Ce manuscrit décrit des expériences d’optique atomique quantique utilisant un détecteur résolu en impulsions d’atomes uniques d’hélium métastable. La première partie du manuscrit décrit la mesure de cohérence de deuxième ordre de la superradiance à partir d’un condensat de Bose-Einstein d’helium métastable. Bien que le condensat soit cohérent et le gain du processus de superradiance élevé, celle-ci montre toujours une statistique thermique comme celle de l’émission spontanée. La suite du manuscrit est dédiée au test de la non localité d’une source atomique corrélée en impulsion. Le schéma du test s’inspire d’une réalisation faite par Rarity et Tapster sur des photons intriqués en impulsion. Les ingrédients principaux d’un tel schéma sont la source atomique générée par instabilité dynamique du condensat dans un réseau optique en mouvement, le contrôle cohérent des atomes par diffraction de Bragg et la mesure de la corrélation des atomes dans les différentes voies de sortie du schéma interférométrique. Un point clé est le contrôle et la manipulation de la phase des ondes atomiques. Le chapitre 3 décrit les tests sur le contrôle cohérent par diffraction de Bragg et leurs résultats encourageants. La nature non classique de notre source atomique est démontrée par l’observation d’une interférence à deux particules en les envoyant sur une séparatrice atomique. Cet analogue atomique de l’expérience de Hong Ou et Mandel est le sujet du dernier chapitre de ce manuscrit. Le résultat de cette expérience ouvre la possibilité du test d’inégalité de Bell avec des particules massives corrélées sur des degrés de liberté externe. / This manuscript describes quantum atom optics experiments using metastable helium atoms with a single-atom momentum resolved detector. In the first part of this manuscript, the second order correlation measurement of the superradiance from a metastable helium Bose-Einstein condensate is presented. The superradiance effect is the collective radiation of dense ensemble where a strong gain of the radiation is expected. We have shown the thermal like statistics of the emission even in the presence of the strong gain. The next part of the manuscript is devoted to the quantum nonlocality test using a pair of atoms entangled in momentum. The protocol we came up with is inspired from the one of Rarity and Tapster with pairs of photons entangled in momentum. The essential ingredients of this protocol are the atomic pair produced by dynamical instability of the Bose-Einstein condensate in a moving optical lattice, the coherent control of the atomic pair by Bragg diffraction and the correlation measurement of the atoms in different output modes of the interferometric protocol. The experimental characterization and preparation of coherent control by Bragg diffraction are presented showing the proof of principle of such a protocol. The last part of the manuscript discusses the realization of the atomic Hong-Ou-Mandel experiment using the same atomic pair with an atomic beamsplitter. The non-classical interference result of this experiment has opened an opportunity for us to realize Bell’s inequality test with massive particles correlated in external degrees of freedom.

L’émission spontanée de lumière par un émetteur n’est pas un processus intrinsèque. D’une part, il dépend de l’environnement électromagnétique. D’autre part, il dépend de la présence d’autres émetteurs avec lesquels il peut interagir et générer des interférences.Ces deux effets ont été, dans la plupart des cas, étudiés de manière indépendante. L'objectif de cette thèse est d'explorer comment contrôler l'émission de lumière en utilisant simultanément ces deux types d’effets.La première partie est consacrée à une étude théorique d'un système idéal de deux émetteurs couplés à un résonateur. Les deux émetteurs sont placés à proximité, et l’interaction dipôle-dipôle conduit à la formation de deux états, superradiant et sous-radiant. Le système que l’on obtient agit en tant que source et mémoire quantique de photons uniques, efficace et modulable. On étudie ensuite le cas d’un résonateur plasmonique, à symétrie spatiale antisymétrique, qui permet d’exciter efficacement l’état sous-radiant. On montre qu’on obtient ainsi une forte exaltation de l'effet Purcell, tout en conservant un état spectralement étroit.La deuxième partie explore un système comportant un très grand nombre d’émetteurs couplés à un plasmon de surface se propageant le long d’une interface métal air. Les émetteurs sont des nanoplaquettes, ou puits quantiques colloïdaux. Lorsqu’un film de nanoplaquettes est déposé sur le métal, il est possible d’obtenir un couplage fort. Ce couplage au plasmon de surface permet d'obtenir une émission directive et polarisée. / Spontaneous emission of light is not an intrinsic property of an emitter. On the one hand, it depends on the electromagnetic environment. On the other hand, it depends on the presence of other emitters with whom it may interact and generate interferences. Up to date, very few studies address the question of multiple interacting emitters coupled to a resonator. The goal of this thesis is to combine both collective effects and nanoresonators to control the spontaneous emission and scattering of light emitters.First, we theoretically study an ideal system consisting of two emitters coupled to a resonator. The emitters are in close proximity, and the dipole-dipole interaction generates a superradiant state and a subradiant state. The system that we obtain behaves as an efficient, and tunable, single photon source and quantum memory. We then switch to the case of a plasmonic resonator with an antisymmetric mode, which allows to efficiently excite the subradiant state. We show that this results in an enhancement of the Purcell effect while maintaining a spectrally narrow state.In the second part of this thesis, we explore a system of a large number of emitters coupled to a surface plasmon travelling along a metal-air interface.The emitters are nanoplatelets, also called colloidal quantum wells. Strong coupling is obtained when a layer of nanoplatelets is deposited on top of the metal. The coupling of the nanoplatelets to the surface plasmon allows to obtain directional and polarized light emission.

