A compressão nas flutuações da diferença de intensidades dos feixes sinal e complementar gerados por um OPO acima do limiar foi medida já há algum tempo e constituiu um dos principais interesses nestes sistemas. Emaranhamento entre esses feixes, entretanto, ainda não foi experimentalmente demonstrado em circunstâncias normais de operação acima do limiar (feixes não-degenerados em frequência). Usando um critério de não-separabilidade entre sistemas contínuos, buscamos verificar se a variância de um par de operadores tipo EPR, a diferençaa de intensidades e a soma das fases de sinal e complementar, pode violar uma desigualdade suficiente para caracterizar emaranhamento. Após um estudo teórico, verificamos que isto pode de fato ocorrer numa região de parâmetros experimentalmente acessível. A medida não foi realizada até hoje devido à dificuldade em se medir quadratura fase, o que, neste caso, exigiria o uso de osciladores locais em frequências distintas. Motivados por isso, propomos uma montagem experimental que utiliza cavidades óticas para projetar ruído de fase em ruído de intensidade, tornando dessa forma acessível a medida de anticorrelação de fase entre sinal e complementar. Realizamos nossa proposta em caráter preliminar, obtendo resultados encorajadores, embora não conclusivos, que indicam a existência de emaranhamento. / Squeezing in the intensity difference of signal and idler beams generated by an OPO operating above threshold was observed some time ago and presented one of the major attraction of this system. Entanglement between the macroscopic fields, however, has not yet been demonstrated in normal operation conditions above threshold (non-degenerate beams). Using a non-separability criterion for continuous variables, we investigate whether the variances of a pair of EPR-like operators, difference of intensities and sum of phases of signal and idler, can violate a Bell-type inequality and hence characterize entanglement. After a theoretical study, we verified that entanglement can occur in an experimentally accessible region of parameters. This measurement was not performed to date owing to the difficulty of measuring the phase quadratures, which usually requires the use of local oscillators with slightly different frequencies. Motivated by this, we propose an experimental setup that uses optical cavities to rotate the noise ellipse of each beam, projecting phase noise into intensity noise, thus allowing the experimental access to the phase quadratures. We preliminarly implemented our proposal and obtained promising although not conclusive results, that indicate entanglement.

Orientador: José Antonio Roversi / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-20T23:06:34Z (GMT). No. of bitstreams: 1 Roque_ThalesFigueiredo_M.pdf: 4513526 bytes, checksum: 591f56a02e8cf1895d520faa78c27465 (MD5) Previous issue date: 2012 / Resumo: Neste trabalho analisamos a dinâmica das correlações quânticas em um sistema composto por dois osciladores harmônicos em contato com um mesmo reservatório térmico e acoplados entre si com um acoplamento dependente do tempo. O reservatório térmico modelado de acordo com o modelo de Caldeira-Leggett e tanto a abordagem via integrais de caminho quanto a abordagem via equações mestras são usadas para estudar o sistema nos regimes Markoviano e não-Markoviano. O Hamiltoniano que descreve o sistema é bilinear nos operadores de campo, isto significa que se repararmos o sistema em um estado Gaussiano, o estado do sistema sera sempre Gaussiano. Para um estado Gaussiano toda a informa ¸ao sobre as correlações quânticas está contida na matriz de covariância s. Conhecida a matriz s podemos medir o emaranhamento usando a negatividade Logarítmica e calcular uma aproximação para a discórdia quântica em estados Gaussianos, que é a discórdia Gaussiana. Nós mostramos que mesmo à temperaturas muito altas as correlações quânticas, inclusive o emaranhamento, persistem. Esta persistência tem uma relação estreita com a estabilidade do sistema. Como as correlações quânticas são a principal assinatura da mecânica quântica, isto sugere que este tipo particular de acoplamento entre os osciladores pode reduzir a descoerência, introduzida pela interação com o reservatório térmico / Abstract: In this work we analise the dinamics of quantum correlations in a system composed by two harmonic oscillators in contact with a common heat bath and coupled with each other by a time dependent coupling. The heat bath is modeled according to the Caldeira-Leggett model and both the path integral and the master equation approaches are used to study the system in the Markovian and in the non-Markovian regime. The Hamiltonian that describes the system is bilinear in the field opperators, this means that if we prepare the system in a Gaussian state, it remains in a Gaussian state indefinitely. For a Gaussian state all the information about the quantum correlations is in the covariance matrix s and we are able to calculate the Logarithmic Negativity as a measure of the systems¿ entanglement and the Gaussian discord as an approximantion to the usual quantum discord, that is a measure of quantum correlations. We have shown that in some circunstances we can observe the survival of quantum correlations and entanglement, even at very high temperatures. This survival has close relationship with the stability of the system¿s equation of motion. As quantum correlations are the main feature of quantum mechanics, this sugests that this particular coupling between the oscillators can reduce the decoherence effects induced by the interaction with the heat bath / Mestrado / Física / Mestre em Física

