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1
McCarron, Daniel John. "A quantum degenerate mixture of ⁸⁷Rb and ¹³³Cs." Thesis, Durham University, 2011. http://etheses.dur.ac.uk/3242/.
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This thesis reports the formation of a dual-species Bose-Einstein condensate of ⁸⁷Rb and ¹³³Cs in the same trapping potential. Quantum degenerate mixtures exhibit rich physics inaccessible to single species experiments and provide an ideal starting point for the creation of ultracold dipolar molecules. These molecules offer a wealth of new research avenues including precision metrology, quantum simulation and computation. The experimental method exploits the efficient sympathetic cooling of ¹³³Cs via elastic collisions with ⁸⁷Rb, initially in a magnetic quadrupole trap and subsequently in a levitated optical trap. Evaporative cooling in the dipole trap must compete against a high interspecies three-body inelastic collision rate ~ 10⁻²⁵ - 10⁻²⁶ cm⁶/s. The two condensates each contain up to 2 x 10⁴ atoms and exhibit a striking phase separation, revealing the mixture to be immiscible due to strong repulsive interspecies interactions. Sacrificing all the ⁸⁷Rb during the cooling leads to the creation of single-species ¹³³Cs condensates of up to 6 x 10⁴ atoms. In addition this thesis reports the observation of an interspecies Feshbach resonance at 181.7(5)G and the creation of a pure sample of Cs₂ molecules via magneto-association on the 4(g)4 resonance at 19.8 G. These results represent important steps towards the creation of ultracold polar RbCs molecules.
2
Voigt, Arne-Christian. "Heteronuclear Molecules from a Quantum Degenerate Fermi-Fermi Mixture." Diss., lmu, 2009. http://nbn-resolving.de/urn:nbn:de:bvb:19-106171.
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Taglieber, Matthias. "Quantum degeneracy in an atomic fermi-fermi-bose mixture." Diss., kostenfrei, 2008. http://edoc.ub.uni-muenchen.de/8452/.
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Cabrera, Córdova César Raymundo. "Quantum liquid droplets in a mixture of Bose-Einstein condensates." Doctoral thesis, Universitat Politècnica de Catalunya, 2018. http://hdl.handle.net/10803/663331.
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In this thesis, we report on the design and construction of a quantum simulator experiment using quantum gases in Spain. This experiment exploits mixtures of the three isotopes of potassium, which give access in an original approach to the study of Bose-Bose or Bose-Fermi mixtures using the same experimental setup.
We validate our experimental setup with the observation of a Bose-Einstein condensate (BEC) of 41K and 39K. Moreover we observe the dual Bose-Einstein condensation of 39K–41K. These results represents the first observation of BECs in Spain and give access to a novel quantum degenerate mixture in the field. Since the control of interactions in our experiment are crucial, we characterize the scattering properties of the 39K–41K mixture, and spin mixtures of 39K and 41K.
In addition, using a spin mixture of 39K BEC, we report on the observation of a novel state of matter: a composite quantum liquid droplet. This dilute quantum droplet is a liquid-like cluster of ultra-cold atoms self-trapped by attractive mean-field forces and stabilized against collapse by repulsive beyond mean-field many-body effects. This system follows the original proposal where D. Petrov predicted the formation of self-bound liquid droplets in mixtures of Bose-Einstein condensates.
In the first series of experiments, we have observed the formation of quantum droplets in a regime where the Bose-Bose mixture should collapse from the mean-field perspective.We directly measure the droplet size and ultra-low density via high-resolution in situ imaging, and experimentally confirm their self-bound nature.We demonstrate that the existence of these droplets is a striking manifestation of quantum fluctuations. These droplets do not exist in single-component condensates with described with contact interactions. Finally, we observe that for small atom numbers, quantum pressure dissociates the droplets and drives a liquid-to-gas transition, which we map out as a function of interaction strength.
These measurements open an intriguing point of investigation: the difference existing between droplets and bright solitons. In the second series of experiments, we address it by placing the mixture in an optical waveguide, realizing a system that contains both composite bright solitons and quantum liquid droplets. In analogy to non-linear optics, the former can be seen as one-dimensional matter-wave solitons stabilized by dispersion, whereas the latter corresponds to highdimensional solitons stabilized by a higher order non-linearity. We find that depending on atom number, interaction strength and confinement, solitons and droplets can be smoothly connected or remain distinct states coexisting only in a bi-stable region. We measure their spin composition, extract their density for a broad range of parameters, and map out the boundary of the region separating solitons from droplets.
Our experiments demonstrate a novel type of ultra-dilute quantum liquid, stabilized only by contact interactions. They provide an ideal platform for benchmarking complex quantum many-body theories beyond the mean-field approximation in a quantum simulation approach. Furthermore, they constitute a novel playground to explore experimentally self-bound states stabilized by unconventional higher order nonlinearities, relevant in non-linear optics.<br>En este trabajo de tesis se reporta el diseño y la construcción de uno de los experimentos pioneros en España que permite realizar simulaciones cuánticas usando átomos ultra fríos. En este experimento se enfrían hasta alcanzar la degeneración cuántica los tres diferentes isotopos de potasio los cuales permiten, de manera particular y original, el estudio de mezclas cuánticas degeneradas de tipo Bose-Bose o Bose-Fermi.
El funcionamiento del experimento es validado por medio de la producción de condensados de Bose-Einstein de 41K y 39K. Además, se reporta la condensación de la mezcla degenerada 41K - 39K, la cual no había sido previamente reportada en la literatura. Estos resultados
son los primeros de su tipo en España y por lo tanto abren un amplio panorama en el estudio de fenómenos cuánticos en el país. La mezcla cuántica reportada en esta tesis permite acceder a sistemas cuánticos novedosos en el campo de átomos fríos. El control de las interacciones
atómicas es una herramienta ampliamente usada en el campo, por lo cual se han caracterizado las propiedades de dispersión en esta nueva mezcla, así como en diferentes mezclas de espín entre los isotopos 41K y 39K.
El resultado más importante de esta tesis reside en la creación de un nuevo estado de la materia: una gota liquida cuántica ultra-diluida. Esta gota cuántica se compone de una mezcla de dos estados diferentes de espín de 39K. Este líquido se encuentra ligado por sí mismo debido a la compensación de las fuerzas atractivas de campo con el carácter repulsivo de efectos cuánticos que van más allá de la aproximación de campo medio. Este sistema sigue la idea original de D.
Petrov, esta propone la formación de líquidos cuánticos usando mezclas de condensados de Bose-Einstein.
En la primera serie de experimentos, hemos observado la formación de gotas cuánticas en un régimen donde una mezcla de Bose debería de colapsar de acuerdo con teorías de campo medio. Se ha medido su tamaño y ultra-baja densidad por medio de imágenes in situ. De esta manera confirma cómo este líquido permanece ligado por si mismo en la ausencia de confinamiento externo. Hemos demostrado que la existencia de estas gotas cuánticas se debe a una manifestación sorprendente de las fluctuaciones cuánticas. Finalmente hemos observado cómo debido a la presencia de la presión cuántica, debajo de un numero critico de átomos el sistema se disocia en gas dando lugar a una transición cuántica liquido-gas. Esta transición se ha medido experimentalmente como función de las interacciones atómicas entre los átomos.
Estas mediciones traen consigo una pregunta intrigante: ¿Cuál es la diferencia entre nuestras gotas cuánticas y los ya conocidos solitones de materia? En una segunda serie de experimentos, hemos dado respuesta a esta interrogante al estudiar las propiedades de una mezcla de Bose confinada en una guía óptica. En este tipo de geometría ambos estados pueden existir. En analogía a sistemas ópticos no-lineales, solitones son sistemas estabilizados por efectos de dispersión, mientras las gotas cuánticas corresponden a solitones de más alta dimensión
estabilizadas por efectos no lineales de alto orden. Hemos encontrado que, dependiendo del número de átomos, fuerza de interacción y confinamiento, solitones y gotas cuánticas son dos estados cuánticos que pueden estar conectados, permanecer como dos estados distintos, o
coexistir en una región de bi-estabilidad. Se ha medido su composición de espín, densidad del sistema y encontrado experimentalmente la frontera que separa ambos sistemas.
En conclusión, los experimentos mostrados en esta tesis demuestran la existencia de un nuevo liquido cuántico ultra-diluido estabilizado únicamente por interacciones de contacto. Su existencia es puramente debida a las fluctuaciones cuánticas presentes en el sistema. Este sistema
provee una plataforma ideal para el estudio y la comprensión de teorías cuánticas más complejas las cuales van más allá de la aproximación de campo medio.
5
D'Alberto, Jacopo. "Study of a 2D Bose-Fermi mixture with quantum Monte Carlo methods." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/24393/.
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Ultracold gases are an exceptionally versatile platform to test novel physical concepts. Thanks to the development of new experimental techniques, they have greatly advanced our understanding of the physics of many-body systems and allowed precision measurements of fundamental constants. Bose-Fermi mixtures can then be introduced in this context. This novel quantum many-body system is essentially an ultracold gas made up by both bosons and fermions, where tunable attractive or repulsive interactions between the components can be introduced. At T = 0 and for weak interactions the bosons condense while the fermions behave as a Fermi liquid. In particular, a recent system of interest is given by two-dimensional Bose-Fermi mixtures with both Bose-Fermi and Bose-Bose repulsive interactions. In the present work, a Quantum Monte Carlo study is conducted, for a fixed value of boson concentration, at zero-temperature from the weak to the strong Bose-Fermi coupling limit. Variational Monte Carlo and Fixed-Node Diffusion Monte Carlo are applied using an optimized Jastrow-Slater wavefunction, extending previous methodology developed for the three-dimensional case. The results are then compared with perturbative predictions, showing very good agreement in the weak coupling region. Variational Monte Carlo agrees with the analytic predictions only for extremely weak coupling, while Diffusion Monte Carlo proves necessary to recover good agreement over the whole perturbative regime. For stronger couplings, our simulations indicate the tendency of the mixture to form bosonic clusters. This finding would definitively deserve further investigation, which is postponed to future works.
6
Duchon, Eric Nicholas. "Quantum Phase Transitions in the Bose Hubbard Model and in a Bose-Fermi Mixture." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1386002245.
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Konishi, Hideki. "Collisional stability of localized metastable ytterbium atoms immersed in a Fermi sea of lithium." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225386.
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8
Wendland, David. "The equation of state of the Hydrogen-Helium mixture with application to the Sun." Thesis, Lyon, École normale supérieure, 2015. http://www.theses.fr/2015ENSL1029/document.
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L’étude des propriétés d’équilibre d’un système Coulombien quantique à plusieurs composantes présente un intérêt théorique fondamental, au-delà de ses nombreuses applications. Le mélange hydrogène-hélium est omniprésent dans la nébuleuse interstellaire ou les planètes géantes, et c’est aussi le constituant majoritaire du Soleil, où les interactions entre électrons et noyaux sont purement électrostatiques en première approximation.Ce travail est dévolu à l’équation d’état de ce mélange vu comme un plasma quantique constitué de protons, de noyaux d’Hélium et d’électrons. Dans ce cadre, nous développons des méthodes numériques pour estimer des intégrales de chemin représentant des ingrédients essentiels. En outre, nous construisons une nouvelle version de la diagrammatique à la Mayer resommée bien adaptée à nos objectifs.Tout d’abord, nous améliorons le double développement basse température et basse densité, dit SLT, pour l’hydrogène pur, grâce à de meilleures estimations des termes à trois corps, les résultats étant par ailleurs comparés à la fameuse équation d’état OPAL. Les densités plus élevées sont atteintes de manière non-perturbative, en utilisant des fonctions de partition d’entités recombinées suffisamment précises. Ainsi l’ionisation par pression est décrite sur une base théorique robuste. Nous étudions également d’autres quantités d’équilibre, comme l’énergie interne et la vitesse du son. Dans la dernière partie, nous calculons l’équation d’état du mélange hydrogène-hélium en incluant les effets d’écran associés aux ions He+, ainsi que des corrections à la Debye déterminées de manière auto-cohérente. Nos résultats nous permettent de comprendre le contenu physique d’approches ad-hoc et de déterminer leurs régimes de validité. Nous obtenons aussi une description plus fiable du mélange, qui devrait être précise le long de l'adiabate du Soleil<br>The study of the thermodynamic properties of a multi-component quantum Coulomb system is of fundamental theoretical interest and has, beyond that, a wide range of applications. The Hydrogen-Helium mixture can be found in the interstellar nebulae and giant planets, however the most prominent example is the Sun. Here the interaction between the electrons and the nuclei is almost purely electrostatic.In this work we study the equation of state of the Hydrogen-Helium mixture starting from first principles, meaning the fundamental Coulomb interaction of its constituting particles. In this context we develop numerical methods to study the few-particle clusters appearing in the theory by using the path integral language. To capture the effects of the long-range Coulomb interaction between the fundamental particles, we construct a new version of Mayer-diagrammatic, which is appropriate for our purposes. In a first step, we ameliorate the scaled-low-temperature (SLT) equation of state, valid in the limit of low density and low temperature, by taking three-body terms into account and we compare the predictions to the well-established OPAL equation of state. Higher densities are accessed by direct inversion of the density equations and by the use of cluster functions that include screening effects. These cluster functions put the influence of screening on the ionization, unto now treated ad-hoc, on a theoretically well-grounded basis. We also inspect other equilibrium quantities such as the speed of sound and the inner energy. In the last part we calculate the equation of state of the Hydrogen-Helium mixture including the charged He+ ions in the screening process. Our work gives insights in the physical content of previous phenomenological descriptions and helps to better determine their range of validity. The equation of state derived in this thesis is expected to be very precise as well as reliable for conditions found in the Sun
9
Laurent, Sébastien. "Dynamics and stability of a Bose-Fermi mixture : counterflow of superfluids and inelastic decay in a strongly interacting gas." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEE023/document.