O fenômeno da superradiância é caracterizado por um processo de ordenamento das transições dos dipolos atômicos em amostras excitadas, moderadamente densas, decorrente das correlações induzidas entre os átomos desenvolvidas pela radiação coerente emitida pelos próprios átomos. O processo superradiante que é iniciado a partir de uma total desordem em t = 0 atinge um ordenamento máximo em um tempo τ α N-1, gerando um pulso de radiação de intensidade seguindo a lei do sech2 e com pico proporcional à N2, e em seguida os dipolos relaxam para um equilíbrio desordenado. Neste trabalho, tratamos a interação de dois modos de uma cavidade, ωa e ωb, e uma amplificação, com um sistema de N átomos de dois níveis, com frequência de transição atômica ω0 de forma que interaja ressonantemente com ωa e dispersivamente com ωb, responsável pelo acoplamento entre os átomos. Para enterdemos como a lei do sech2 será afetada pela interação direta entre os átomos, utilizamos o método das perturbações via de pequenas rotações não-lineares para obtermos o hamiltoniano efetivo do sistema com uma forma mais explícita da interação dipolar entre os átomos. Por fim, após escrevermos a equação mestra do sistema, utilizamos a aproximação de campo médio e o método dos invariantes de Lewis-Riesenfeld para chegar aos principais aspectos deste fenômeno no sistema. / The superradiant phenomena is characterized by atomic dipoles ordering process in excited samples moderately denses, that occours due to the atomic induced correlations developed not directly but by the coherent radiation emitted by atoms themselves. The superradiant process evolves from a total disorder at t = 0, attain a maximum order in a time τ α N-1 creating a radiation pulse whose intensity follows the sech2 law and its peak is proportional to N2, thereafter the dipoles relax to a disordered equilibrium state. In this essay, we deal with the interaction between two cavity modes ωa and ωb and a classical pump with a system of N two-level atoms, whose atomic transition frequencies ω0. We consider a resonant interaction between atoms and mode ωa and a dispersive coupling of atoms with mode ωb, which couple the atomic sample, and the classical pump. In order to obtain how sech2 law changes, we use the method of nonlinear small rotations to obtain effective Hamiltonian, expliciting dipolar interaction between atoms. Finally, after write the effective master equation, we use the mean-field approximation and Lewis and Riesenfeld method to obtain the mean features of this phenomena to our system.

In this thesis we study a test electromagnetic field in the vicinity of Kerr black hole and with methods of extraction of its rotational energy. We are investigating a process in which a particle moves in an electromagnetic resonator around Kerr black hole. The energy of the particle is transferred to the electromagnetic field and the particle falls into the black hole with negative energy. We begin with the derivation of Maxwell's and Teukolsky equations and their numerical solutions. We derive a boundary condition for an electromagnetic field on a spherical mirror around the black hole, find the field that satisfies this condition, and describe the procedure for numerical calculation. Next, we calculate the trajectories of charged test particles in such a field and find particles that fall into the black hole with negative energy. We have found that it is possible for the particle to fall into the black hole with the energy of −124% of its rest mass, and the parameters of the electromagnetic field and trajectory of the particle need to be carefully selected.

En Electrodynamique Quantique en Cavité (" Cavity QED "), l'interaction entre la transition atomique et le champ de la cavité est quantifiée par la fréquence de Rabi du vide. L'expression analogue " circuit QED " a été introduite pour certains circuits supraconducteurs contenant des Jonctions Josephson, parce qu'ils pouvaient se comporter comme des atomes artificiels couplés au mode bosonique du résonateur. Dans le régime où la fréquence de Rabi du vide est comparable à la fréquence de transition du système à deux niveaux, des transitions de phases quantiques superradiantes ont été prédites pour le fondamental du système, par exemple dans le cadre du modèle de Dicke. Des réalisations possibles du modèle de Dicke par des systèmes de circuit QED sont étudiées ici théoriquement dans les cas de couplage capacitif ou inductif. Prédictions et contraintes sont analysées pour l'obtention d'une transition de phase quantique, avec un vide deux fois dégénéré au-dessus d'un point critique quantique. La robustesse et la protection de la dégénérescence du vide dans le régime de couplage ultrafort sont étudiées, et conduisent à de possibles applications en Information Quantique avec des réseaux de plusieurs résonateurs. Finalement, un modèle de Dicke généralisé avec une phase doublement superradiante et un vide quatre fois dégénéré est proposé.

