Le but de cette thèse a été de mettre en évidence notre capacité à utiliser des boîtes quantiques semi-conductrices comme support à la réalisation de bits quantiques, briques élémentaires de l'information quantique. Nous avons ainsi démontré la possibilité de définir un système à deux niveaux, dont l'initialisation et le contrôle est réalisable au moyen d'impulsions lumineuses picosecondes et déterminé le temps durant lequel nous étions en mesure de conserver sa cohérence. Les oscillations de Rabi entre niveau fondamental et niveau excité permettent d'initialiser le système dans une superposition cohérente pouvant être ensuite manipulée par une deuxième impulsion au cours d'expériences de contrôle cohérent. Le temps de cohérence T2 du système n'est pas seulement limité par la durée de vie radiative T1 et reste très inférieur à la valeur théorique T2= 2T1. Les différents mécanismes de décohérence entrant en jeu ont dès lors été étudiés, en particulier le rôle des phonons acoustiques, responsables d'un fort amortissement des oscillations de Rabi et d'une diminution du temps de cohérence pour une partie des boîtes quantiques étudiées. Nous avons cependant dans certains cas mis en évidence la présence de mécanismes supplémentaires, liés aux fluctuations de l'environnement électrostatique des boîtes. Par ailleurs, une étude poussée de la polarisation de la luminescence émise par ces boîtes, dont la croissance a été réalisée en régime Stranski-Krastanov, a révélé une inclinaison des états propres de la structure fine de l'exciton, ainsi qu'une modification de leur intensité d'émission, témoignant d'un fort mélange des états lourds et légers de la bande de valence

Heinrich Heine (1797-1856) é costumeiramente lembrado como um escritor engajado. Ora lido como um defensor do povo judeu do qual descendia ora como um intelectual livre que buscou um olhar crítico sobre as religiões e sobre o mundo burguês em formação. Sua obra O Rabi de Bacherach (1840) literaliza a saga do povo judeu em face do cristianismo na Alemanha. Eis, portanto, um vasto leque de possibilidades para análise do engajamento político de Heine, que se mostra nessa obra não de modo panfletário, senão a partir de uma visão crítica da religião. Dentro desse viés, o presente trabalho propõe-se a fazer uma leitura do seu Rabi destacando os recursos estilísticos da ironia e da paródia, acionadas frequentemente por Heine para operar com forças políticas de sua época, o que marcou profundamente sua poética ao mesmo tempo jocosa e crítica. / Heinrich Heine (1797-1856) is usually remembered as a politically engaged writer. Sometimes he is thought of as a defender of the Jewish people from whom he descended sometimes like a free thinker, who had a critical point of view about religions and the emerging bourgeoisie world. His work The Rabbi of Bacherach (1840) describes the saga of the Jewish people in view of Christianity in Germany. Thus, there is a wide range of possibilities to analyze Heines political engagement, which appears in this work not like pamphlet literature, but from a critical point of view about religion. In this context, the present work intends to point out the stylistical mechanisms of irony and parody in his Rabbi, which were often used by Heine to work with political forces of his time. Consequently his poetry was marked both in a funny and in a critical way.

This paper focuses on some areas related to the topic of the Ten Commandments. Main part is a translation of chosen chapters of the work Tiferet Yisrael. Namely Chapters 33-36, which describes the opinion of the author (Rabbi Loew) on this topic. The translation is accompanied by commentary, which make it more comprehensive, and it is compared with texts that are in the environment of traditional Judaism deemed as essential. Powered by TCPDF (www.tcpdf.org)

Les développements en information quantique nécessitent le contrôle et la manipulation d'états quantiques. Parmi les systèmes en physique du solide, les boîtes quantiques semiconductrices sont de bons candidats pour réaliser des bits quantiques. La taille nanométrique de ces objets conduit à un confinement spatial à trois dimensions des porteurs : le spectre d'énergie est discret comme celui d'un atome. Ces objets sont étudiés pour leurs propriétés optiques, et notamment pour l'émission de photons uniques et indiscernables, qui sont des états quantiques de la lumière. Le travail de cette thèse consiste à étudier des boîtes quantiques uniques d'InAs/GaAs excitées à la résonance de leur transition optique, à l'aide d'impulsions lumineuses picosecondes. Grâce à une géométrie unidimensionnelle en guide d'onde, il est possible de s'affranchir de la lumière diffusée du laser d'excitation, et d'observer la luminescence résonante des boîtes. On atteint alors le régime d'oscillations de Rabi qui permet d'inscrire dans la boîte une superposition cohérente du système à deux niveaux, c'est un bit quantique. Cependant, le couplage entre la boîte et son environnement modifie les propriétés de cohérence des boîtes quantiques, limitant la possibilité de réaliser des opérations sur les qubits. Deux phénomènes principaux de décohérence ont été modélisés : l'interaction avec les phonons longitudinaux acoustiques de la matrice environnante de la boîte et le couplage avec le mode électromagnétique. Nous avons enfin étudié la statistique d'émission de photons des boîtes quantiques, et nous montrons qu'elles constituent de bonnes sources de photons uniques indiscernables, à la demande. / Developments in quantum information require controlling and manipulating quantum bits. Among solid state emitters, semiconductor quantum dots seem promising to realize quantum bits. First, the nanometric size of those structures leads to the confinement of the carriers in the three directions of space, so that their energy spectrum becomes atom-like. Furthermore, they can easily be integrated into electronic and optic devices. Such structures are studied for their optical properties, especially the emission of single and indistinguishable photons, which are quantum states of light. In the present work InAs/GaAs quantum dots have been studied under resonant excitation with picosecond laser pulses. One-dimensional waveguiding geometry has been used to suppress the scattered excitation laser allowing the observation of a single dot resonant luminescence. The coupling between the laser and the dot leads to the Rabi oscillations regime which enables to address a coherent superposition of states in the two-level system, meaning a quantum bit. However, the coupling between the dot and its environment changes the coherence properties of the dots, limiting the time during which operations on the qubits are possible. Two main phenomena have been observed and studied: the interaction between the dots and the longitudinal acoustic phonons of the GaAs matrix and the coupling with the electromagnetic mode. Finally, the photon emission statistics of the quantum dots have been studied, showing that quantum dots are on demand good emitters of indistinguishable single photons.