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La compréhension des effets des interactions dans un ensemble de particules quantiques représente un enjeu majeur de la physique moderne. Les atomes ultra-froids sont rapidement devenus un outil incomparable pour étudier ces systèmes quantiques fortement corrélés. Dans cette thèse, nous présentons plusieurs travaux portant sur les propriétés d’un mélange de superfluides de Bose et de Fermi créé à l’aide de vapeurs ultra-froides de ⁷Li et de ⁶Li. Nous étudions tout d'abord les propriétés hydrodynamiques du mélange en créant un contre-courant entre les superfluides. L'écoulement est dissipatif uniquement au dessus d'une vitesse critique que nous mesurons dans le crossover BEC-BCS. Une simulation numérique d’un contre-courant de deux condensats permet de mieux comprendre les mécanismes sous-jacents mis en jeu dans la dynamique. En particulier, l'étude numérique fournit des preuves supplémentaires que l'origine de la dissipation dans nos expériences est liée à l'émission d'excitation élémentaires dans chaque superfluide. Finalement, nous nous intéressons aux pertes inélastiques par recombinaison à trois corps qui peuvent limiter la stabilité de nos nuages. Ces pertes sont intimement liées aux corrélations à courte distance présentes dans le système et sont ainsi connectées aux propriétés universelles du gaz quantique. Cela se manifeste notamment par l’apparition de dépendances en densité ou en température inusuelles du taux de perte lorsque le système devient fortement corrélé. Nous démontrons cet effet dans deux exemples où les interactions sont résonantes, le cas du gaz de Bose unitaire et celui de notre mélange de superfluides Bose-Fermi. Plus généralement, nos travaux montrent que ces pertes inélastiques peuvent être utilisées pour sonder les corrélations quantiques dans un système en fortes interactions<br>Understanding the effect of interactions in quantum many-body systems presents some of the most compelling challenges in modern physics. Ultracold atoms have emerged as a versatile platform to engineer and investigate these strongly correlated systems. In this thesis, we study the properties of a mixture of Bose and Fermi superfluids with tunable interactions produced using ultracold vapors of ⁷Li and ⁶Li. We first study the hydrodynamic properties of the mixture by creating a counterflow between the superfluids. The relative motion only exhibit dissipation above a critical velocity that we measure in the BEC-BCS crossover. A numerical simulation of counterflowing condensates allows for a better understanding of the underlying mechanisms at play in the dynamics. In particular, this numerical study provides additional evidence that the onset of friction in our experiment is due to the simultaneous generation of elementary excitations in both superfluids. Finally, we consider the inelastic losses that occur via three-body recombination in our cold gases. This few-body process is intimately related to short-distance correlations and is thereby connected to the universal properties of the many-body system. This manifests as the apparition of an unusual dependence on density or temperature in the loss rate when increasing the interactions. We demonstrate this effect in two examples where interactions are resonant: the case of a dilute unitary Bose gas and the one of impurities weakly coupled to a unitary Fermi gas. More generally, our work shows that inelastic losses can be used to probe quantum correlations in a many-body system
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PANTALEI, CLAUDIA. "Single-particle dynamics of helium mixtures and 4He in nanometric confinement." Doctoral thesis, Università degli Studi di Roma "Tor Vergata", 2008. http://hdl.handle.net/2108/473.
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Scopo di questa tesi e' lo studio, tramite Deep Inelastic Neutron Scattering, della
dinamica microscopica di due differenti sistemi di elio, a bassa temperatura (circa 2
K): una miscela isotopica (nella fase fluida e vicino al punto di melting) e 4He in in
confinamento nanometrico.
L'interesse per l'elio, gia' dai primi decenni del `900, nasce dalla sua unica proprieta':
e' l'unico elemento in natura a non avere una fase solida allo zero assoluto. A basse
temperature, quindi, presenta effetti quantistici, normalmente trascurabili in altri
sistemi fisici, che nelle stesse condizioni solidificano. l'elio e' quindi l'unico banco di
prova per i modelli teorici quantistici, in particolare per lo studio di bosoni e fermioni
interagenti.
In questo contesto, molti esperimenti sono stati effettuati sull'elio, sia nella fase liquida che solida. Misure su 3He e 4He hanno mostrato che l'energia cinetica dei liquidi
puri dipende dalla densita' del sistema, crescendo con una diminuzione del volume
molare. D'altra parte, la dinamica microscopica delle miscele mostra un differente
comportamento rispetto al 3He e 4He puri: l'energia cinetica media dell'isotopo piu'
leggero, a volumi molari maggiori di 25cm3/mole, sembra essere indipendente dal
volume molare e dalla concentrazione. Questo andamento potrebbe essere spiegato
da effetti quantistici, come gli effetti di scambio. Nella prima parte del presente
lavoro si e' investigata la dinamica delle miscele per volumi molari tra 22cm3/mole
e 25cm3/mole, e gli esperimenti compiuti hanno mostrato che in questo range di
volumi molari l'energia cinetica media degli atomi di 3He risulta dipendente dal volume molare, aumentando fino ad avere un valore corrispondente a quello del 3He
puro.
Recentemente sono state compiute anche misure per studiare l'influenza di un confinamento sull'elio. Esperimenti su 4He, adsorbito in superfici piane o substrati
porosi, hanno rivelato un elevato aumento nel valore dell'energia cinetica. Questo
comportamento e' stato attribuito alla localizzazione degli atomi di He dovuta al
potenziale di interazione He-substrato, che influenza fortemente i primi due o tre layers. Questi tipi di effetti possono essere studiati confinando 4He in pori cilindrici con
differenti diametri dei pori. Scopo della seconda parte di questa tesi e' stata appunto
quella di determinare l'energia cinetica media degli atomi di 4He adsorbiti in sistemi
nanoporosi a geometria cilindrica (Xerogel) con due diametri medi dei pori, di 24ºA
160ºA, per valutare la dipendenza della dinamica a singola particella con la dimensione dei pori e con il tipo di geometria. Le misure sono state effettuate a T=2.5K, a
pressione di vapor saturo e con un riempimento dei pori del 95%. L'esperimento ha
mostrato che l'energia cinetica del 4He nei pori e' maggiore rispetto a quella del 4He
liquido nelle stesse condizioni. I risultati sono stati interpretati tramite un modello
teorico, secondo il quale gli atomi si posizionano in anelli concentrici, stratificando
layer per layer, e con un'energia cinetica dipendente dal rapporto tra il diametro del
poro e quello dell'atomo di elio.<br>The aim of this thesis work is the study, by means of Deep Inelastic Neutron Scatter-
ing, of the microscopic dynamics of two different helium systems at low temperature
(T=2K): an isotopic helium mixture (in the fluid phase and near the melting point)
and a system of 4He in nanometric confinement.
The interest in the helium, from the first decades of 1900, is due to its unique features: it is the only element in nature that doesn't have a solid phase at absolute
zero. Thus, at low temperatures it presents quantum effects, usually negligible in
other physical systems that in this condition crystallise. The helium is thus the
unique test-bed for theoretical quantum models, in particular for studying the interacting boson (4He) and fermion (3He) systems. Moreover, if in 4He are added some
atoms of 3He it is possible to derive important information about the interplay of
these two statistics.
In this context, several experiments on liquid and solid helium have been performed.
Measurements on pure 3He and 4He have shown that the mean kinetic energy of
pure liquids depends on the density of the system and increases decreasing the molar volume. On the other hand, the microscopic dynamics of helium mixtures reveals
quite a different picture with respect to pure 3He and 4He: the mean kinetic energy
of the light isotope, above a molar volume of 25cm3/mole, shows a remarkable independence from molar volume and concentration. This behaviour could be explained
by quantum effects, such as exchange effects. The first part of the present work deals
with the experiments performed to investigate the dynamics of the mixtures from
22cm3/mole to 25cm3/mole and shows how, at these low molar volumes, the mean
kinetic energy of 3He starts again to be strongly dependent on the molar volume,
increasing until reaching, at 22.7cm3/mole, the corresponding value of pure helium.
Recent measurements have been also performed to investigate the influence of confinement on helium. Experiments on 4He, adsorbed in flat surface or slit geometry
porous substrates, have shown a large increase in helium mean kinetic energy. This
has been attributed to the strong localisation effects induced by the helium-substrate
interaction potential, which mainly influence the firsts two or three adsorbed layers.
Such effects can be also investigated by confining 4He atoms in cylindrical pore geometries and by studying their dynamics as function of pore size. Aim of the second
part of the thesis has been the determination of the single particle mean kinetic
energy of 4He adsorbed in cylindrical silica nanopores (Xerogel) having two different
pore diameters, namely, 24 ºAand 160 ºA, and to evaluate the dependence of single-
particle dynamics on pore sizes, layer coverage, and confining system geometry. The
measurements have been performed at a temperature of T=2.5K, saturated vapour
pressure, and 95% volume filling. Significant changes in the values of the single particle mean kinetic energy are found: they are remarkably higher than the value of
normal liquid 4He at the same conditions. The results are interpreted in terms of
a model in which 4He atoms are arranged in concentric annuli along the cylindrical
pore axis, growing layer-by-layer and with the mean kinetic energy mainly dependent
on the ratio between the atomic diameter and the pore diameter.
11
Guenther, Nils Eric. "Dynamics of quantum mixtures." Doctoral thesis, Universitat Politècnica de Catalunya, 2021. http://hdl.handle.net/10803/672677.
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At sufficiently low temperatures, fluids of bosonic particles may undergo a phase transition, below which a Bose-Einstein condensate (BEC) forms. The BEC is one of the most fundamental concepts in many-body quantum physics and provides a paradigmatic example of a collective matter wave. The distinctive mixture of fluid-like and particle-like behavior this state exhibits leads to the emergence of unique features such as vortex quantization, but also to an often exotic interaction with other matter as well as its environment. The goal of my thesis is a further theoretical investigation of the latter, along two specific lines of research. Correspondingly, this manuscript is divided into two main parts.
In the first part, I studied the fundamental polaron problem in the case of a bosonic bath: A BEC interacting with a single distinguishable impurity, a quantum particle on the same scale as the constituent particles of the condensate, which can often be described as a 'dressed' quasiparticle, called the polaron. The focus of this thesis is dilute BECs of ultra-cold atomic vapors, where historically the BEC state was first observed experimentally and the underlying atomic interactions can be controlled to hitherto unprecedented degree via Feshbach resonances. Of particular interest is the case of strong interactions between the impurity and the bosons, the unitary-limited regime. Such impurity systems have been first probed experimentally in recent years, however due to the theoretical complexity and physical richness of the condensate state as well as experimental limitations, the nature of the compound system is not completely understood at strong interactions. I present two theoretical models in this part of the thesis which predict qualitatively new phenomena. In the first, I extended a scheme used in previous work unrelated to me, including the effect of finite temperature below the transition point to take into account the two-fluid nature of the bosons. This scheme predicts a splitting of a single quasi-particle branch at zero temperature into two branches upon heating, and a general strong temperature dependence of the quasi-particle properties. In the second work, I developed a new variational ansatz tailored for describing large dressing of the impurity. This ansatz predicts that for sufficiently weak intra-bosonic repulsion the impurity can bind a macroscopic but coherent and dilute cloud of bosons of sizes comparable to the healing length of the condensate.
In the second part of my thesis, I present work focusing on the interplay of a condensate and the geometry of its containment. Well known features of condensates are superfluidity and the quantization of vorticity. Considering a superfluid embedded on a two-dimensional surface, I studied the dynamics of point vortices on curved surfaces in the framework of potential flow theory, with a focus on non-simply connected geometry. In a work presented in this thesis revolving around cylinder- and related geometries I derived the generating potential of a single point vortex, which predicts that the dynamics are modified by the quantization of flow around the circumference of the cylinder. In particular, a single vortex is always forced to move along the longitudinal axis of the cylinder, providing a powerful marker for superfluidity. In a following work regarding a torus-shaped embedding as well as related more general surfaces, I derived the generating potential for a single and multiple vortex-anti vortex pairs and predicted a significant change of local dynamics due to the macroscopic quantization of flow and to the non-trivial curvature of the embedding surface.<br>A temperaturas suficientemente bajas, un fluido compuesto por partículas bosónicas puede experimentar una transición de fase, dando lugar a un condensado de Bose-Einstein (CBE). El CBE es uno de los conceptos fundamentales en física cuántica de muchos cuerpos, suponiendo un ejemplo paradigmático de onda colectiva de materia. La pecular mezcla de comportamientos tipo fluido y tipo partícula que exhibe este estado da lugar a rasgos únicos como la cuantización de vórtices, pero también a una interacción exótica con otros tipos de materia, así como con su entorno. El objetivo de mi tesis es una investigación teórica más extensa de estas propiedades, a través de dos líneas diferentes. En la primera parte he estudiado el problema fundamental del polarón para el caso de un baño bosónico: un CBE interactuando con una única impureza distinguible, una partícula cuántica de la misma escala que las partículas que constituyen el condensado, la cual se puede describir a menudo como una cuasipartícula 'vestida' llamada polarón. El objetivo de esta tesis tiene lugar en el contexto de un CBE diluido formado vapores de átomos ultrafríos, donde, desde un punto de vista histórico, el CBE fue observado experimentalmente por primera vez, y donde las interacciones atómicas subyacentes pueden ser controladas hasta un grado sin precedentes a través de resonancias de Feshbach. Un caso particularmente interesante es el de interacciones fuertes entre la impureza y los bosones, el régimen del límite unitario. Tales sistemas de impurezas se han observado experimentalmente en los últimos años. Sin embargo, debido a la complejidad teórica y a la riqueza del estado condensado unido a las limitaciones experimentales, la naturaleza del sistema compuesto no se entiende por completo para interacciones fuertes. En esta tesis presento dos modelos teóricos que predicen de forma cualitativa nuevos fenómenos. En el primero, extiendo un esquema usado en trabajos previos al mío, incluyendo el efecto de una temperatura finita por debajo del punto de transición para tener en cuenta la naturaleza bifluida de los bosones a tales temperaturas intermedias. Este esquema predice una separación en dos de una única rama de cuasipartículas al aumentar de la temperatura, así como una dependencia general fuerte de la temperatura sobre las propiedades de las cuasipartículas. En el segundo trabajo, desarrollo un modelo variacional diseñado para describir grandes revestimientos de la impureza. Esta estimación predice como para repulsiones intrabosónicas suficientemente débiles la impureza puede ligar una nube macroscópica pero coherente y diluida de bosones de tamaños comparables a la longitud de coherencia del condensado. En la segunda parte de mi tesis, presento trabajos que se enfocan en la interacción entre un condensado y la geometría del recipiente que lo contiene. Algunos de los rasgos conocidos de un condensado son su superfluidez y la cuantización de la vorticidad. Considerando un superfluido contenido en una superficie bidimensional, estudio la dinámica de vórtices puntuales en superficies curvas en el contexto de la teoría de flujo de potencial, con un enfoque en geometrías no simplemente conexas. En un trabajo presentado en esta parte de la tesis acerca de geometrías cilíndricas, derivo el potencial generador de un único vórtice puntual, prediciendo como la dinámica se ve modificada por la cuantización del flujo a lo largo de la circumferencia del cilindro. En particular, este está forzado a moverse siempre a través de su eje longitudinal, aportando un poderoso marcador de superfluidez. En otro trabajo acerca de superficies con forma de toro, así como de superficies relacionadas más generales, derivo el potencial generador tanto de un único como de múltiples pares vórtices - antivórtices y predigo un cambio significativo de dinámicas locales debido a la cuantización macroscópica del flujo y a la curvatura no trivial de la superficie de incrustación.<br>Fotònica
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TRAMONTO, FILIPPO. "MICROSCOPIC STUDIES OF STATIC AND DYNAMIC PROPERTIES IN QUANTUM LIQUIDS AND GASES." Doctoral thesis, Università degli Studi di Milano, 2015. http://hdl.handle.net/2434/260418.