O fenômeno da superradiância é caracterizado por um processo de ordenamento das transições dos dipolos atômicos em amostras excitadas, moderadamente densas, decorrente das correlações induzidas entre os átomos desenvolvidas pela radiação coerente emitida pelos próprios átomos. O processo superradiante que é iniciado a partir de uma total desordem em t = 0 atinge um ordenamento máximo em um tempo τ α N-1, gerando um pulso de radiação de intensidade seguindo a lei do sech2 e com pico proporcional à N2, e em seguida os dipolos relaxam para um equilíbrio desordenado. Neste trabalho, tratamos a interação de dois modos de uma cavidade, ωa e ωb, e uma amplificação, com um sistema de N átomos de dois níveis, com frequência de transição atômica ω0 de forma que interaja ressonantemente com ωa e dispersivamente com ωb, responsável pelo acoplamento entre os átomos. Para enterdemos como a lei do sech2 será afetada pela interação direta entre os átomos, utilizamos o método das perturbações via de pequenas rotações não-lineares para obtermos o hamiltoniano efetivo do sistema com uma forma mais explícita da interação dipolar entre os átomos. Por fim, após escrevermos a equação mestra do sistema, utilizamos a aproximação de campo médio e o método dos invariantes de Lewis-Riesenfeld para chegar aos principais aspectos deste fenômeno no sistema. / The superradiant phenomena is characterized by atomic dipoles ordering process in excited samples moderately denses, that occours due to the atomic induced correlations developed not directly but by the coherent radiation emitted by atoms themselves. The superradiant process evolves from a total disorder at t = 0, attain a maximum order in a time τ α N-1 creating a radiation pulse whose intensity follows the sech2 law and its peak is proportional to N2, thereafter the dipoles relax to a disordered equilibrium state. In this essay, we deal with the interaction between two cavity modes ωa and ωb and a classical pump with a system of N two-level atoms, whose atomic transition frequencies ω0. We consider a resonant interaction between atoms and mode ωa and a dispersive coupling of atoms with mode ωb, which couple the atomic sample, and the classical pump. In order to obtain how sech2 law changes, we use the method of nonlinear small rotations to obtain effective Hamiltonian, expliciting dipolar interaction between atoms. Finally, after write the effective master equation, we use the mean-field approximation and Lewis and Riesenfeld method to obtain the mean features of this phenomena to our system.

Orientadores: Alberto Vazquez Saa, Amir Ordacgi Caldeira / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-17T18:21:33Z (GMT). No. of bitstreams: 1 Richartz_Mauricio_D.pdf: 3399746 bytes, checksum: 3da68926653d0bbb338f76240696b246 (MD5) Previous issue date: 2011 / Resumo: A Conjectura da Censura Cosmica, proposta por Roger Penrose em 1969, afirma que singularidades resultantes de um colapso gravitacional estão sempre envolvidas pelo horizonte de eventos de um buraco negro. O objetivo desse trabalho é investigar processos de tunelamento quântico que visam violar essa conjectura. Através do formalismo de Newman-Penrose, é feita, inicialmente, uma análise de perturbações escalares, de neutrinos, eletromagneticas e gravitacionais nas métricas de Kerr e de Reissner-Nordstr om. Processos de espalhamento ondulatorio nessas métricas são estudados e coeficientes de transmissão e reflexão para ondas incidentes são calculados nos limites de baixas energias. A partir desses resultados, experimentos imaginários com o intuito de destruir o horizonte de eventos de um buraco negro e expor sua singularidade para um observador externo são propostos e analisados. A superradiância, fenômeno no qual ondas incidentes são amplificadas ao serem refletidas por um potencial espalhador, se manifesta nesses experimentos e, por isso, é tratada com detalhes e de uma forma bastante geral nesse trabalho. Por fim, experimentos que visam detectar a radiação Hawking e o fenômeno da superradiância em modelos análogos de gravitação são analisados. Em particular, um experimento proposto por mim, em colaboração com Silke Weinfurtner, cujo objetivo e investigar a possibilidade de obtenção de superradiância em laboratório, é discutido / Abstract: The Cosmic Censorship Conjecture, proposed by Roger Penrose in 1969, asserts that singularities arising from the gravitational collapse of a body are always encompassed by the event horizon of a black hole. The main purpose of this work is to investigate quantum tunneling processes whose objetive is to violate this conjecture. Using the Newman-Penrose formalism, scalar, neutrino, electromagnetic and gravitational perturbations in both Kerr and Reissner-Nordstr om metrics are analysed. Wave scattering processes in these metrics are studied and transmission and reflection coecients for incident waves are calculated in the limit of small energies. From these results, gedanken experiments with the purpose of destroying the event horizon of a black hole and exposing its inner singularity to an external observer are proposed and analysed. Superradiance, phenomenum in which incident waves are amplified when reflected by a scattering potential, manifests itself in these thought experiments and, therefore, is also treated in detail in this work. Finally, some experiments with the purpose of detecting Hawking radiation and superradiance in analogue models of gravity are analysed. In particular, an experiment proposed by me, in collaboration with Silke Weinfurtner, whose aim is to investigate the possibility of superradiance detection in laboratory, is discussed / Doutorado / Física das Particulas Elementares e Campos / Doutor em Ciências