No description available.

Abstract An optical lattice is a periodic array produced by the superposition of two or more counter-propagating laser beams which interfere and create a spatial periodic intensity pattern. An important difference between a solid state crystalline lattice and an optically induced lattice is that the latter have a longer coherence time which permits the observation of coherent phenomenon such as Bloch oscillations. Recently, an interesting effect has been reported in the literature, which is the analogue of Rabi oscillations in two level systems driven by an external optical field: an optical beam composed by pair of frequencies, resonants with the high symmetry points of the Brillouin zone, propagating through an optical lattice exhibits oscillations of the Fourier ways between the frequencies due to the coupling with the lattice. Therefore, in the optical case the field plays the role of the matter, while the lattice plays the role of the driving field which couples the frequencies. Based in this result, the objective of this paper is to investigate the influence of self-defocusing in the optical Rabi oscillation. We have shown, through numerical calculation of the wave nonlinear equation, that in the self-defocusing optical lattice, these oscillations go disappearingare. The result of the disappearance of the oscillations of Fourier can be understood considering that self-defocusing promotes an addition of phases in the ways that were resonant - kB and kB, in different way, form that the basic difference between kB and - kB will not be plus a vector of the reciprocal net, and as consequence the oscillations of optic Rabi disappear, therefore the coupling with the net requires this condition in the resonant frequencies. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Resumo Uma rede opticamente induzida é um arranjo periódico produzido pela superposição de dois ou mais feixes de laser que ao interferirem criam um padrão de intensidade periódico espacial. Uma importante diferença entre uma rede cristalina no estado sólido e uma rede produzida opticamente é que a última apresenta um tempo de coerência longo, permitindo a observação de fenômenos coerentes tal como as oscilações de Bloch. Recentemente, um efeito interessante análogo às oscilações de Rabi em um sistema atômico de dois níveis impulsionado por um campo externo, foi publicado na literatura: um feixe óptico composto de um par de freqüências, ressonantes com os pontos de alta simetria da zona de Brillouin, propagando - se através de uma rede óptica exibe oscilações dos modos de Fourier entre as freqüências adequadas para o acoplamento com a rede. Portanto, no caso óptico o campo representa a matéria, enquanto a rede representa a intensidade do campo aplicado que acopla as freqüências. Baseado neste resultado, o objetivo desta dissertação é investigar a influência da auto - desfocalização nas oscilações ópticas de Rabi. Demonstraremos, através de cálculos numéricos da equação de onda não linear, que em uma rede opticamente induzida na presença da auto - desfocalização, essas oscilações vão desaparecendo. O resultado do desaparecimento das oscilações de Fourier pode ser compreendidoconsiderando que a auto - desfocalização promove um adicionamento de fases nos modos que eram ressonantes -kB e kB, de maneira diferente, de forma que a diferença básica entre kB e -kB não será mais um vetor da rede recíproca, e como conseqüência as oscilações de Rabi óptica desaparecem, pois o acoplamento com a rede requer esta condição nas freqüências ressonantes.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais / The recent progress in the manufacturing of semiconductor quantum dots (QD) systems has made possible the coherent control of quantum states in QDs using optical or electrical techniques. Laser pulses have been recently used to coherently coponto quânticontrol the exciton population in QDs. The coherent manipulation of quantum states is a high priority task to the development of quantum information and quantum computation. One particular signature of coherency in quantum systems is the Rabi oscillations, which were recently observed in a few experimental works. Here we theoretically study a system composed of a semiconductor QD, tunnel coupled to electron reservoirs. In the presence of a laser field an electron-hole pair is created in the QD. An external source-drain (bias) voltage allows electrons and holes to tunnel to the reservoirs. The study was developed via the non-equilibrium Green s function technique. We solve numerically a set of coupled differential equations to the retarded and lesser Green functions. This gives the occupation probabilities of the two levels of the QD and the laserinduced photocurrent as a function of time. We focus our attention on the effects of temperature on the Rabi oscillations. Our main findings encompass a thermal activated Pauli blockade of the Rabi oscillations that can be controlled via the reservoirs temperature. We also discussed the effects of this thermal activation of Pauli blockade on the photocurrent. These results suggest that ability to measure temperatures via quantum coherent signals, thus suggesting the possibility of a new quantum-dot based thermometer. / O recente progresso na fabricação de sistemas de pontos quânticos semicondutores (PQ) tem tornado possível o controle coerente de estados quânticos em PQs utilizando técnicas ópticas ou elétricas. Pulsos de laser têm sido recentemente utilizados para controlar coerentemente a população de éxcitons em PQs. A manipulação coerente de estados quânticos é uma tarefa de alta prioridade para o desenvolvimento da informação e computação quântica. Uma assinatura particular de coerência em estados quânticos são as oscilações de Rabi, as quais foram recentemente observadas em trabalhos experimentais. Neste trabalho estudamos, teoricamente, um sistema composto por um PQ semicondutor, túnel-acoplado a reservatórios de elétrons. Na presença de um campo de laser um par elétron-buraco é criado no PQ. Uma tensão fonte-dreno (bias) permite que elétrons e buracos tunelem para os reservatórios. O estudo foi desenvolvido através da técnica de funções de Green de não-equilíbrio. Resolvemos numericamente um conjunto de equações diferenciais acopladas para as funções de Green retardada e menor. Estas fornecem a probabilidade de ocupação dos dois níveis no PQ e a fotocorrente induzida por laser. Concentramos nossa atenção nos efeitos da temperatura sobre as oscilações de Rabi. Nossos principais resultados incluem um bloqueio de Pauli termicamente ativado na fotocorrente. Estes resultados sugerem a habilidade de medir temperatura via sinais quânticos coerentes, sugerindo, assim, a possibilidade de um novo termômetro baseado em pontos quânticos. / Mestre em Física

