold atoms trapped in lattices offer an alternative way to simulate condensed matter properties. Indeed, their behaviour is similar to the one of electrons in crystals.The common approach for generating optical lattices is to make two laser beams interefere so that we can get a stationary wave that reproduces the potential wells of the crystalline structure. In the new ongoing project, the lattices will be produced by modulation of Casimir-Polder forces nearby a nanostructured surface. Ultracold atoms trapped in a 2D lattice with a short lattice spacing (50 nm) will enable a better understanding of material properties (e.g. graphene).The work I have done during my thesis can be split into in four parts. The first one consisted in cooling Rubidium 87 until Bose-Einstein condensate regime. Then, numerical simulations were performed to set up a new subwavelength imaging technique, based on different couplings between atomic levels with a double lattice. This will make it possible to activate the sites selectively, in order to pinpoint the atoms with subwavelength precision. Moreover, a new imaging system was developped to improve the resolution of the atomic cloud images. I did new calculations in order to predict experimental results on adiabatic atomic transport in the near field of a surface. Finally, a new laser architecture was designed in this thesis, as part of CIFRE convention, in order to cool down potassium 40 atoms, which has to be done in the future.

No description available.

Ultracold atoms have been successfully used to study numerous systems, previously unaccessible, but a precise control over the atom number of the sample still remains a challenge. This dissertation describes our progress towards achieving Fock states of atoms. The first three chapters cover the basic physics necessary to understand the techniques we use in our lab to manipulate atoms. We then summarize our experimental results from an earlier setup where we did two experiments. In the first experiment we compare the transport of cold atoms and a Bose Einstein Condensate (BEC) in a periodic potential. We find a critical potential height beyond which the condensate behavior deviates significantly from that of thermal atoms. In the second experiment we study the effect of periodic temporal kicks by a spatially periodic potential on a BEC in a quasi one dimensional trap. We observe a limit on the energy that the system can absorb from the kicks, which we conclude is due to the finite height of the trap rather than quantum effects. The majority of the dissertation discusses our experimental setup designed to produce Fock states. The setup is designed to use the method of laser culling to produce Fock states. We are able to create a BEC and transport it into a glass cell 25 cm away. We tried different innovative methods to reduce vibrations during transport before finally settling to a commercial air bearing translation stage. We create a high confinement one dimensional optical trap using the Hermite Gaussian TEM₀₁ mode of a laser beam. Such a trap gives trapping frequencies comparable to an optical lattice and allows us to create a single one dimensional trap. We creating the TEM₀₁ mode using an appropriate phase object (phase plate) in the path of a TEM₀₀ mode beam. The method for producing the phase plate was very well controlled to obtain a good quality mode. Once the atoms are loaded into this one dimensional trap we can proceed to do laser culling to observe Sub-Poissonian number statistics and eventually create Fock states of few atoms. Finally, we describe a novel method to create a real time tunable optical lattice which would provide us with the ability of spatially resolved single atom detection. The majority of the dissertation discusses our experimental setup designed to produce Fock states. The setup is designed to use the method of laser culling to produce Fock states. We are able to create a BEC and transport it into a glass cell 25 cm away. We tried different innovative methods to reduce vibrations during tr₀ansport before finally settling to a commercial air bearing translation stage. We create a high confinement one dimensional optical trap using the Hermite Gaussian TEM₀₁ mode of a laser beam. Such a trap gives trapping frequencies comparable to an optical lattice and allows us to create a single one dimensional trap. We creating the TEM₀₁ mode using an appropriate phase object (phase plate) in the path of a TEM₀₀ mode beam. The method for producing the phase plate was very well controlled to obtain a good quality mode. Once the atoms are loaded into this one dimensional trap we can proceed to do laser culling to observe Sub-Poissonian number statistics and eventually create Fock states of few atoms. Finally, we describe a novel method to create a real time tunable optical lattice which would provide us with the ability of spatially resolved single atom detection. The majority of the dissertation discusses our experimental setup designed to produce Fock states. The setup is designed to use the method of laser culling to produce Fock states. We are able to create a BEC and transport it into a glass cell 25 cm away. We tried different innovative methods to reduce vibrations during transport before finally settling to a commercial air bearing translation stage. We create a high confinement one dimensional optical trap using the Hermite Gaussian TEM₀₁ mode of a laser beam. Such a trap gives trapping frequencies comparable to an optical lattice and allows us to create a single one dimensional trap. We creating the TEM₀₁ mode using an appropriate phase object (phase plate) in the path of a TEM₀₀ mode beam. The method for producing the phase plate was very well controlled to obtain a good quality mode. Once the atoms are loaded into this one dimensional trap we can proceed to do laser culling to observe Sub-Poissonian number statistics and eventually create Fock states of few atoms. Finally, we describe a novel method to create a real time tunable optical lattice which would provide us with the ability of spatially resolved single atom detection. The majority of the dissertation discusses our experimental setup designed to produce Fock states. The setup is designed to use the method of laser culling to produce Fock states. We are able to create a BEC and transport it into a glass cell 25 cm away. We tried different innovative methods to reduce vibrations during transport before finally settling to a commercial air bearing translation stage. We create a high confinement one dimensional optical trap using the Hermite Gaussian TEM₀₁ mode of a laser beam. Such a trap gives trapping frequencies comparable to an optical lattice and allows us to create a single one dimensional trap. We creating the TEM₀₁ mode using an appropriate phase object (phase plate) in the path of a TEM₀₀ mode beam. The method for producing the phase plate was very well controlled to obtain a good quality mode. Once the atoms are loaded into this one dimensional trap we can proceed to do laser culling to observe Sub-Poissonian number statistics and eventually create Fock states of few atoms. Finally, we describe a novel method to create a real time tunable optical lattice which would provide us with the ability of spatially resolved single atom detection. / text