This thesis covers three different topics. The first part is a pedagogical review of the basic principles and recent advances in nonlinear optics. It was originally written as a chapter for the proceedings of the “International School of Physics (Enrico Fermi)” summer school on Photonics held in June, 2014. It is included to provide some background information about nonlinear optical processes in general, and is particularly relevant for the third part of this thesis which is based on the second-order nonlinear optical process of spontaneous parametric downconversion. The second part is based on original research, and deals with superradiance in plasmonic nanostructures. The process of superradiance, as introduced by Dicke in 1954, entails the shortening of the spontaneous emission lifetime of a collection of N quantum emitters as a consequence of the development of a macroscopic dipole moment. Specifically, the lifetime is shortened by a factor of 1/N, and the linewidth is broadened by a factor of N. Such a linewidth dependence has been previously observed in systems of several plasmonic ‘emitters’. However, a clear physical insight into this phenomenon and how it relates to Dicke superradiance has not been shown yet. In this part, we demonstrate by experiment, simulation, and a simple analytical model that Dicke’s superradiance can indeed be observed in a planar array of plasmonic nanoantennas, with a linewidth that scales linearly with the number of nanoantennas within a square wavelength. The third part is also based on original research, and is based on the scal- ing laws of spontaneous parametric downconversion (SPDC) for a type-I phase- matching configuration. The variation of bi-photon generation rate, heralding efficiency and radiance with parameters such as crystal length, pump focussing and collection waist sizes are examined for collinear and non-collinear emission. The results can be used to maximize the brightness of the SPDC source or increase the heralding efficiency depending on the application.

Superradiance is an enhanced decay of an excited system of emitters resulting from their mutual coupling. This thesis is focused on superradiance of the emitters coupled via their interaction with a plasmonic nanoparticle. So-called plasmon-mediated superradiance results in even stronger enhancement of the decay rate as the nanoparticle serves as an additional decay chanel. We have developed a quantum model of the system of emitters coupled to a plasmonic nanoparticle, which allows us to differentiate between a pure dephasing and decay processes. We show that the pure dephasing can destroy the cooperative effect leading to superradiance. Furthermore, we have studied how the direct mutual coupling between emitters affects time evolution of the system in dependence on its configuration, and we show conditions when a decay of the system is dramatically decreased by direct coupling.

String theory is currently the best-known candidate for a theory of quantum gravity, having the necessary ingredients to describe all known elementary particles and interactions. It also includes several novel features, arising, for instance, from the additional six compact dimensions required for its internal consistency, making it the natural arena to construct extensions of the Standard Model. In this thesis, we analyze some of the new phenomenological aspects introduced by string theory within the framework of low energy effective theories, focusing on their applications to cosmology, astrophysics and collider experiments. We first consider a particular realization of the brane-world scenario in branonium bound states, showing that the orbital motion of a probe antibrane about a central brane stack leads to a resonant amplification of its world-volume scalar modes. We analyze the cosmological development of this process and also its potential relevance for either dark or baryonic matter generation in the early universe. We then focus on the spectrum of quark and lepton string excitations in warped compactifications, modeled by an effective 5-dimensional Randall- Sundrum throat. Motivated by the observed fermion mass hierarchy, we show that the spin-3/2 Regge excitation of the right-handed top quark is the lightest of such resonances in a significant region of parameter space, possibly lying below the TeV scale, and discuss its potential signatures at the Tevatron and at the LHC. Finally, we study the emission of sub-eV scalar particles by maximally rotating Kerr black holes, motivated by the recent string axiverse proposal. We focus on the spectrum of unstable scalar bound states in the superradiant regime, leading to an exponentially large axion cloud around astrophysical black holes, and analyze two semi-analytical methods for computing the growth rate of this instability, comparing the obtained results with previous analytical and numerical analyses.