Full textAbstract:
In this thesis I present studies of a number of quantum many-body Bose systems via Quantum Monte Carlo methods.
We investigated the dynamic structure factor of a hard-sphere Bose system simulated at T=0 at different densities, from the dilute to the strongly interacting regimes. By increasing the density we observed the spectrum evolves from the weakly interacting Bogoliubov to a phonon-maxon-roton dispersion, but also the emergence of a broad multi-quasiparticle component. For a system with sphere radius and density corresponding to superfluid 4He at equilibrium, we found good agreement with the spectrum in the roton region.
In another work, a liquid of distinguishable 4He atoms near freezing at T=1 K was studied to compute the equation of state and static density response function. The results of this study have been used to improve the description of the superfluid-to-solid transition within the Density Functional Theory.
Measurements of crystallization kinetics in supercooled liquid p-H2--o-D2 mixtures showed a slowdown with respect to the pure counterparts. In order to contribute to the interpretation of these results we simulated these metastable mixtures. We found differences in the quantum delocalization of the two isotopic molecules, which result in different effective sizes. We characterized also the differences in the local order around the molecules of each species. These results revealed that the observed slowdown is due to purely quantum effects.
Finally, in a QMC study of ion Ar+ doped 4He nanodroplets at T=1 K, we computed density profiles, energies, and investigated local order around the Ar+ ion. We found stable solid structures around the ion composed of three solvation shells having the shape of platonic solids: an icosahedron, a dodecahedron, and, again, an icosahedron, with 12, 20, and 12 4He atoms, going from the inner to the outer shell respectively. These results confirmed the interpretation of experimental measurements of the abundances of Ar+@4He nanodroplets.
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Wu, Cheng-Hsun Ph D. Massachusetts Institute of Technology. "Strongly interacting quantum mixtures of ultracold atoms." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/83817.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2013.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 198-202).<br>This thesis describes the construction of a new apparatus for ultracold quantum gases as well as the scientific results this machine has produced so far. This new apparatus is capable of simultaneously cooling and trapping lithium, sodium, and potassium. It therefore provides a platform to study a large variety of quantum mixtures. Three main experimental results are presented. Firstly, the direct cooling of "K to Bose-Einstein condensation is presented. Then the 41K atoms provide the coolant for 6Li and 40K, achieving a triply degenerate gas of 6Li -40K -41K. In particular, a broad interspecies Feshbach resonance between 40K -41K is observed, opening a new pathway to study a strongly interacting isotopic Bose-Fermi mixture of 40K -41K. Secondly, a new Bose-Fermi mixture of 23Na -40K is introduced. We show that 23Na is a very efficient coolant for 40K by sympathetically cooling 40K to quantum degeneracy with the help of a 23Na condensate. Moreover, over thirty interspecies Feshbach resonances are identified, paving the way to study strongly interacting Bose- Fermi problems, in particular the Bose polaron problem. Thirdly, we report on the first formation of ultracold fermionic Feshbach molecules of 23Na40K by radio-frequency association. The lifetime of the nearly degenerate molecular gas exceeds 100 ms in the vicinity of the Feshbach resonance. The NaK molecule features chemical stability in its ground state in contrast to the case of the KRb molecule. Therefore, our work opens up the prospect of creating chemically stable, fermionic ground state molecules of 23Na40K where strong, long-range dipolar interactions will set the dominant energy scale. Finally, the thesis concludes with an outlook on future topics in polaron physics and quantum dipolar gases, which can be studied using the new apparatus.<br>by Cheng-Hsun Wu.<br>Ph.D.
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Cikojević, Viktor. "Ab-initio quantum Monte Carlo study of ultracold atomic mixtures." Doctoral thesis, Universitat Politècnica de Catalunya, 2021. http://hdl.handle.net/10803/672119.
Full textAbstract:
The properties of mixtures of Bose-Einstein condensates at T=0 have been investigated using quantum Monte Carlo (QMC) methods and Density Functional Theory (DFT) with the aim of understanding physics beyond the mean-field theory in Bose-Bose mixtures. In particular, quantum liquid droplets with attractive intraspecies and repulsive interspecies attraction were studied, for which we observed significant contributions beyond Lee Huang Yang (LHY) theory that affect the energy, saturation density, and surface tension. The critical atom number in droplets in free space for total number of atoms N between N=30 and N=2000 was obtained. Results of the surface tension for three values of the attractive interspecies interactions are presented. For a homogeneous system, extensive calculations of the equations of state were performed and we report the influence of finite-range effects in beyond-Bogoliubov theory. In systems interacting with a small (large) effective range, we observe repulsive (attractive) beyond-LHY contributions to the energy. For the droplets in a mixture of 39K atoms, which were observed experimentally for the first time, the calculations of equations of state were performed. Combining QMC-built functionals with DFT, the discrepancy in the estimation of critical atom number between the mean-field theory and experimental results was explained by the proper inclusion of the effective range in inter-particle interaction models. The influence of finite-range effects on breathing and quadrupole modes in 39K quantum droplets was investigated. We predicted a significant deviation in the excitation frequencies when entering a more correlated regime. Finally, the phase diagram of repulsive Bose-Bose mixtures in a spherical harmonic trap using Quantum Monte Carlo calculations was studied. Density profiles were obtained reported and we found the occurrence of three phases: separation of condensates in two blobs, fully mixed and shell-separated phase. A comparison with the Gross-Pitaevskii solutions showed a large deviation in the regime of large mass imbalance and strong interactions. We showed the universality in the density profiles with respect to the s-wave scattering length and found numerical evidence for Gross-Pitaevskii scaling present beyond the regime of applicability of Gross-Pitaevskii equations.<br>Hemos investigado las propiedades de las mezclas de condensados de Bose-Einstein en el límite de temperatura cero. Para ello hemos usado métodos cuánticos de Monte Carlo (QMC) y la teoría del funcional de la densidad (DFT) con el objetivo de comprender la física más allá de la teoría del campo medio en las mezclas bosónicas. En particular, se estudiaron las gotas de líquido cuántico originadas con interacciones atractivas entre especies distinats y repulsivas entre especies iguales. Observamos contribuciones significativas más allá de la teoría de Lee Huang Yang (LHY) que afectan a la energía, la densidad de saturación y la tensión superficial. Calculamos el número crítico de átomos en gotitas en el espacio libre para un número total de átomos N entre N = 30 y N = 2000. Obtuvimos resultados de la tensión superficial para tres valores de las interacciones atractivas entre especies. Para un sistema homogéneo, se realizaron cálculos extensos de las ecuaciones de estado y reportamos la influencia de los efectos de rango finito en la teoría, más allá de Bogoliubov. En sistemas que interactúan con un rango efectivo pequeño (grande), observamos contribuciones repulsivas (atractivas) a la energia más allá de LHY. Para las gotitas en una mezcla de 39K átomos, que se observaron experimentalmente por primera vez en ICFO, se realizaron los cálculos de ecuaciones de estado. Combinando funciones obtenidas de QMC con DFT, explicamos la discrepancia en la estimación del número crítico de átomos, entre la teoría de campo medio y los resultados experimentales, mediante la inclusión adecuada del rango efectivo en los modelos de interacción entre partículas. Se investigó la influencia de los efectos de rango finito en los modos monopolar y cuadrupolar en gotas cuánticas de 39K. Predijimos una desviación significativa en las frecuencias de excitación al entrar en un régimen más correlacionado. Finalmente, se estudió el diagrama de fase de mezclas bosóncas repulsivas en una trampa armónica esférica utilizando cálculos de Quantum Monte Carlo. Se obtuvieron los perfiles de densidad y se probó la existencia de tres fases: separación de condensados en dos lóbulos, una fase completamente mezclada y una fase separada con capas esféricas. Una comparación con las soluciones de Gross-Pitaevskii mostró una gran desviación en el régimen de gran desequilibrio de masas e interacciones fuertes. Finalmente, mostramos la presencia de universalidad en los perfiles de densidad, con respecto a la longitud de dispersión en onda S, y encontramos evidencia numérica del factor de escala de Gross-Pitaevskii más allá del régimen de aplicabilidad de las propias ecuaciones de Gross-Pitaevskii.<br>Ultrahladne atomske mješavine istražene ab-initio kvantnom Monte Carlo metodom.
Svojstva smjesa Bose-Einsteinovih kondenzata pri T = 0 istražena su korištenjem metoda kvantnog
Monte Carla (QMC) i teorije funkcionala gustoće (DFT) s ciljem proučavanja fizike izvan teorije srednjeg
polja u bozonskim mješavinama. Proučili smo kvantne kapljice s jednakim i odbojnim interakcijama
između atoma istovrsne komponente te privlačnim interakcijama atoma različitih komponenti u interakciji
i opazili smo značajne doprinose povrh Lee Huang Yang (LHY) teorije koji utječu na energiju, saturacijsku
gustoću i površinsku napetost. Odredili smo kritični broj atoma za kapljice u slobodnom prostoru
za broj atoma u kapljici N između N = 30 i N = 2000. Izračunali smo površinsku napetost za
tri vrijednosti privlačnih međuatomskih interakcija. Izvršili smo opsežne proračune jednadžbi stanja
iznimno rijetke tekućine bozonske mješavine i uočili utjecaj efekata konačnog dosega koji nije predviđen
Bogoliubovljevom teorijom. U sustavima koji interagiraju s malim (velikim) efektivnim dosegom,
opaženi su odbojni (privlačni) doprinosi koje ne predviđa LHY teorija. Izračunali smo jednadžbe
stanja za kapljice bozonskih mješavina koje su po prvi put eksperimentalno uočene u smjesi 39K atoma.
Kombinirajući funkcionale gustoće izgrađene pomoću kvantnog Monte Carla s DFT-om, neslaganje u
procjeni kritičnog broja atoma između teorije srednjeg polja i eksperimentalnih rezultata je objašnjeno
preko pravilnog uključivanja efektivnog dosega u modele međudjelovanja čestica. Istražen je utjecaj
efektivnog dosega na pobuđenja kapljice 39K, i to na mod disanja i kvadrupolni mod. Dobiveni rezultati
prikazuju značajno odstupanje frekvencija pobude pri ulasku u korelirani režim. Detaljno smo proučili
fazni dijagram odbojnih Bose-Bose mješavina u sfernoj harmonijskoj zamci koristeći kvantne Monte
Carlo račune. Dobiveni su profili gustoće koji pokazuju pojavu tri faze: separacija kondenzata u dvije
nakupine, potpuno miješanje i separacije u obliku ljuske. Usporedba s riješenjima Gross-Pitaevskii
jednadžbi pokazuje veliko odstupanje u režimu velike masene neravnoteže i jakih interakcija. Pokazali
smo univerzalnost profila gustoće s obzirom na s-valnu duljinu raspršenja te postojanje Gross-Pitaevskii
skaliranja prisutnog izvan dosega primjenjivosti Gross-Pitaevskii jednadžbi.
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Ridinger, Armin. "Towards quantum degenerate Fermi mixtures : photoassociation of weakly bound 6Li40K molecules." Phd thesis, Ecole Normale Supérieure de Paris - ENS Paris, 2011. http://tel.archives-ouvertes.fr/tel-00613211.
Full textAbstract:
Mon projet de thèse a eu pour objectif la construction d'un dispositif expérimental visant à étudier, à très basse température, un mélange de gaz dégénéré composé de deux espèces fermioniques: 6Li et 40K. Une description détaillée du montage de sa mise en place ainsi qu'une caractérisation du dispositif sont présentées. Nous avons réalisé un piège magnéto-optique à deux espèces avec un très grand nombre d'atomes, et un transport magnétique sur une grande distance. Les premières expériences avec le mélange atomique ont permis la première création de molécules hétéronucléaires excitées 6Li40K* par photoassociation. Nous avons enregistré et assigné des spectres de photoassociation pour les états les plus faiblement liés de sept potentiels moléculaires et nous en avons déduit la forme des potentiels à longues distances. Nos résultats ouvrent la voie vers la formation de molécules bosoniques 6Li40K ultra-froides dans leur état fondamental, caractérisé par un grand moment dipolaire électrique permanent. Sur le plan théorique, nous avons développé une nouvelle méthode pour la manipulation des particules quantiques, qui pourrait être appliquée aux molécules 6Li40K. Cette méthode consiste à piéger les particules dans un potentiel oscillant rapidement et induire un changement instantané de phase du potentiel (un saut de phase). Nous montrons que le mouvement moyen des particules peut ainsi être manipulé de manière contrôlée. La méthode proposée a trouvé une première application pour les condensats de Bose-Einstein piégés à l'aide d'un piège magnétique du type "TOP".
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Albus, Alexander. "Mixtures of Bosonic and Fermionic atoms." Phd thesis, Universität Potsdam, 2003. http://opus.kobv.de/ubp/volltexte/2005/98/.
