Les gaz atomiques dégénérés représentent des systèmes modèles pour étudier la superfluidité. Ils offrent la possibilité d'explorer la physique en dimensions restreintes, profondémentdifférente par rapport au cas tridimensionnel. Nous disposons d'un gaz de Bose bidimensionnel dégénéré confiné dans un potentiel très anisotrope et dont on peut changer la géométrie dynamiquement. Une déformation contrôlée du piège permet d'exciter les modes collectifs du gaz. Nous avons fait d'abord une analyse en composantes principales du gaz, et nous avons montré que ces dernières coïncident avec les modes de Bogoliubov. Nous avons ensuite effectué une étude détaillée du mode ciseaux, dont nous nous servons pour sonder le caractère superfluide du gaz, en développant une nouvelle technique d'analyse, appelée "analyse de la moyenne locale". Enfin nous avons réalisé un piège en anneau, obtenu à l'intersection d'un piège en forme de bulle et du potentiel optique d'un faisceau qui présente un noeud d'intensité au centre, la "double nappe", et nous proposons différentes protocoles de mise en rotation des atomes dans l'anneau. / Degenerate atomic gases can be a versatile tool to study superfluidity. They also offer the possibility to explore the low-dimensions physics, which is deeply different from the three dimensional case. We prepare a degenerate Bose gas in a very anisotropic trap, dynamically adjustable. A controlled deformation of the trapping potential can excite the collective modes of the trapped cloud. First we perform a « principal components analysis » of the gas and we show that the principal components coincide with the Bogoliubov modes. We then restrain our analysis on the scissors mode, which we use to probe superfluidity of the sample, by introducing a new analysis technique, called « local average analysis ». Finally I will report on the realization of a ring trap, obtained by superposing a double sheet light beam to a bubble trap, and describe the different possibilities we planned to set atoms into rotation.

O objetivo do presente trabalho foi determinar, através de medidas de Ressonância Fluorescente Nuclear (RFN) para o núcelo deformado de 153Eu, a intensidade integrada de ressonâncias localizadas de dipolo associadas a modos de movimento como o modo tesoura Ml (ressonâncias anãs). Foi utilizado o feixe de elétrons do acelerador Dynamitron da Universidade de Stuttgart (Eo = 4,3 MeV) e detetores de Ge(HP) e Ge(Li) de alta resolução para a obtenção de informações detalhadas acerca das energias de excitação, larguras de decaimento, probabilidades de transição e razões de ramificação. Os resultados obtidos para o 153Eu são comparados com os obtidos recentemente para seus vizinhos ímpares (161,163Dy, 155,157Gd e 159Tb) e com as previsões do Modelo de Bósons e Férmions Interagentes (MBFI). Enquanto os isótopos ímpares de Dy apresentam uma certa concentração de intensidade de dipolo ao redor de 3MeV, os isótopos ímpares de Gd apresentam uma extrema fragmentação de intensidade de dipolo (25 transições para o 155Gd e 90 transições para o 157Gd), na faixa de energia de 2-4 MeV. O núcleo de 153Eu quando comparado aos isótopos ímpares de Dy, Gd e Tb, apresenta uma pequena fragmentação, com baixa intensidade de dipolo. Em geral, a intensidade de dipolo total em núcleos ímpares é menor (por um fator 2-3), quando comparada com seus vizinhos pares. Esta diferença de intensidade entre os isótopos ímpares de Eu, Dy, Gd e Tb é inexplicável até agora. / The aim of this work was to perform Nuclear Resonance Fluorescence (NRF) measurements for the 153Eu deformed nucleus associated to Ml scissors mode. Using the bremsstrahlung photon beam of the Stuttgart Dynamitron (endpoint energy 4.3 MeV) and high resolution Ge spectrometers, detailed information was obtained on excitation energies, decay widths, transition probabilities, and branching ratios. The results are compared to those observed recently for the neighboring odd nuclei 161,163Dy, 155,157Gd and 159Tb and with the Interacting Boson Fermion Model (IBFM). Whereas in the odd Dy isotopes the dipole strength is rather concentrated, both Gd isotopes show a strong fragmentation of the strength into about 25 (155Gd) and 90 transitions (157Gd) in the energy range 2-4 MeV. The nucleus 153Eu as compared to these odd Dy, Gd and Tb isotopes exhibits a small fragmentation with low strength. In general the observed total strength in the odd nuclei is reduced by a factor of 2-3 as compared to their neighboring even-even isotopes. The different fragmentation behavior of the dipole strengths in the odd Dy, Gd, Tb and Eu isotopes is unexplained up to now.