No description available.

<p>This thesis is based on a selection of six different experimental techniques used for studies in atomic and molecular physics. The techniques analysed in the thesis are compared to find similarities in strategies and ways to avoid sources of error.</p><p>Paper 1 deals with collision based spectroscopy with 60 keV Xe6+ ions on sodium and argon gas targets. Information on energy of Rydberg states in Xe5+ is unveiled by optical spectroscopy in the wavelength range from vacuum ultraviolet (VUV) to visible. In paper 2, the fast ion-beam laser spectroscopy (FIBLAS) is adapted for measuring hyperfine structure of barium isotopes in an isotopically pure ion-beam. This techniques involves changing the isotope during the measurement to minimize sources of error in measurement and enhance the signal from lesser abundant isotopes. The FIBLAS technique is used in paper 3 to study samarium ions. The ions are optically pumped and the recorded optical nutation is used to measure transition probabilities. This technique eludes the difficulties inherent in relative intensity measurements of all the radiative transitions from an excited state. In Paper 4, optical emission spectroscopy is used in the VUV region to study noble gas mixture discharges. The source of the emission bands near the resonance lines of krypton and xenon are found to be heteronuclear dimers. In paper 5, radiation from a pulsed argon plasma with admixture of nitrogen is studied with time resolved spectroscopy in the VUV and ultraviolet wavelength ranges to investigate the mechanism of energy transport. A metastable state of atomic argon is found to be an important source of energy to many radiative processes. In Paper 6, photoelectron spectroscopy (PES) on thiophene, on 3-bromothiophene and on 3,4-dibromothiophene using time-of-flight photoelectron-photoelectron coincidence technique and conventional PES to investigate the onset of double ionisation compared to the onset of single ionisation in molecules.</p>

Un atome de Rydberg circulaire et un champ électromagnétique stocké dans une cavité supraconductrice de très grand facteur de qualité constituent un système simple, bien isolé de son environnement et permettant d'étudier l'interaction rayonnement-matiére. Dans ce mémoire nous présentons une expérience réalisé dans une situation où l'atome et le champ sont en résonance. Le signal de Rabi correspondant à l'évolution de la population atomique présente des composantes de Fourier dont les fréquences sont proportionnelles aux racines carrées des entiers successifs ; ceci met directement en évidence la quantification du champ dans la cavité. Nous montrons également que l'analyse des signaux permet de remonter aux propriétés statistiques du champ. Enfin, en analysant l'interaction non résonante de l'atome avec la cavité, nous montrons que dans un futur proche, il sera possible de préparer des superpositions quantiques d'états du champ présentant des différences mésoscopiques. Ces états sont de type "chat de Schrödinger". L'étude de la décohérence de ces états en fonction du nombre de photons que contient le champ permet d'explorer la frontière qui existe entre le monde quantique et le monde classique.