Full textAbstract:
Ziel der Arbeit war die systematische theoretische Behandlung von Gemischen aus bosonischen und fermionischen Atomen in einem Parameterbereich, der sich zur Beschreibung von aktuellen Experimenten mit ultra-kalten atomaren Gasen eignet.<br />
<br />
Zuerst wurde der Formalismus der Quantenfeldtheorie auf homogene, atomare Boson-Fermion Gemische erweitert, um grundlegende Größen wie Quasiteilchenspektren, die Grundzustandsenergie und daraus abgeleitete Größen über die Molekularfeldtheorie hinaus zu berechnen.<br />
<br />
Unter Zuhilfenahme der dieser Resultate System wurde ein Boson-Fermion Gemisch in einem Fallenpotential im Rahmen der Dichtefunktionaltheorie beschrieben. Daraus konnten die Dichteprofile ermittelt werden und es ließen sich drei Bereiche im Phasendiagramm identifizieren: <br />
(i) ein Bereich eines stabilen Gemisches,<br />
(ii) ein Bereich, in dem die Spezies entmischt sind und <br />
(iii) ein Bereich, in dem das System kollabiert.<br />
<br />
Im letzten dieser drei Fällen waren Austausch--Korrelationseffekte signifikant. Weiterhin wurde die Änderung der kritischen Temperatur der Bose-Einstein-Kondensation aufgrund der Boson-Fermion-Wechselwirkung berechnet. Verursacht wird dieser Effekt von Dichtumverteilungen aufgrund der Wechselwirkung.<br />
<br />
Dann wurden Boson-Fermion Gemische in optischen Gittern betrachtet. Ein Stabilitätskriterium gegen Phasenentmischung wurde gefunden und es ließen sich Bedingungen für einen supraflüssig zu Mott-isolations Phasenübergang angeben. Diese wurden sowohl mittels einer Molekularfeldrechnung als auch numerisch im Rahmen eines Gutzwilleransatzes gefunden. Es wurden weiterhin neuartige frustrierte Grundzustände im Fall von sehr großen Gitterstärken gefunden.<br>The theory of atomic Boson-Fermion mixtures in the dilute limit beyond mean-field is considered in this thesis.<br />
Extending the formalism of quantum field theory we derived expressions for the quasi-particle excitation spectra, the ground state energy, and related quantities for a homogenous system to first order in the dilute gas parameter.<br />
<br />
In the framework of density functional theory we could carry over the previous results to inhomogeneous systems. We then determined to density distributions for various parameter values and identified three different phase regions: <br />
(i) a stable mixed regime, <br />
(ii) a phase separated regime, and <br />
(iii) a collapsed regime. <br />
<br />
We found a significant contribution of exchange-correlation effects in the latter case. Next, we determined the shift of the Bose-Einstein condensation temperature caused by Boson-Fermion interactions in a harmonic trap due to redistribution of the density profiles.<br />
<br />
We then considered Boson-Fermion mixtures in optical lattices. We calculated the criterion for stability against phase separation, identified the Mott-insulating and superfluid regimes both, analytically within a mean-field calculation, and numerically by virtue of a Gutzwiller Ansatz. We also found new frustrated ground states in the limit of very strong lattices.
<br><br>----<br>Anmerkung:<br>
Der Autor ist Träger des durch die Physikalische Gesellschaft zu Berlin vergebenen Carl-Ramsauer-Preises 2004 für die jeweils beste Dissertation der vier Universitäten Freie Universität Berlin, Humboldt-Universität zu Berlin, Technische Universität Berlin und Universität Potsdam.
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Kimene, Kaya Boniface Dimitri Christel. "Crossovers and phase transitions in Bose-Fermi mixtures." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86471.
Full textAbstract:
Thesis (MSc)--Stellenbosch University, 2014.<br>ENGLISH ABSTRACT: We present a theoretical approach that allows for the description of trapped Bose-Fermi mixtures
with a tunable interspecies interaction in the vicinity of a Feshbach resonance magnetic field.The
many-body physics of the system is treated at equilibrium using the well-established mean-field
and local density approximations. This reduces the physics locally to that of a homogeneous
system. We observe a rich local phase structure exhibiting both first and second order phase
transitions between the normal and BEC phases. We also consider the global properties of the
mixture at a fixed number of particles and investigate how the density profiles and the populations
of the various particle species depend on the detuning and trap profile.<br>AFRIKAANSE OPSOMMING: Ons beskou ’n teoretiese beskrywing van gevangde Bose-Fermi mengsels met ’n verstelbare interspesie
wisselwerking in die teenwoordigheid van ’n magneties-geïnduseerde Feshbach resonansie.
Die veeldeeltjiefisika van die sisteem word by ekwilibrium binne die welbekende gemiddelde-veld
en lokale-digtheid benaderings hanteer. Sodoende word die fisika lokaal tot die van ’n homogene
sisteem gereduseer. Ons neem ’n ryk fase-struktuur waar met beide eerste- en tweede-orde
fase-oorgange tussen die normale en BEK fases. Ons beskou ook die globale eienskappe van die
mengsel by ’n vaste totale aantal deeltjies en ondersoek hoe die digtheidsprofiele en deeltjiegetalle
van die afstemming en die profiel van die val afhang.
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Hara, Hideaki. "Production of Quantum Degenerate Mixtures of Alkali and Alkaline-Earth-Like Atoms." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/185217.
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Santiago, González Ibon. "LiNaK : multi-species apparatus for the study of ultracold quantum degenerate mixtures." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/77478.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Physics, 2012.<br>Cataloged from student-submitted PDF version of thesis.<br>Includes bibliographical references (p. 109-113).<br>This thesis describes the construction of a versatile apparatus to study ultracold quantum mixtures capable of simultaneously cooling fermionic ⁶Li and ⁴⁰K, as well as the bosonic ⁴¹K. The main features of the experimental setup are presented, in particular the addition of a new species ²³Na, which has enabled the study of the Bose-Fermi mixture ²³Na-⁴⁰K. Three main experimental benchmarks are outlined: first, the production of a Bose-Einstein Condensate of ⁴¹K is discussed and an evaluation of its properties as a coolant are analysed. Secondly, the creation of a triply degenerate Bose-Fermi-Fermi gas of ⁴¹K-⁴⁰K-⁶Li is presented. Simultaneous observation of Pauli Pressure and Bose Condensation in the triply degenerate gas is reported. In addition, interspecies Feshbach resonances between ⁴¹K-⁴⁰K and ⁶Li-⁴¹K are observed, opening the way to the study of a strongly interacting isotopic Bose-Fermi mixture of ⁴¹K-⁴⁰K, which have similar mass. Thirdly, the creation of a quantum degenerate Bose-Fermi mixture of ²³Na-⁴⁰K is discussed and over thirty Feshbach resonances are identified. Finally, a degenerate ²³Na-⁴⁰K Bose-Fermi mixture opens the way to creating fermionic NaK ground state molecules, which are known to be chemically stable and have a larger permanent electric dipole than KRb. This thesis concludes with a review of the molecular properties of NaK and explores the possibilities of bringing Feshbach molecules of NaK into the singlet rovibrational ground state.<br>by Ibon Santiago González.<br>S.M.
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Delehaye, Marion. "Mixtures of superfluids." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEE015/document.
Full textAbstract:
Les atomes froids sont des outils uniques pour sonder la physique de la matière quantique. Hautement contrôlables, les gaz de Bose et de Fermi ultrafroids sont des systèmes idéaux pour la simulation quantique et pour explorer des manifestations spectaculaires des effets quantiques, comme la superfluidité. Avec des gaz froids de 6Li et de 7Li, nous avons produit le premier mélange de superfluides bosonique-fermionique, et étudié ses propriétés en initiant un contre-flot entre les nuages de Bose et de Fermi (mode dipolaire). La vitesse critique de superfluidité a été mesurée dans le crossover BEC-BCS et elle est trouvée proche de la vitesse du son dans le gaz de Fermi. Nous comparons nos mesures avec des prédictions théoriques récentes. En élevant la température du mélange, nous avons aussi observé une synchronisation inattendue entre les mouvements des deux nuages, interprétée comme un effet Zénon induit par la dissipation. Finalement, ce mélange de bosons et de fermions offre la possibilité unique de créer un piège homogène pour le gaz de Fermi. En ajustant finement les interactions, nous proposons d’utiliser la répulsion entre les bosons et les fermions pour compenser la courbure du piège harmonique pour les fermions. Pour des fermions présentant une polarisation de spin, nous prédisons théoriquement l’existence d’un superfluide avec une structure en “coquille” et fournissons les premières indications expérimentales de l’observation de ce superfluide topologiquement original<br>Ultracold atoms are unique tools to probe the physics of quantum matter. Indeed, the high degree of tunability of ultracold Bose and Fermi gases makes them ideal systems for quantum simulation and for exploring macroscopic manifestations of quantum effects, such as superfluidity. In this work, we have realized the first Bose-Fermi superfluid mixture, with ultracold gases of 6Li and 7Li. The properties of the mixture are investigated by initiating a Bose-Fermi counterflow through their dipole modes. The superfluid critical velocity is measured in the BEC-BCS crossover, and is found close to the sound velocity of the Fermi gas near unitarity. We compare our findings to recent theoretical predictions. Raising the temperature of the mixture, we observe an unexpected synchronization of the motion of the two clouds, interpreted with a Zeno-like model induced by dissipation. Finally, this Bose-Fermi mixture offers the unique possibility to create a homogeneoustrap for the Fermi gas. By a fine tuning of the interactions, we propose to use the Bose-Fermi repulsion to compensate the curvature of the harmonic trap for fermions. For a spin-polarized Fermi gas in such a trap, we theoretically predict the existence of a superfluid with a shell structure and we provide first experimental evidence for this topologically new superfluid
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Sugawa, Seiji. "Strongly Correlated Quantum Phases in Ultracold Mixtures of Bosons and Fermions in an Optical Lattice." 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/157745.
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Posso, Trujillo Katerine [Verfasser]. "Theoretical study of the preparation of quantum degenerate mixtures for precision atom interferometry / Katerine Posso Trujillo." Hannover : Gottfried Wilhelm Leibniz Universität, 2018. http://d-nb.info/1161096906/34.
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Schulze, Torben Alexander [Verfasser]. "Quantum degenerate mixtures of 23Na-39K and coherent transfer paths in NaK molecules / Torben Alexander Schulze." Hannover : Gottfried Wilhelm Leibniz Universität, 2018. http://d-nb.info/116184547X/34.
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Ferrier-Barbut, Igor. "Mixtures of Bose and Fermi Superfluids." Thesis, Paris, Ecole normale supérieure, 2014. http://www.theses.fr/2014ENSU0012/document.
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On trouve des manifestations de la physique quantique au niveau thermodynamique dansde nombreux systèmes. Un exemple marquant est la superfluidité, découverte au début du20ème siècle, que l’on retrouve de l’hélium aux étoiles à neutrons. Les gaz dilués ultrafroidsoffrent une polyvalence unique pour étudier des systèmes quantiquesmacroscopiques, pouvant directement tester les théories grâce à un environnementcontrôlé. Dans cette thèse, nous présentons plusieurs études expérimentales de gaz froidsde lithium. Le lithium fournit la possibilité de réaliser des ensembles de bosons et defermions, avec des interactions contrôlables entre les constituants. Nous présentons lestechniques utilisées pour préparer et étudier des gaz dégénérés de lithium, et uneamélioration possible des méthodes existantes. Nous décrivons premièrement une étudede la recombinaison à trois bosons avec une interaction à deux corps résonante. Comparésquantitativement à la théorie, ces résultats fournissent une référence pour les étudesfutures du gaz de Bose unitaire. Pour finir, nous présentons la première observationexpérimentale d’un mélange de superfluides de Bose et de Fermi. Nous démontrons queles deux composants sont superfluides et que leur écoulement relatif vérifie les propriétésdes écoulement superfluides, avec une absence de viscosité en dessous d’une vitessecritique puis la présence de dissipation au-delà. En utilisant des excitations collectives dece mélange, nous mesurons l’interaction entre les deux superfluides, en accord avec unmodèle théorique<br>Manifestations of Quantum Physics at the thermodynamical level are found in a broadrange of physical systems. A famous example is superfluidity, discovered at the beginningof the 20th century and found in many different situations, from liquid helium to neutronstars. Dilute ultracold gases offer a unique versatility to engineer quantum many-bodysystems, which can be directly compared with theory thanks to the controllability of theirenvironment. In this thesis we present several experimental investigations led on ultracoldlithium gases. Lithium provides the possibility to study ensembles of bosons andfermions, with controllable interactions between the constituents. We present experimentaltechniques for preparation and studies of degenerate gases of lithium, with prospects forimprovement of the existing methods. We first report on an investigation of three-bodyrecombination of bosons under a resonant two-body interaction. This study, quantitativelycompared with theory constitutes a benchmark for further studies of the unitary Bose gas.Finally, we present the first experimental realization of a mixture of a Bose superfluid witha Fermi superfluid. We demon- strate that both components are in the superfluid regime,and that the counter-flow motion between them possesses the characteristics of superfluidflow, with the absence of viscosity below a critical velocity, and an onset of friction above.Using collective oscillations of the mixture, we measure the coupling between the twosuperfluids in close agreement with a theoretical model
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Cappellaro, Alberto. "Ultracold Quantum Gases: Beyond-Mean-Field Effects." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3426696.
Full textAbstract:
In this thesis we present a detailed investigation of the role played by quantum and thermal fluctuations in ultracold Bose gases. We begin with a review of several important concepts and analytical tools within a functional integration formalism. We first focus on the so-called zero-range approximation for the interaction potential, by recovering the Bogoliubov results and the Landau two-fluid model from a field-theory perspective. In deriving the beyond-mean-field equation of state, we are going to show that a crucial point concerns the proper regularization of the divergent zero-point energy. Among the alternative approaches to investigate finite-temperatures Bose gases, we apply the kinetic theory to explain some recent results on the sound propagation in two-dimensional Bose gases.