O objetivo do presente trabalho foi determinar, através de medidas de Ressonância Fluorescente Nuclear (RFN) para o núcelo deformado de 153Eu, a intensidade integrada de ressonâncias localizadas de dipolo associadas a modos de movimento como o modo tesoura Ml (ressonâncias anãs). Foi utilizado o feixe de elétrons do acelerador Dynamitron da Universidade de Stuttgart (Eo = 4,3 MeV) e detetores de Ge(HP) e Ge(Li) de alta resolução para a obtenção de informações detalhadas acerca das energias de excitação, larguras de decaimento, probabilidades de transição e razões de ramificação. Os resultados obtidos para o 153Eu são comparados com os obtidos recentemente para seus vizinhos ímpares (161,163Dy, 155,157Gd e 159Tb) e com as previsões do Modelo de Bósons e Férmions Interagentes (MBFI). Enquanto os isótopos ímpares de Dy apresentam uma certa concentração de intensidade de dipolo ao redor de 3MeV, os isótopos ímpares de Gd apresentam uma extrema fragmentação de intensidade de dipolo (25 transições para o 155Gd e 90 transições para o 157Gd), na faixa de energia de 2-4 MeV. O núcleo de 153Eu quando comparado aos isótopos ímpares de Dy, Gd e Tb, apresenta uma pequena fragmentação, com baixa intensidade de dipolo. Em geral, a intensidade de dipolo total em núcleos ímpares é menor (por um fator 2-3), quando comparada com seus vizinhos pares. Esta diferença de intensidade entre os isótopos ímpares de Eu, Dy, Gd e Tb é inexplicável até agora. / The aim of this work was to perform Nuclear Resonance Fluorescence (NRF) measurements for the 153Eu deformed nucleus associated to Ml scissors mode. Using the bremsstrahlung photon beam of the Stuttgart Dynamitron (endpoint energy 4.3 MeV) and high resolution Ge spectrometers, detailed information was obtained on excitation energies, decay widths, transition probabilities, and branching ratios. The results are compared to those observed recently for the neighboring odd nuclei 161,163Dy, 155,157Gd and 159Tb and with the Interacting Boson Fermion Model (IBFM). Whereas in the odd Dy isotopes the dipole strength is rather concentrated, both Gd isotopes show a strong fragmentation of the strength into about 25 (155Gd) and 90 transitions (157Gd) in the energy range 2-4 MeV. The nucleus 153Eu as compared to these odd Dy, Gd and Tb isotopes exhibits a small fragmentation with low strength. In general the observed total strength in the odd nuclei is reduced by a factor of 2-3 as compared to their neighboring even-even isotopes. The different fragmentation behavior of the dipole strengths in the odd Dy, Gd, Tb and Eu isotopes is unexplained up to now.

Subject of the thesis is study of photon strength functions describing the gamma decay of the nucleus. During last 50 years a number of theoretical models for these quantities were proposed, however, their accuracy is still de- batable and its verification has recently been a subject of intensive experimental and theoretical research. In this work measurement of multi-step gamma cas- cades following the radiative neutron capture on target nucleus 167 Er is used to analyse photon strength functions. The experiment was performed with DANCE calorimeter located in Los Alamos Neutron Scattering Center. The experimen- tal spectra are compared with Monte Carlo simulations of electromagnetic decay using the DICEBOX algorithm, based on assumptions of Extreme Statistical Model. Comparison of experimental and simulated spectra is a fundamental tool for studying correctness of theoretical models of photon strength functions. This study provides information mainly about E1 and M1 photon strength functions, especially properties of the so-called scissor mode are analysed.