Cavity quantum electrodynamics (cavity QED) with single atoms and single photons provides a promising route toward scalable quantum information processing (QIP) and computing. A strongly coupled atom-cavity system should act as a universal quantum interface, allowing the generation and storage of quantum information. This thesis describes the realisation of an atom-cavity system used for the production and manipulation of single photons. These photons are shown to exhibit strong sub-Poissonian statistics and indistinguishability, both prerequisites for their use in realistic quantum systems. Further, the ability to control the temporal shape and internal phase of the photons, as they are generated in the cavity, is demonstrated. This high degree of control presents a novel mechanism enabling the creation of arbitrary photonic quantum bits.

Cette thèse aborde deux problèmes ayant trait à la physique des gaz quantiques de basse dimensionnalité. Le premier système étudié est un mélange unidimensionnel de bosons et de fermions sans spin soumis à un potentiel aléatoire. Nous commençons par écrire un Hamiltonien de basse énergie et abordons la question de la localisation du point de vue de l'accrochage des ondes de densité par un désordre faible. En utilisant le Groupe de Renormalisation et une méthode variationnelle dans l'espace des répliques, le diagramme de phase peut être tracé en fonctions de deux paramètres : la force des interactions Bose-Bose et Bose-Fermi. La position et les propriétés des phases dépendent d'un paramètre additionnel, le rapport des vitesses du son de chaque composante du gaz. Quelque soit la valeur de ce rapport nous trouvons trois phases, (i) une phase totalement délocalisée, le liquide de Luttinger à deux composantes, (ii) une phase totalement localisée où les deux composantes sont accrochées par le désordre et (iii) une phase intermédiaire où seuls les fermions sont localisés. Le deuxième système est un gaz de bosons de cœur dur sur un réseau en échelle. Trois paramètres en contrôlent la physique : les amplitudes de saut transverse et longitudinale, et le remplissage. En utilisant plusieurs méthodes analytiques (théorie des perturbations, bosonisation et RG) nous proposons une interprétation de résultats numériques nouveaux obtenus par nos collaborateurs, notamment sur le paramètre de Luttinger du mode symétrique. Nous en déduisons un diagramme de phase en présence de désordre faible. / In this thesis we study two distinct problems related to the physics of quantum gases in one dimension. After writing a low-energy Hamiltonian, we address the question of localization by considering the pinning of density waves by weak disorder. Using the Renormalization Group and a variationnal method in replica space, we find that the phase diagram is adequately plotted as a function of two parameters: the strength of Bose-Bose and Bose-Fermi interactions. The position and properties of the various phases depend on an additional third parameter, the ratio of the phonon velocities of each component of the gas. Whatever the value of this ratio, we identify -- using the Renormalization Group and a variational calculation -- three types of phases, (i) a fully delocalized phase, that is a two-component Luttinger, (ii) a fully localized phase where both components are pinned by disorder and (iii) an intermediate phase where fermions are localized and bosons are superfluid. The second system is a two-leg ladder lattice of hardcore bosons. Three parameters control the physics: transverse and longitudinal tunneling and the filling. Using several analytical methods (perturbation theory, bosonization, RG) we give an interpretation of new numerical results obtained by our collaborators, namely on the Luttinger parameter of the symmetric mode. We deduce a phase diagram for weak disorder.