We then move to consider the eventual corrections to the thermodynamics of Bose gases due to the finite-range character of the interaction potential. The coupling constants of the finite-range model are related to measurable scattering parameters through an effective-field-theory approach. The role of finite-range corrections is considered not only in three spatial dimensions but also in systems with lower dimensionalities. Our analytical predictions are in good agreement with available Monte Carlo simulations and consistent with other theoretical frames, as the Lieb-Lininger theory for one-dimensional systems.
In the third chapter, the relevance of fluctuations is investigated from an alternative point of view. Indeed, for a single-component Bose gas we have actually considered their effect as deviations of thermodynamic quantities from the mean-field and zero-range picture. In the case of collapsing Bose mixtures, we are going to show that zero-temperature fluctuations play a crucial stabilizing role against the collapse instability. Because of this peculiar mechanism, ultracold mixtures can display finite-density configurations also in free space. Inspired by recent experiments, we characterize this novel self-bound state by comparison with bright solitons, following a variational scheme. We also consider the case of binary mixtures where a coherent internal coupling is turned on.
In the last chapter, we move to deal with dipolar condensates. In particular, we are interested in beyond-mean-field effects leading to the formation of inhomogeneous ground states. In order to provide a reliable answer to the open issue of superfluid properties of these structures, we present our recent numerical investigation on the phase diagram of dipolar bosons.<br>In this thesis we present a detailed investigation of the role played by quantum and thermal fluctuations in ultracold Bose gases. We begin with a review of several important concepts and analytical tools within a functional integration formalism. We first focus on the so-called zero-range approximation for the interaction potential, by recovering the Bogoliubov results and the Landau two-fluid model from a field-theory perspective. In deriving the beyond-mean-field equation of state, we are going to show that a crucial point concerns the proper regularization of the divergent zero-point energy. Among the alternative approaches to investigate finite-temperatures Bose gases, we apply the kinetic theory to explain some recent results on the sound propagation in two-dimensional Bose gases.
We then move to consider the eventual corrections to the thermodynamics of Bose gases due to the finite-range character of the interaction potential. The coupling constants of the finite-range model are related to measurable scattering parameters through an effective-field-theory approach. The role of finite-range corrections is considered not only in three spatial dimensions but also in systems with lower dimensionalities. Our analytical predictions are in good agreement with available Monte Carlo simulations and consistent with other theoretical frames, as the Lieb-Lininger theory for one-dimensional systems.
In the third chapter, the relevance of fluctuations is investigated from an alternative point of view. Indeed, for a single-component Bose gas we have actually considered their effect as deviations of thermodynamic quantities from the mean-field and zero-range picture. In the case of collapsing Bose mixtures, we are going to show that zero-temperature fluctuations play a crucial stabilizing role against the collapse instability. Because of this peculiar mechanism, ultracold mixtures can display finite-density configurations also in free space. Inspired by recent experiments, we characterize this novel self-bound state by comparison with bright solitons, following a variational scheme. We also consider the case of binary mixtures where a coherent internal coupling is turned on.
In the last chapter, we move to deal with dipolar condensates. In particular, we are interested in beyond-mean-field effects leading to the formation of inhomogeneous ground states. In order to provide a reliable answer to the open issue of superfluid properties of these structures, we present our recent numerical investigation on the phase diagram of dipolar bosons.
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Salez, Thomas. "Towards quantum degenerate atomic Fermi mixtures : design of the experiment and magnetic transport of lithium 6 - potassium 40." Paris 6, 2011. http://www.theses.fr/2011PA066403.
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Au cours de cette thèse, j'ai participé au montage complet d'une expérience visant à refroidir et manipuler deux espèces atomiques alcalines fermioniques, 6Li et 40K. Le dispositif expérimental a pour objectifs l'étude des mélanges de fermions ultra-froids de masses différentes et la réalisation d'un simulateur analogique quantique versatile. Lors de sa conception, nous avons assemblé une enceinte à ultra-vide, réalisé un système laser stabilisé complet pour chaque espèce et mis en place deux sources atomiques performantes, un ralentisseur Zeeman de 6Li et un piège magnéto-optique bidimensionnel de 40K; la plupart des grandeurs optiques et électriques ainsi que les diagnostiques d'imagerie étant contrôlés par voie informatique. Ces premières étapes ont permis l'obtention d'un piège magnéto-optique à deux espèces performant, contenant typiquement 5x10^9 atomes de 6Li et 8x10^9 atomes de 40K. Dans cette configuration, nous avons produit les premières molécules hétéronucléaires de 6Li40K* par photo-association, pour lesquelles nous avons observé et identifié 70 raies rovibrationnelles. Dans une seconde partie, je décris en détail le transport magnétique du mélange atomique entre la cellule du piège magnéto-optique et une cellule d'expérience, où règne un vide poussé et bénéficiant d'un grand accès optique. Ce dispositif complet, de sa conception à son optimisation expérimentale, en passant par son assemblage mécanique et la mise en place de diagnostiques numériques, fait partie intégrante de mon travail. Son efficacité a pu être testée et optimisée, permettant ainsi un transfert performant du mélange vers la cellule finale
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Simeni, Simeni Marien. "Quantum cascade laser absorption studies of nitric oxide production by nanosecond pulsed discharges in air and in combustible mixtures." Thesis, Châtenay-Malabry, Ecole centrale de Paris, 2015. http://www.theses.fr/2015ECAP0033/document.
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Les plasmas d’air à pression atmosphérique ont de nombreuses applications. Nous pouvons par exemple citer les applications biomédicales, le traitement des matériaux, la bio-décontamination environnementale et la combustion assistée par plasma. La polyvalence des décharges plasma résulte de leur capacité à produire des densités élevées d’espèces actives, sans toutefois chauffer substantiellement le gaz. Les décharges nanosecondes répétitivement pulsées (NRP) ont particulièrement reçu une grande attention en raison de leur capacité à produire des densités électroniques élevées, qui conduisent à la création de fortes densités d’espèces actives telles que l’oxygène atomique (O). Par ailleurs, des mesures de spectroscopie d’émission ont montré que des états excités du monoxyde d’azote (NO) sont produits par les décharges NRP opérant dans l’air ou dans des mélanges combustibles. Bien que les décharges NRP aient déjà fait l’objet de plusieurs investigations, les mécanismes cinétiques conduisant à la production de NO sont toujours incertains. C’est la motivation première des travaux menés dans le cadre de cette thèse. En outre, les décharges NRP se sont avérées produire une grande quantité d’oxygène d’atomique, espèce de grande importance pour la combustion assistée par plasma. Il a été en particulier démontré que grâce à la production élevée d’espèces actives, les décharges NRP peuvent stabiliser efficacement des flammes pauvres, à pression atmosphérique. Cependant la production de NO par les décharges NRP et les flammes stabilisées à l’aide des décharges NRP reste à étudier. Cela constitue le second objectif de cette thèse. Les mesures in-situ de densités absolues de NO dans les décharges plasmas et/ou en combustion sont très difficiles. Les techniques de fluorescence telle que la fluorescence induite par laser (LIF) nécessitent de complexes méthodes de calibration. Ces techniques requièrent également la connaissance des taux de quenching des états excités (en particulier à pression atmosphérique). Or ces taux de quenching sont très fortement dépendants de la température, de la nature des espèces en présence et de leur densité, et peuvent donc énormément différer entre un plasma opérant dans l’air et en combustion. D’autres techniques telles que l’utilisation des sondes à chimiluminescence sont tout aussi sujettes aux problèmes de calibration et de quenching des états excités tandis que les mesures ex-situ à l’aide d’analyseurs à gaz réalisant de l’absorption dans l’UV et l’IR peuvent conduire à des erreurs, surtout lorsqu’il s’agit de mesurer des radicaux. Dans cette étude, nous avons développé la spectroscopie d’absorption par laser à cascade quantique (QCLAS), pour des mesures in-situ de densités de NO dans l’air et en combustion. Cette technique permet de surmonter les difficultés des autres méthodes par utilisation d’une spectroscopie rotationnelle-vibrationnelle de haute résolution spectrale (10-3 cm-1). La QCLAS a les avantages d’être spectralement sélective, d’avoir une grande sensibilité et de ne pas nécessiter de calibration. Deux dispositifs expérimentaux ont été développés pour mesurer des densités de NO et des températures (1) dans une décharge NRP dans l’air, avec une résolution spatiale de 300-µm, et (2) en aval de la décharge NRP opérant dans l’air et dans des flammes méthane/air assistée par plasma, par utilisation d’une cellule multi-passages. [...]<br>Atmospheric pressure plasmas have numerous potential applications. These applications include for instance biomedicine, material processing, environmental biodecontamination and plasma-assisted combustion. The versatility of plasma discharges results from their ability to produce high quantities of active species without increasing the temperature of the gas appreciably. Nanosecond Repetitively Pulsed discharges (NRP) have received great attention owing to their capacity to generate high electron densities, which lead to the creation of a high density of active species such as atomic oxygen. Optical Emission Spectroscopy (OES) showed that excited nitric oxide (NO) was released by NRP discharges in air or in air/fuel mixtures.Although NRP discharges have already been the object of several investigations, the kinetic mechanisms of NO production by NRP discharges at atmospheric pressure remain somewhat unclear. This is one of the motivations for the investigations conducted in this thesis. In addition, NRP discharges were found to produce large amounts of atomic oxygen, which is of great interest for applications such as plasma-assisted combustion. It was shown in particular that thanks to this high production of active species, NRP discharges can effectively stabilize lean flames at atmospheric pressure. However, the production of NO in NRP discharges and in plasma-stabilized flames remains to be investigated. This is the second purpose of this thesis.Absolute and in-situ NO density measurements in atmospheric pressure plasma or/and flame environments are very challenging. Fluorescence-based techniques such as Laser Induced Fluorescence (LIF) require complex calibration methods. These techniques also require the knowledge of the quenching rates of the excited states (particularly at atmospheric pressure), which strongly depend on the temperature, density and nature of the species and can be very different for plasma or/and flame environments. Other techniques, such as chemiluminescence probe sampling also have quenching and calibration issues, and ex-situ UV and IR absorption-based gas analyzers can lead to errors, in particular for radicals.In this study, we developed Quantum Cascade Laser Absorption Spectroscopy (QCLAS) for in-situ nitric oxide absolute density measurements in open-air and in combustion environments. This technique overcomes the difficulties of the previous ones by using high-resolution (10-3 cm-1) rotational-vibrational absorption spectroscopy. This technique presents the advantages of high spectral selectivity, no calibration requirement, and high sensitivity. Two experimental setups were developed to measure NO densities and temperature, (1) within a NRP discharge in air, with 300-µm spatial resolution, and (2) downstream of NRP discharges in air and in plasma-assisted methane/air flames, using multi pass cell. [...]
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Virtanen, T. (Timo). "Numerical calculations of quasiparticle dynamics in a Fermi liquid." Doctoral thesis, Oulun yliopisto, 2011. http://urn.fi/urn:isbn:9789514293900.
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Abstract
The problem of describing a system of many interacting particles is one of the most fundamental questions in physics. One of the central theories used in condensed matter physics to address the problem is the Fermi liquid theory developed by L. D. Landau in the 1956. The theory describes interacting fermions, and can be used to explain transport phenomena of electrons in metals and dynamics of helium three. Even when the theory is not directly applicable, it forms a basis against which other, more sophisticated theories can be compared.
this thesis the Fermi liquid theory is applied to 3He-4He-mixtures at temperatures where the bosonic 4He part is superfluid, and the mechanical properties of the system are largely determined by the 3He component, treated as a degenerate normal Fermi liquid. The dynamics of strongly interacting liquid 3He can be described as a collection of quasiparticles, elementary excitations of the system, which interact only weakly. In 3He-4He mixtures the interactions can be continuously tuned by changing the temperature and the concentration of the mixture. The scattering time of quasiparticles depends on temperature, and thus the transition from the hydrodynamic limit of continuous collisions at higher temperatures to the collisionless ballistic limit at low temperatures can be studied. This gives invaluable information on the role of the interactions in the dynamics of the system.
In this work, by using the Fermi liquid theory and Boltzmann transport equation, the dynamics of helium mixture disturbed by a mechanical oscillator is described in the full temperature range. The solution necessarily is numeric, but new analytical results in the low temperature limit are obtained as well. The numerical approach enables one to study various boundary conditions thoroughly, and allows application of the theory to a specic geometry. It is shown that in order to explain the experimental observations, it is necessary to take into account the reflection of quasiparticles from the walls of the container. For suitable choice of oscillator frequency and container size, second sound resonances are observed at higher temperatures, while in the ballistic limit quasiparticle interference can be seen.
The numerical results are in quantitative agreement with experiments, thus attesting the accuracy of Fermi liquid theory. In particular, the previously observed decrease of inertia of a mechanical oscillator immersed in helium at low temperatures is reproduced in the calculations, and is explained by elasticity of the fluid due to Fermi liquid interactions.
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Aidoudi, Farida Himeur. "Extending ionothermal synthesis." Thesis, University of St Andrews, 2012. http://hdl.handle.net/10023/2592.