Title: Photon strength functions in Gd isotopes studied from resonance neutron capture Author: RNDr. Jiří Kroll Department: Intitute of particle and nuclear physics Supervisor: doc. Mgr. Milan Krtička, Ph.D., Intitute of particle and nuclear physics Abstract: Photon strength functions have been studied for more than sixty years. A number of theoretical models was proposed to describe experimental data during that time. However, the correctness of these models is still very questionable and its verification is the subject of very intensive experimental and theoretical activity at present time. In this thesis the analysis of spectra of γ rays following the radiative capture of neutrons on isolated neutron resonances of 152,154−158 Gd nuclei is used to study photon strength functions. Experimental data were measured using segmented DANCE calorimeter that is installed at Los Alamos Neutron Scattering Center in New Mexico, USA. Experimental spectra are then compared with the outputs of Monte Carlo simulation of nuclear elec- tromagnetic decay, performed by DICEBOX code, that is based on the validity of the so-called Extreme Statistical Model. The response of the detector system to generated γ cascades was subsequently calculated using the Geant4 code. An analysis of the data clearly indicates that magnetic...

The γ decay of highly excited nuclear levels can be described within the statistical model of nucleus in terms of the level density and a set of photon strength functions. The knowledge of these quantities enables more accurate calculations of reaction rates in many different reactions which are important especially in nuclear astrophysics and in the development of advanced nuclear reactors. Despite the fact that the photon strength functi- ons have been studied for decades, there are still contradicting experimental results regarding the low energy behavior of dipole strength. One of these ca- ses is the shape of electric dipole photon strength function and the strength of the scissors mode in well-deformed rare-earth nuclei. In this thesis the ana- lyses of γ-ray spectra measured by two different experimental setups are pre- sented. The two-step γ cascades measurements with odd gadolinium targets were performed at the research reactor LVR-15 at the Research Centre Řež. In the multi-step γ cascades experiments the γ rays following resonance ne- utron capture on 161−163 Dy targets were measured with the highly-segmented γ-ray calorimeter Detector for Advanced Neutron Capture Experiments in the Los Alamos Neutron Science Center at Los Alamos National Labora- tory. Experimental spectra were compared...

<p>Bose-Einstein condensates (BECs) in light-induced synthetic gauge fields and spaces can provide a highly-tunable platform for quantum simulations. Chapter 1 presents a short introduction to the concepts of BECs and our BEC machine. Chapter 2 introduces some basic ideas of how to use light-matter interactions to create synthetic gauge fields and spaces for neutral atoms. Three main research topics of the thesis are summarized below.</p> <p>Chapter 3: Recently, using bosonic quasiparticles (including their condensates) as spin carriers in spintronics has become promising for coherent spin transport over macroscopic distances. However, understanding the effects of spin-orbit (SO) coupling and many-body interactions on such a spin transport is barely explored. We study the effects of synthetic SO coupling (which can be turned on and off, not allowed in usual materials) and atomic interactions on the spin transport in an atomic BEC.</p> <p>Chapter 4: Interplay between matter and fields in physical spaces with nontrivial geometries can lead to phenomena unattainable in planar spaces. However, realizing such spaces is often impeded by experimental challenges. We synthesize real and curved synthetic dimensions into a Hall cylinder for a BEC, which develops symmetry-protected topological states absent in the planar counterpart. Our work opens the door to engineering synthetic gauge fields in spaces with a wide range of geometries and observing novel phenomena inherent to such spaces.</p> <p>Chapter 5: Rotational properties of a BEC are important to study its superfluidity. Recent studies have found that SO coupling can change a BEC's rotational and superfluid properties, but this topic is barely explored experimentally. We study rotational dynamics of a SO-coupled BEC in an effective rotating frame induced by a synthetic magnetic field. Our work may allow for studying how SO coupling modify a BEC's rotational and superfluid properties.</p> <p>Chapter 6 presents some possible future directions.</p>