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An exploration of some organic-inorganic hybrid metal fluorides and lanthanide containing metal organic frameworks (Ln-MOFs) has been carried out under ionothermal conditions. In this synthesis technique an ionic liquid (IL) or deep eutectic mixture (DES) is used as the solvent and in many cases as the provider of the organic structure directing agent. A wide range of ILs and DESs have been investigated as the reaction solvent for the synthesis of organically templated vanadium fluorides and oxyfluorides (VOFs), and initially this has proved to be successful with the isolation of 13 phases, including eight new materials. In the VOFs synthesis the IL acts as a solvent, however the DES acts as a solvent and also as a template delivery agent, where the expected template is provided by the partial breakdown of the urea derivative component. Interestingly, it has been shown that the same structure can be accessible via two different ways; either by using IL with an added templating source, or simply through the use of a DES without any other additive; since the template is provided by the in situ breakdown of the DES. The synthesis of VOFs with extended structures was achieved by the use of the hydrophobic IL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM Tf₂N) as the solvent. [HNC₅H₅][V₂O₂F₅] represents the first VOF with a 2D network that contains exclusively V⁴⁺. This material may be considered as arising via condensation of the previously known ladder-like chains. Furthermore, using imidazole as an added template has produced another layer material that has significant similarities to the [HNC₅H₅][V₂O₂F₅] structure, but with some key differences. Within the same system three other phases were also isolated, including two novel materials displaying the known ladder-type building units. Further investigations in the ionothermal synthesis of VOF using EMIM Tf₂N resulted in a successful synthesis of [NH₄]₂[HNC₇H₁₃][V₇O₆F₁₈], a novel material displaying a unique double layered topology featuring a S = ½ kagome type lattice of V⁴⁺ ions (d¹). Two of the V⁴⁺ based kagome sheets are pillared by V³⁺ ions to form a double layered structure templated by both ammonium and quinuclidinium cations. This compound exhibits a high degree of magnetic frustration, with significant antiferromagnetic interactions but no long range ordering was observed above 2 K. This material presents an interesting comparison to the famous Herbertsmithite, ZnCu₃(OH)₆Cl₂, and may provide an excellent candidate for realising a quantum spin liquid (QSL) ground state. Interestingly, in this system the use of EMIM Tf₂2N as a solvent produces mainly V⁴⁺-containing materials, despite the high reaction temperature (170 °C). This characteristic is unprecedented in VOFs synthesis, as rising the reaction temperature above 150 °C in other techniques (i.e. hydrothermal synthesis) would often result in further reduction of V⁴⁺ to V³⁺. Using the ionothermal technique in the synthesis of hybrid iron fluorides resulted in the isolation of three chain-type materials. Again, the IL acts as the solvent and the DES acts as the solvent and also as the template provider where the expected template is released by the partial breakdown of the urea derivative component of the DES. The synthesis of Ln-MOF using a choline chloride/ 1,3-dimethylurea deep eutectic mixture has produced three novel isostructural materials. Usually, in ionothermally prepared materials (i.e. zeolites) the urea portion of the DES is unstable and breaks down in situ to form ammonium or alkylammonium cations. In the ionothermal synthesis of Ln-MOF, 1,3-dimethyurea (DMU) remains intact and is occluded in the final structure. Using a choline chloride/ethylene glycol deep eutectic solvent led to the isolation of a Ln-MOF with interesting structural properties, however none of the DES components appeared in the final structure. These results demonstrate once more the usefulness and applicability of the ionothermal synthesis method and emphasise how this synthesis technique can be further extended and applied in the preparation of important structures with unique properties and functionalities.
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Kretzschmar, Norman. "Experiments with Ultracold Fermi Gases : quantum Degeneracy of Potassium-40 and All-solid-state Laser Sources for Lithium." Thesis, Paris, Ecole normale supérieure, 2015. http://www.theses.fr/2015ENSU0012/document.
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Cette thèse présente de nouvelles techniques pour l'étude expérimentale des gaz quantique ultrafroids d'atomes fermioniques de lithium et de potassium. Dans la première partie de cette thèse, nous décrivons la conception et la caractérisation des nouveaux composants de notre dispositif expérimental capable de piéger et refroidir simultanément des atomes de $^6$Li et de $^{40}$K à des températures ultrabasses. Nous rendons compte d'une nouvelle technique de refroidissement sub-Doppler, reposant sur la transition de la raie D$_1$ des atomes alcalins, pour refroidir des atomes de lithium et de potassium par laser. Après cette étape de mélasse, nous avons mesuré une densité dans l'espace des phases de l'ordre de $10^{-4}$ à la fois pour le $^6$Li et le $^{40}$K. Nous présentons le refroidissement par évaporation forcée d'atomes de $^{40}$K qui commence dans un piège magnétique quadripolaire pluggé et continue dans un piège optique dipolaire. Dans ce contexte, nous rendons compte de la production d'un gaz quantique de Fermi dégénéré de $1.5\times10^5$ atomes de $^{40}$K dans un piège dipolaire croisé avec $T/T_{_F} = 0.17$, ce qui ouvre la voie à l'étude des superfluides de $^{40}$K en interaction forte. Dans la deuxième partie de cette thèse, nous présentons une source laser à état solide, de faible largeur spectrale et capable d'émettre 5.2 W de puissance autour de 671 nm, dans la gamme des longueurs d'onde des transitions de la raie D du lithium. La source repose sur un laser en anneau pompé par diode, émettant sur la transition à 1342 nm de Nd:YVO$_4$, capable de produire 6.5 W de lumière dans un faisceau monomode limité par la diffraction. Nous rendons compte de trois différentes approches pour la génération de seconde harmonique du faisceau de sortie, à savoir en utilisant une cavité amplificatrice comprenant un cristal ppKTP, par doublage de fréquence intracavité et par un structure de guide d'onde de ppZnO:LN<br>This thesis presents novel techniques for the experimental study of ultracold quantum gases of fermionic lithium and potassium atoms. In the first part of this thesis, we describe the design and characterization of the new components of our experimental apparatus capable of trapping and cooling simultaneously $^6$Li and $^{40}$K atoms to ultracold temperatures. We report on a novel sub-Doppler cooling mechanism, operating on the D$_1$ line transition of alkali atoms, for laser cooling of lithium and potassium. The measured phase space densities after this molasses phase are on the order of $10^{-4}$ for both $^6$Li and $^{40}$K. We present the forced evaporative cooling of $^{40}$K atoms, starting in an optically plugged magnetic quadrupole trap and continuing in an optical dipole trap. In this context, we report on the production of a quantum degenerate Fermi gas of $1.5\times10^5$ atoms $^{40}$K in a crossed dipole trap with $T/T_{_F} = 0.17$, paving the way for the study of strongly interacting superfluids of $^{40}$K. In the second part of this thesis, we present a narrow-linewidth, all-solid-state laser source, emitting 5.2 W in the vicinity of the lithium D-line transitions at 671 nm. The source is based on a diode-end-pumped unidirectional ring laser operating on the 1342 nm transition of Nd:YVO$_4$, capable of producing 6.5 W of single-mode light delivered in a diffraction-limited beam. We report on three different approaches for second-haromonic generation of its output beam, namely by employing an enhancement cavity containing a ppKTP crystal, intracavity frequency doubling and a ppZnO:LN waveguide structure
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Decamp, Jean. "Symétries et corrélations dans les gaz quantiques fortement interagissants à une dimension." Thesis, Université Côte d'Azur (ComUE), 2018. http://www.theses.fr/2018AZUR4060/document.
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L’objectif principal de cette thèse est l’étude théorique de mélanges quantiques fortement interagissants à une dimension et soumis à un potentiel externe harmonique. De tels systèmes fortement corrélés peuvent être réalisés et testés dans des expériences d’atomes ultrafroids. Leurs propriétés de symétrie par permutation non triviales sont étudiées, ainsi que leurs effets sur les corrélations. Exploitant une solution exacte pour des interactions fortes, nous extrayons des propriétés générales des corrélations encodées dans la matrice densité à un corps et dans les distributions des impulsions associées, dans les mélanges fermioniques et de Bose-Fermi. En particulier, nous obtenons des résultats substantiels sur le comportement à courtes distances, et donc les queues à haute impulsions, qui suivent des lois en k^−4 typiques. Les poids de ces queues, dénotés contacts de Tan, sont liés à de nombreuses propriétés thermodynamiques des systèmes telles que les corrélations à deux corps, la dérivée de l’énergie par rapport à la longueur de diffusion unidimensionnelle, ou le facteur de structure statique. Nous montrons que ces contacts universels de Tan permettent également de caractériser la symétrie spatiale des systèmes, et constituent donc une connexion profonde entre les corrélations et les symétries. En outre, la symétrie d’échange est extraite en utilisant une méthode de théorie des groupes, à savoir la méthode de la somme des classes (class-sum method en anglais), qui provient à l’origine de la physique nucléaire. De plus, nous montrons que ces systèmes suivent une version généralisée du fameux théorème de Lieb-Mattis. Souhaitant rendre nos résultats aussi pertinents expérimentalement que possible, nous dérivons des lois d’échelle pour le contact de Tan en fonction de l’interaction, de la température et du confinement transverse. Ces lois présentent des effets intéressants liés aux fortes corrélations et à la dimensionnalité<br>The main focus of this thesis is the theoretical study of strongly interacting quantum mixtures confined in one dimension and subjected to a harmonic external potential. Such strongly correlated systems can be realized and tested in ultracold atoms experiments. Their non-trivial permutational symmetry properties are investigated, as well as their interplay with correlations. Exploiting an exact solution at strong interactions, we extract general correlation properties encoded in the one-body density matrix and in the associated momentum distributions, in fermionic and Bose-Fermi mixtures. In particular, we obtain substantial results about the short-range behavior, and therefore the high-momentum tails, which display typical k^−4 laws. The weights of these tails, denoted as Tan’s contacts, are related to numerous thermodynamic properties of the systems such as the two-body correlations, the derivative of the energy with respect to the one-dimensional scattering length, or the static structure factor. We show that these universal Tan’s contacts also allow to characterize the spatial symmetry of the systems, and therefore is a deep connection between correlations and symmetries. Besides, the exchange symmetry is extracted using a group theory method, namely the class-sum method, which comes originally from nuclear physics. Moreover, we show that these systems follow a generalized version of the famous Lieb-Mattistheorem. Wishing to make our results as experimentally relevant as possible, we derive scaling laws for Tan’s contact as a function of the interaction, temperature and transverse confinement. These laws. Display displadisplay display interesting effects related to strong correlations and dimensionality
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Ota, Miki. "Sound propagation in dilute Bose gases." Doctoral thesis, Università degli studi di Trento, 2020. http://hdl.handle.net/11572/250493.
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In this doctoral thesis, we theoretically investigate the propagation of sound waves in dilute Bose gases, in both the collisionless and hydrodynamic regimes. The study of sound wave is a topic of high relevance for the understanding of dynamical properties of any fluid, classical or quantum, and further provides insightful information about the equation of state of the system. In our work, we focus in particular on the two-dimensional (2D) Bose gas, in which the sound wave is predicted to give useful information about the nature of the superfluid phase transition. Recently, experimental measurement of sound wave in a uniform 2D Bose gas has become available, and we show that the measured data are quantitatively well explained by our collisionless theory. Finally, we study the mixtures of weakly interacting Bose gases, by developing a beyond mean-field theory, which includes the effects of thermal and quantum fluctuations in both the density and spin channels. Our new theory allows for the investigation of sound dynamics, as well as the fundamental problem of phase- separation.
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Mangaud, Etienne. "Dynamique quantique de transferts d'électron dans des systèmes environnés à fort couplage." Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30077/document.
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Les transferts d'électron sont au cœur de nombreux processus d'intérêts chimiques, biologiques ou photochimiques comme, par exemple, dans la technologie du photovoltaïque ou la photosynthèse où ils ne sont que rarement isolés. Par ailleurs, des résultats expérimentaux tendent à montrer que les phénomènes quantiques, notamment les superpositions d'états ou cohérences, peuvent se maintenir sur l'échelle de temps du transfert d'électron même en présence d'un environnement. Dans ce travail, le transfert d'électron est étudié dans trois types de systèmes moléculaires. Le premier est un transfert intermoléculaire dans une hétérojonction oligothiophène-fullerène modélisant une interface de séparation de charge pour de futures cellules photovoltaïques organiques. Le second est un transfert intramoléculaire dans des composés organiques à valence mixte où l'on étudie l'effet d'un pont avec une chaîne croissante de n-paraphénylènes dans des polymères aromatiques avec des sites donneur-accepteur (1,4-diméthoxy-3-méthylphénylènes). Le troisième est le transfert intermoléculaire dans une chaîne de tryptophanes dans une chromoprotéine cryptochrome. Dans tous ces cas, une attention particulière est portée à une modélisation réaliste. Dans ce contexte, il est crucial de faire une partition judicieuse entre l'ensemble des degrés de liberté et de décrire proprement l'interaction entre ceux impliqués dans le transfert et ceux qualifiés d'environnement. A cette fin, un hamiltonien décrivant un système électronique donneur-accepteur couplé à un bain d'oscillateurs harmoniques a été paramétré en utilisant notamment la méthode de la DFT contrainte (cDFT). Le bain d'oscillateurs a été décrit par une analyse en modes normaux ou via la fluctuation de l'écart énergétique obtenue par des calculs de type QM/MM. Les systèmes étudiés présentent tous des environnements fortement couplés et structurés nécessitant d'explorer des stratégies peu conventionnelles. Dans un modèle d'environnement formé d'un nombre fini d'oscillateurs traités explicitement, le traitement dynamique nécessite d'utiliser des méthodes multidimensionnelles telles que la méthode multi-couches multiconfigurationnelle de produits de Hartree dépendant du temps (ML-MCTDH). Dans l'approche de dynamique dissipative où le bain intervient seulement par ses propriétés statistiques il est alors nécessaire de se tourner vers une méthode non perturbative telle que les matrices hiérarchiques. A côté de ces approches exactes, une autre stratégie consiste à effectuer une transformation de coordonnées afin de définir une coordonnée collective incluse avec le système électronique qui est elle-même couplée à un bain secondaire. La propagation dynamique peut alors être effectuée par une équation-maîtresse approchée s'appuyant sur la théorie de perturbation. Comme principaux résultats, nous analysons en détail le domaine de validité des différentes méthodes utilisées puis expliquons le comportement dynamique des différents cas amenant à une délocalisation facile ou à un piégeage de la charge. Par là même, nous montrons que la méthodologie proposée, appliquée à des systèmes-modèles dans ce travail, est bien adaptée pour l'analyse de l'influence mutuelle entre le transfert de charge et les déformations nucléaires, une situation prototypique pour de nombreux processus importants dans les systèmes chimiques et biologiques<br>Electron transfer reactions are at stake in several chemical, biological or photochemical processes of great interest as, for instance, photovoltaic technology or photosynthesis where they are rarely isolated. Furthermore, experimental results show that quantum phenomena, notably superpositions of states or coherences, can persist on the time scale of the electron transfer even in the presence of an environment. In this work, electron transfer is studied in three types of molecular systems. The first one is an intermolecular transfer in an oligothiophene-fullerene heterojonction modelling a charge separation interface for future organic photovoltaic devices. The second one is an intramolecular transfer in mixed-valence organic compounds where the bridge effect of an increasing n-paraphenylens chain is studied on aromatic polymers with donor-acceptor sites (1-4,dimethoxy-3-methylphenylens). The third one is an intermolecular transfer in a tryptophan chain of a cryptochrome chromoprotein. In all these cases, a special attention is given to realistic modelling. In this context, it is crucial to define carefully the partition between the degrees of freedom, in particular amongst those implied in the transfer and those qualified to be part of an environment. To this end, a Hamiltonian describing a donor-acceptor electronic system coupled to a bath of harmonic oscillators is parameterized using the constrained DFT method (cDFT). The oscillators' bath is described by a normal mode analysis or via the electronic gap fluctuation obtained by QM/MM calculations. The systems under study turn out to be strongly coupled, and structured which requires to explore non-conventional strategies. In a model environment constituted of a finite number of oscillators treated explicitly, the dynamics is performed by multidimensional quantum propagation methods such as the multi-layer multiconfigurational time-dependent Hartree method (ML-MCTDH). In the dissipative approach, where the bath acts only by its statistical properties, it is mandatory to turn to non-perturbative methods such as the hierarchical equations of motion approach. Apart from these exact approaches, an alternative strategy consists in carrying out a change of coordinates in order to define a collective bath mode included in the electronic system, which itself is coupled to a secondary bath. The dynamical propagation can then be done by an approximated quantum master equation using perturbation theory. As main results, we show in detail the domain of validity of the different methods presented and explain the dynamical behaviour of the different cases leading to an easy delocalization or a trapping of the charge. Hence, we show that the methodology applied in model systems are well suited for the analysis of the mutual interplay between the charge transfer and nuclear deformations, a prototypical situation in many important chemical and biological processes
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Naulet, Zacharie. "Développement d'un modèle particulaire pour la régression indirecte non paramétrique." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLED057/document.
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Cette thèse porte sur les statistiques bayésiennes non paramétriques. La thèse est divisée en une introduction générale et trois parties traitant des aspects relativement différents des approches par mélanges (échantillonage, asymptotique, problème inverse). Dans les modèles de mélanges, le paramètre à inférer depuis les données est une fonction. On définit une distribution a priori sur un espace fonctionnel abstrait au travers d'une intégrale stochastique d'un noyau par rapport à une mesure aléatoire. Habituellement, les modèles de mélanges sont surtout utilisés dans les problèmes d'estimation de densités de probabilité. Une des contributions de ce manuscrit est d'élargir leur usage aux problèmes de régressions.Dans ce contexte, on est essentiellement concernés par les problèmes suivants:- Echantillonage de la distribution a posteriori- Propriétés asymptotiques de la distribution a posteriori- Problèmes inverses, et particulièrement l'estimation de la distribution de Wigner à partir de mesures de Tomographie Quantique Homodyne<br>This dissertation deals with Bayesian nonparametric statistics, in particular nonparametric mixture models. The manuscript is divided into a general introduction and three parts on rather different aspects of mixtures approaches (sampling, asymptotic, inverse problem). In mixture models, the parameter to infer from the data is a function. We set a prior distribution on an abstract space of functions through a stochastic integral of a kernel with respect to a random measure. Usually, mixture models were used primilary in probability density function estimation problems. One of the contributions of the present manuscript is to use them in regression problems.In this context, we are essentially concerned with the following problems :- Sampling of the posterior distribution- Asymptotic properties of the posterior distribution- Inverse problems, in particular the estimation of the Wigner distribution from Quantum Homodyne Tomography measurements
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Iftner, Christophe. "Modélisation de complexes et agrégats moléculaires en matrice cryogénique." Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30160/document.
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Cette thèse présente le développement et les applications d'un formalisme hybride quantique-classique pour décrire la structure électronique d'un système actif avec un environnement cryogénique (agrégat ou matrice d'atomes de gaz rare). La description quantique de la structure électronique du système actif est faite dans le cadre d'une approximation de type Liaisons Fortes de la Théorie de la Fonctionnelle de la Densité, avec charges atomiques autocohérentes (SCC-DFTB). L'environnement de gaz rare est décrit par des potentiels classiques atome-atome (FF). L'interaction entre le sytème actif et les atomes de l'environnement cryogénique est représentée par des opérateurs matriciels locaux anisotropes électron-atome, ainsi que par des contributions de polarisation et de dispersion. La détermination des opérateurs et des paramètres d'interaction est extraite de calculs ab initio post Hartree-Fock (CCSD-T) sur les paires atome actif/atome d'argon. Les applications concernent les interactions entre hydrocarbures, agrégats d'eau isolés ou complexes hydrocarbures/eau avec des agrégats et ou des matrices d'argon. Le modèle est validé sur de petits systèmes (molécule C6H6 , molécule H2O) en interaction avec des atomes et agrégats d'argon. Nous avons ainsi déterminé les données structurales et énergétiques pour les agrégats (C6H6)Arn (n < 55) qui ont été comparées à des données ab initio (DFT, CCSD-T) pour les plus petits agrégats, ou à des calculs de champ de force publiés dans la littérature pour les agrégats de plus grande taille. Le modèle permet également un traitement unifié de différentes situations électroniques permettant ainsi la détermination de l'évolution des potentiels d'ionisation du système actif en fonction de la taille n de l'agrégat solvatant. Le modèle DFTB/FF a ensuite été appliqué à des molécules et nano-agrégats d'eau (H2O)n (n=2-6) insérés dans des matrices d'argon, représentées par des sous-ensembles finis du réseau cristallin cubique faces centrées. Des données structurales et énergétiques ont été obtenues. Des études de dynamique moléculaire ont permis la détermination de spectres infrarouges (IR) à température finie. La comparaison des spectres IR théoriques caractérisant une molécule d'eau en matrice avec les données expérimentales nous a permis de valider l'approche DFTB/FF. Le cas de l'hexamère (H2O)6, plus petit agrégat présentant une structure tri-dimensionnelle et caractérisé par plusieurs isomères stables, a été étudié de façon exhaustive : l'effet de la matrice sur les structures de certains de ces isomères a été mis en évidence, ainsi que des effets différentiels sur leur stabilités respectives. Une influence sur les positions des bandes IR des agrégats a également été montrée. Les résultats obtenus permettent une interprétation satisfaisante des données expérimentales existantes pour les plus petits agrégats. L'assignation des spectres expérimentaux de l'hexamère demeure incertaine. Enfin, des résultats préliminaires sur les structures, l'énergétique et les spectres IR à température finie ont été obtenus pour des complexes d'Hydrocarbures Aromatiques Polycycliques avec l'eau (HAP-H2O) en matrices d'argon. L'ensemble des données obtenues pour ces complexes est discuté en relation avec les résultats expérimentaux en environnement cryogénique obtenus dans l'équipe de Joëlle Mascetti de l'Institut des Sciences Moléculaires de l'Université Bordeaux I, dans le cadre d'une collaboration ANR (ANR PARCS no 13-BS08-0005). Ce travail a bénéficié d'une allocation de thèse co-financée par l'Institut de Physique du CNRS et le Conseil Régional de la région Midi-Pyrénées<br>This thesis presents the development and applications of an hybrid quantum-classical formalism in order to describe the electronic structure of an active system in a cryogenic environment (cluster or rare gas matrix). The quantum description of the electronical structure of the active system is based on a a tight-binding approximation of the density functional theory, with self-consistency regarding the charges (SCC-DFTB). The rare gaz environment is described via classical atom-atom potential (FF). The interaction between the active system and the atoms of the cryogenic environment is represented by local anisotropic matricial electron-atom operators, as well as by polarisation and dispersion contributions. Operators and interaction parameters are extracted from post Hartree-Fock \textit{ab initio} calculations (CCSD-T) of active atom/argon atom pairs. The applications involve hydrocarbons, isolated water clusters or hydrocarbon/water complexes in interaction with argon clusters or matrices. The model has been validated on small systems (C6H6 molecule, H2O molecule) in interaction with argon atoms and clusters. We have been able to determine structural and energetic data for (C6H6)Arn (n < 55) clusters which are benchmarked against ab initio results (DFT,CCSD-T) for the smaller sizes, or with respect to FF calculations, available in the literature, for larger sized clusters. The model enables to treat various electronic situations, allows in particular to determine the evolution of the ionization potentials of the active system as a function of the inert cluster size. The SCC-DFTB/FF model has then been applied to water molecules and water nano-clusters (H2O)n (n=2-6) embedded in argon matrices, represented by finite size cristal pieces of the face centered cubic lattice. Structural and energetical data have been obtained. Molecular dynamics studies have enabled the determination of finite temperature infrared (IR) spectra. Comparison between the theoretical and experimental spectra of the water monomer embedded in the matrix validates the SCC-DFTB/FF approach. The case of the water hexamer (H2O)6, the smallest cluster presenting a three-dimensional structure and caracterized by several low-energy isomers, has been investigated exhaustively : the effect of the matrix on the structures of some isomers has been shown as well as differential effects on their respective stabilities. An influence on IR lines positions has also been highlighted. Our theoretical study allows for a satisfactory interpretation of the experimental data for the smallest clusters (n<4). The assignment of the experimental spectra of the hexamer remains in discussion. Finally, preliminary results on structures, energetics and finite temperature IR spectra have been obtained for Polycyclic Aromatic Hydrocarbons (PAH) /water complexes. The results for the complexes are discussed in relation with experimental data obtained in the team of Joëlle Mascetti at the Institute of Molecular Sciences (University of Bordeaux I), in the context of an ANR collaborative project (ANR PARCS no 13-BS08-0005). The thesis has been co-financed by the CNRS Institute of Physics and Conseil Regional of Region Midi-Pyrénées
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Costa, Marcello Ferreira da. "Dinâmica molecular de sistemas iônicos poliatômicos: modelos polarizável e não-polarizável." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/46/46132/tde-30062016-150459/.
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Simulações de sais de carbonato fundidos pelo método de Dinâmica Molecular (MD) foram efetuadas com o modelo polarizável de cargas flutuantes (FC). O modelo de cargas flutuantes implementa os efeitos de polarização pelo método de Lagrangiano estendido, onde as variáveis extras são as próprias cargas parciais do íon poliatômico. O modelo FC foi parametrizado por meio de cálculos ab inito, aplicado ao ânion carbonato. Cálculos de Química Quântica ab initio foram utilizados para corroborar o modelo proposto para o ânion carbonato. Os sistemas investigados consistem em misturas de carbonatos alcalinos fundidos, Li2CO3/K2CO3, os quais são utilizados como eletrólitos em células a combustível. As simulações MD foram utilizadas para verificar o efeito da polarização dos ânions sobre a estrutura e dinâmica do líquido. Estudamos o efeito da inclusão de polarização sobre a condutividade do eletrólito.<br>Simulations of molten carbonate salts by the method of Molecular Dynamics (MD) have been performed with the fluctuanting charge (FC) model. The FC model implements the effect of polarization by using method of extended Lagrangian, where the extra variables are the partial charges of the poliatomic ion. The FC model was parametrized by ab inito calculations os a single carbonate anion. Quantum Chemistry calculations bave been used to corroborate the model for the carbonate anion. The investigated systems consist of alkaline carbonate mixtures, Li2CO3/K2CO3, which are used as electrolytes in fuel cells. MD simulations have been used to verify polarization effects on structure and dynamics of the liquid. We study the effect of including anion polarization on the condutivity of the electrolyte.
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Lei, Weidong. "Cyclic Hoist Scheduling Problems in Classical and Sustainabl." Thesis, Belfort-Montbéliard, 2014. http://www.theses.fr/2014BELF0244/document.
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Les ateliers de traitement de surface automatisés, qui utilisent des robots de manutention commandés par ordinateur pour le transport de la pièce, ont été largement mis en place dans différents types d'entreprises industrielles, en raison de ses nombreux avantages par rapport à un mode de production manuel, tels que : une plus grande productivité, une meilleure qualité des produits, et l’impact sur les rythmes de travail. Notre recherche porte sur trois types de problèmes d'ordonnancement associés à ces systèmes, appelés Hoist Scheduling Problems, caractérisés par des contraintes de fenêtres de temps de traitement: (I) un problème à une seule ressource de transport où l’objectif est de minimiser le temps de cycle; (II) un problème bi-objectif avec une seule ressource de transport où il faut minimiser le temps de cycle et la consommation de ressources de traitement (et par conséquent le coût de production); et (III) un problème d'ordonnancement cyclique mono-objectif mais multi-robots.En raison de la NP-complétude des problèmes étudiés et de nombreux avantages de les outils de type quantum-inspired evolutionary algorithm (QEA), nous proposons d'abord un QEA hybride comprenant un mécanisme de décodage amélioré et une procédure réparation dédiée pour trouver le meilleur temps de cycle pour le premier problème. Après cela, afin d'améliorer à la fois la performance économique et environnementale qui constituent deux des trois piliers de la stratégie de développement durable de nos jours déployée dans de nombreuses industries, nous formulons un modèle mathématique bi-objectif pour le deuxième problème en utilisant la méthode de l'intervalle interdit. Ensuite, nous proposons un QEA bi-objectif couplé avec une procédure de recherche locale pour minimiser simultanément le temps de cycle et les coûts de production, en générant un ensemble de solutions Pareto-optimales pour ce problème. Quant au troisième problème, nous constatons que la plupart des approches utilisées dans les recherches actuelles, telles que la programmation entière mixte (MIP), peuvent conduire à l’obtention d’une solution non optimale en raison de la prise en compte courante d’une hypothèse limitant l’exploration de l’espace de recherche et relative aux mouvements en charge des robots. Par conséquent, nous proposons une approche de MIP améliorée qui peut garantir l'optimalité des solutions obtenues pour ce problème, en relaxant l'hypothèse mentionnée ci-dessus.Pour chaque problème, une étude expérimentale a été menée sur des cas industriels ainsi que sur des instances générées aléatoirement. Les résultats obtenus montrent que l’efficacité des algorithmes d'ordonnancement proposés, ce qui justifie les choix que nous avons faits<br>Automated treatment surface facilities, which employ computer-controlled hoists for part transportation, have been extensively established in various kinds of industrial companies, because of its numerous advantages over manual system, such as higher productivity, better product quality, and reduced labor intensity. Our research investigates three typical hoist scheduling problems with processing time windows in treatment surface facilities, which are: (I) cyclic single-hoist scheduling problem to minimize the cycle time; (II) cyclic single-hoist scheduling problem to minimize the cycle time and processing resource consumption (and consequently production cost); and (III) cyclic multi-hoist scheduling problem to minimize the cycle time.Due to the NP-completeness of the studied problems and numerous advantages of quantum-inspired evolutionary algorithm (QEA), we first propose a hybrid QEA with improved decoding mechanism and repairing procedure to find the best cycle time for the first problem. After that, to enhance with both the economic and environmental performance, which constitute two of the three pillars of the sustainable strategy nowadays deployed in many industries, we formulate a bi-objective mathematical model for the second problem by using the method of prohibited interval. Then we propose a bi-objective QEA with local search procedure to simultaneously minimize the cycle time and production cost, and we find a set of Pareto-optimal solutions for this problem. As for the third problem, we find that most existing approaches, such as mixed integer programming (MIP) approach, may identify a non-optimal solution to be an optimal one due to an assumption related to the loaded hoist moves which is made in many existing researches. Consequently, we propose an improved MIP approach for this problem by relaxing the above-mentioned assumption. Our approach can guarantee the optimality of its obtained solutions.For each problem, experimental study on industrial instances and random instances has been conducted. Computational results demonstrate that the proposed scheduling algorithms are effective and justify the choices we made
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Breidenich, Jennifer L. "Impact-initiated combustion of aluminum." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54403.
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This work focuses on understanding the impact-initiated combustion of aluminum powder compacts. Aluminum is typically one of the components of intermetallic-forming structural energetic materials (SEMs), which have the desirable combination of rapid release of thermal energy and high yield strength.
Aluminum powders of various sizes and different levels of mechanical pre-activation are investigated to determine their reactivity under uniaxial stress rod-on-anvil impact conditions, using a 7.62 mm gas gun. The compacts reveal light emission due to combustion upon impact at velocities greater than 170 m/s. Particle size and mechanical pre-activation influence the initiation of aluminum combustion reaction through particle-level processes such as localized friction, strain, and heating, as well as continuum-scale effects controlling the amount of energy required for compaction and deformation of the powder compact during uniaxial stress loading. Compacts composed of larger diameter aluminum particles (~70µm) are more sensitive to impact initiated combustion than those composed of smaller diameter particles. Additionally, mechanical pre-activation by high energy ball milling (HEBM) increases the propensity for reaction initiation.
Direct imaging using high-speed framing and IR cameras reveals light emission and temperature rise during the compaction and deformation processes. Correlations of these images to meso-scale CTH simulations reveal that initiation of combustion reactions in aluminum powder compacts is closely tied to mesoscale processes, such as particle-particle interactions, pore collapse, and particle-level deformation. These particle level processes cannot be measured directly because traditional pressure and velocity sensors provide spatially averaged responses. In order to address this issue, quantum dots (QDs) are investigated as possible meso-scale pressure sensors for probing the shock response of heterogeneous materials directly. Impact experiments were conducted on a QD-polymer film using a laser driven flyer setup at the University of Illinois Urbana-Champaign (UIUC). Time-resolved spectroscopy was used to monitor the energy shift and intensity loss as a function of pressure over nanosecond time scales. Shock compression of a QD-PVA film results in an upward shift in energy (or a blueshift in the emission spectra) and a decrease in emission intensity. The magnitude of the shift in energy and the drop in intensity are a function of the shock pressure and can be used to track the particle scale differences in the shock pressure. The encouraging results illustrate the possible use of quantum dots as mesoscale diagnostics to probe the mechanisms involved in the impact initiation of combustion or intermetallic reactions.
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Nagle, Julien. "Etude physique du laser a puits quantique." Paris 6, 1987. http://www.theses.fr/1987PA066549.
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L'approche experimentale choisie consiste a etudier les proprietes spectroscopiques de l'emission spontanee et stimulee pour des composants deja realises. Parallelement, un modele realiste a ete elabore dont la nouveaute reside dans l'inclusion explicite des effets de la densite d'etats de la cavite optique. L'accord est excellent pour les lasers gaas/algaas; l'inclusion des courants associes a la recombinaison dans la cavite permet d'expliquer la superiorite des lasers grinsch sur les lasers sch. Des structures optimisees sont presentees pour les lasers a puits quantiques avec zone active en gainas. Les difficultes rencontrees dans ce systeme tiennent a l'effet auger et aux courants de cavite. D'autre part il persiste dans ce systeme des problemes d'elaboration du materiau et des interfaces auxquels les structures laser a puits quantiques sont plus sensibles que les structures dh traditionnelles a zone active large
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Valloggia, Sylvie. "SPECTROSCOPIE DE PHOTOLUMINESCENCE LOCALE DANS LES SEMICONDUCTEURS MASSIFS (Si, InP) ET LES PUITS QUANTIQUES (GaAs/GaAlAs)." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37619041b.
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DUPONT-NIVET, ERIC. "Epitaxie en phase vapeur aux organometalliques de gainp et algainp sur gaas : application a la realisation de diodes et de lasers a heterojonctions." Paris 7, 1987. http://www.theses.fr/1987PA077108.
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Principes de base de la methode movpe et problemes poses par sa mise en oeuvre. Cas particuliers de gainp et de algainp. Analyse des mecanismes de la methode movpe. Proprietes des interfaces gainp/gaas, algainp/gaas et algainp/gainp et presentation de puits quantiques algainp/gainp. Realisation de dispositifs optoelectroniques: presentations de diodes electroluminescentes a homojonctions en gainp et algainp, examen des travaux des principales equipes epitaxiant algainp, presentation de lasers a heterojonctions algainp/gainp/algainp
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Brum, José Antonio. "Etude theorique des proprietes electroniques des heterostructures de semiconducteurs." Paris 7, 1987. http://www.theses.fr/1987PA077006.
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Relations de dispersion des porteurs dans le plan des couches, avec attention particuliere aux sous-bandes de valence issues des extrema gamma ::(8) des materiaux hotes; etude des problemes coulombiens avec resolution du probleme de l'exciton et etude de la raie d'emission associee aux recombinaisons electron-trou piege dans les puits quantiques gaas/algaas. Effets d'un champ electrique longitudinal sur les niveaux d'energie a une et deux particules; interpretations de la stabilite de l'exciton et etude des niveaux d'energie d'impurete et des super reseaux "dents de scie". Etude de la capture des porteurs depuis le continuum vers les etats lies du puits quantique (emission de phonon ou niveau-relais quasidiscret). Niveaux d'energie dans les fils quantiques
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Maurel, Philippe. "Contribution a l'etude des proprietes physiques des composes ga : :(x)in::(1-x)as::(y)p::(1-y) obtenus par croissance en phase vapeur par la methode des organometalliques." Paris 6, 1987. http://www.theses.fr/1987PA066517.
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Etude des proprietes electriques et optiques a basse temperature dans inp de haute purete. Observation de l'effet hall quantique par etude detaillee de proprietes de transport des porteurs bidimensionnels a l'heterojoncion, a dopage module de type p ou n dans inp/ga::(0,47) in::(0,53) as et inp/ga::(0,25) in::(0,75) as::(0,5) p::(0,5). Etude des proprietes structurelles et optiques des puits quantiques multiples inp/ga::(0,47) in::(0,53) as
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Moroni, Didier. "Etude des proprietes optiques de semi-conducteurs composes iii-v et de puits quantiques par photoluminescence et excitation de la photoluminescence." Paris 6, 1987. http://www.theses.fr/1987PA066540.
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Identification des types de recombinaison entre 2 et 300k dans les couches epaisses de gainas et gainp epitaxiees sur leur support respectif inp et gaas. Etude de l'origine de la luminescence et variation en fonction de l'epaisseur du taux de capture des porteurs de la barriere dans les puits quantiques ingaas/inp. Determination du coefficient d'interdiffusion de al et ga aux interfaces dans les puits quantiques gaas/gaalas
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Erman, Marko. "L'éllipsométrie spectroscopique à haute résolution latérale : modélisation, application aux surfaces, interfaces et puits quantiques dans le matériaux semi-conducteur III-V." Paris 6, 1986. http://www.theses.fr/1986PA066400.
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Etude théorique et expérimentale de l'application de la méthode aux semi-conducteurs III-V et en particulier à l'analyse des interfaces. Etude des systèmes GaAlAs/GaAs et GaInAs/InP. Détermination simultanée de l'épaisseur des couches et de l'énergie de localisation pour les différentes transitions optiques, dans le cas de puits quantiques et de super-réseaux; effets dus au couplage entre les puits quantiques. Obtention de cartographies avec une résolution optique de 10mu m. Le traitement théorique des images ellipsométriques est base sur le concept de trajectoires.
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Dal'Bo, Frédéric. "Spectroscopie optique d'heterostructures a base de tellurure de cadmium epitaxiees par jets moleculaires." Grenoble 1, 1988. http://www.theses.fr/1988GRE10123.
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La relaxation des contraintes est mise en evidence par une etude spectroscopique des transitions des excitons libres et varie en fonction de l'epaisseur de la couche et de l'orientation du support. Les differences entre les spectres de photoluminescence des materiaux massifs et ceux des couches epitaxiees sont dues aux effets des contraintes, aux defauts cristallins et aux impuretes introduites pendant la croissance. La structure de bande du puits quantique contraint est etudiee par spectroscopie optique. Elle est etudiee en fonction de l'epaisseur du puits
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Chomette, André. "Proprietes electroniques et optiques des superreseaux gaas/gaalas de petites periodes." Paris 6, 1988. http://www.theses.fr/1988PA066146.
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Wang, Yin-Yu. "Réseaux supraconducteurs : température critique et états mixtes." Grenoble 1, 1987. http://www.theses.fr/1987GRE10060.
Full textAbstract:
Les effets de quantification du flux magnetique sur des reseaux supraconducteurs bidimensionnels sont etudies dans ce memoire. Du point de vue theorique, la temperature de transition supraconductrice en fonction du champ magnetique applique est determinee en resolvant les equations d'alexander pour divers reseaux : periodiques, quasiperiodiques et fractals. Quelques un de ces reseaux submicroniques ont ete realises par lithographie electronique. Leurs temperatures critiques sont mesurees et l'accord entre la theorie et l'experience est discute. A l'interieur de la phase supraconductrice, les vortex entrent dans le reseau et induisent des supercourants diamagnetiques. L'etat d'equilibre est traite d'une maniere analogue au traitement de l'etat mixte d'un supraconducteur massif d'abrikosov : on determine l'amplitude du parametre d'ordre en tenant compte du terme non-lineaire de l'equation de ginzburg-landau par une methode de perturbation. On en deduit les quantites thermodynamiques, en particulier l'energie libre et l'aimantation du reseau, qui sont des fonctions de la difference entre la temperature et la temperature critique t - t::(c), ainsi que du parametre d'abrikosov beta ::(a). Ce formalisme a ete applique au reseau carre pour lequel les configurations du parametre d'ordre et les distributions du courant diamagnetique ont ete determinees pour quelques valeurs simples du champ magnetique. D'autre part, la derivee de la ligne critique par rapport au champ magnetique, qui s'identifie a la derivee du bord du spectre d'hofstadter a ete calculee a l'aide d'une approximation continue. Cette derivee contient un terme anormal que l'on peut relier a la phase de berry. Elle donne directement la derivee de l'aimantation par rapport a la temperature d rond m/d rond t. Nous donnons egalement quelques resultats preliminaires sur l'etat mixte du reseau supraconducteur en presence d'un courant exterieur. Le courant critique au-dessus duquel cet etat n'existe plus est obtenu pour quelques cas simples (boucles, reseau carre). Quelques mesures preliminaires de ce courant ont ete effectuees sur un reseau carre
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Giovanni, Ferioli. "Self-bound quantum droplets in Bose-Bose mixture." Doctoral thesis, 2019. http://hdl.handle.net/2158/1153074.
Full textAbstract:
Self-bound quantum systems appear in different physical scenarios. They result from the
balance between attractive and repulsive forces. Recently the existence of a new object
belonging to this class has been discovered. Using a bosonic mixture of ultracold atoms, it
is possible to generate a self-bound state resulting from the interplay between an attractive
mean-field energy and the repulsive first-order perturbative correction, the so-called Lee-
Huang-Yang term. This system is known as quantum droplet.
During my PhD we have experimentally observed and characterized this novel quantum
state. Thanks to an innovative technique, based on a time-averaged potential, we were able
to levitate the mixture and study for the first time the self-bound nature of quantum droplets
in 3D free space. We characterized their equilibrium properties, i.e. the size, the critical atom
number for their formation and the spin imbalance, finding a very good agreement with the
theoretical predictions.
Despite being extremely dilute, for large atom numbers quantum droplets enter a liquidlike
incompressible regime, highlighted by the formation of a bulk with uniform density.
We investigate the occurrence of this incompressible regime by studying collisions between
two droplets. This is indeed a powerful tool to gain information about the energy scales
characterizing the system. To this aim, we implemented an experimental sequence able to
create two separate quantum droplets and to imprint them a tunable relative velocity.
By characterizing the outcomes of the collisions for different values of velocities and atom
numbers in the droplets and comparing them with the results of energetic considerations and
numerical simulations, we obtained the first evidence of a crossover between compressible
and incompressible regimes.
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CONCLAVE, STEFANO. "A bosonic mixture for the simulation of impurities and quantum magnetism." Doctoral thesis, 2016. http://hdl.handle.net/2158/1042712.
Full textAbstract:
An experimental apparatus for the production of quantum degenerate mixtures of rubidium-87 and potassium-41 was renewed in all of its components (optical setup, vacuum apparatus and part of the control electronics’); the rebuilding process lead to significat improvements
in both the quality of the final atomic samples (number and control on relative balance) and the stability of the system. This was essential in the perspective of its use for the quantum simulation of fundamental problems in physics with ultracold mixtures in optical lattices. The experimental procedure we developed for the production of double Bose-Einstein condensates is described into detail (up to the optical confinement), alongside with an extensive characterization of the current working conditions.