This dissertation is ordered into three Parts. Part I is an investigation into identity, indiscernibility and individuality in logic and metaphysics. In Chapter 2, I investigate identity and discernibility in classical first-order logic. My aim will will be to define four different ways in which objects can be discerned from one another, and to relate these definitions: (i) to the idea of symmetry; and (ii) to the idea of individuality. In Chapter 3, the four kinds of discernibility are put to use in defining four rival metaphysical theses about indiscernibility and individuality. Part II sets up a philosophical framework for the work of Part III. In Chapter 4, I give an account of the rational reconstruction of concepts, inspired chiefly by Carnap and Haslanger. I also offer an account of the interpretation of physical theories. In Chapter 5, I turn to the specific problem of finding candidate concepts of particle. I present five desiderata that any putative explication ought to satisfy, in order that the proposed concept is a concept of particle at all. Part III surveys three rival proposals for the concept of particle in quantum mechanics. In Chapter 6, I define factorism and distinguish it from haecceitism. I then propose an amendment to recent work by Saunders, Muller and Seevinck, which seeks to show that factorist particles are all at least weakly discernible. I then present reasons for rejecting factorism. In Chapter 7, I investigate and build on recent heterodox proposals by Ghirardi, Marinatto and Weber about the most natural concept of entanglement, and by Zanardi about the idea of a natural decomposition of an assembly. In Chapter 8, I appraise the first of my two heterodox proposals for the concept of particle, varietism. I define varietism, and then compare its performance against the desiderata laid out in Chapter 5. I argue that, despite its many merits, varietism suffers a fatal ambiguity problem. In Chapter 9, I present the second heterodox proposal: emergentism. I argue that emergentism provides the best concept of particle, but that it is does so imperfectly; so there may be no concept of particle to be had in quantum mechanics. If emergentism is true, then particles are (higher-order) properties of the assembly, itself treated as the basic bearer of properties.

Orientador: Amir Ordacgi Caldeira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-14T14:38:31Z (GMT). No. of bitstreams: 1 Valente_DanielMendonca_M.pdf: 3285803 bytes, checksum: ada969db5abe126088faf5bdf5aa0c24 (MD5) Previous issue date: 2009 / Resumo: Este trabalho consiste em um estudo do emaranhamento em sistemas quânticos abertos, modelados como partículas brownianas. O interesse surge da possibilidade de entender como o meio pode criar ou manter emaranhamento entre sistemas quânticos, em vez de somente ocasionar perda de coerência e energia. Primeiramente, revisamos os significados do emaranhamento em mecânica quântica e algumas formas de quantificá-lo. Em seguida, estudamos a literatura de sistemas quânticos abertos para uma partícula, em especial o movimento browniano quântico. Com isso, foi possível calcular o emaranhamento entre uma partícula quântica browniana e seu reservatório. Numa segunda etapa, estudamos o modelo de duas partículas brownianas em um banho comum. Esse modelo permite a introdução não só de uma escala de tempo característica como também uma de comprimento. Um potencial efetivo entre as partículas surge no modelo como consequência das hipóteses assumidas. Na ausência de potencial externo, é preservada a invariância translacional do sistema. Porém, pudemos alcançar nosso principal resultado, que foi calcular a matriz densidade das duas partículas em equilíbrio térmico e, com ela, o emaranhamento entre as partículas / Abstract: This work consists in a study of entanglement in open quantum systems, within the brownian particles model. The interest comes from the possibility of understanding the mechanisms that lead the environment to create or to keep entanglement between quantum systems and not only make them lose energy or coherence. We start by making a review of the meaning of entanglement to quantum mechanics and some ways to quantify it. Then, we study the literature of open quantum systems for one particle, specially the quantum brownian motion. Moreover, it has been possible to calculate the entanglement between the quantum brownian particle and its reservoir. At a second stage, we studied the model of two brownian particles in a common bath. This model permits not only the introduction of a time scale but also of a lenth one. An effective potential between the particles emerges in the model as a consequence of our assumptions. In the absence of an external potential, the system's translational invariance is preserved. The last step was to achieve what became our main result. We have calculated the equilibrium density matrix for the two brownian particles and the entanglement between them / Mestrado / Física Geral / Mestre em Física

Dans cette thèse, nous étudions d'un point de vue théorique différents aspects de la matière topologique. Ces systèmes présentent des propriétés résistantes aux éventuelles perturbations grâce à une topologie non-triviale de leur structure de bandes. En particulier, des excitations exotiques, par exemple des fermions de Majorana, peuvent apparaitre à leurs bords.L'entropie d'intrication, ainsi que le spectre d'intrication ont été fondamentaux dans l'étude théorique de ces systèmes, et plus généralement des phases libres. Il est cependant difficile de les mesurer expérimentalement. L'étude des fluctuations de charge bipartites a été proposée afin de remédier à ce problème, et celles-ci permettent une mesure faible de l'intrication, en particulier pour des modèles unidimensionnels libres. Nous généralisons les précédents travaux sur les Liquides de Luttinger à des familles génériques de supraconducteurs et isolants topologiques en une et deux dimensions, systèmes dans lesquels la charge observée n'est plus conservée. Nous montrons que les transitions de phases topologiques sont caractérisées par certains coefficients universels dans les fluctuations et les fonctions de corrélations. Les systèmes bidimensionnels que nous étudions présentent des cônes de Dirac, et ces coefficients dépendent de leur enroulement. Cela nous permet de caractériser la topologie de ces points critiques. Dans tous les cas, les fluctuations suivent une loi de volume, qui a un comportement non-analytique aux transition de phase.Dans un second temps, nous nous intéressons aux systèmes en interactions. Nous montrons tout d'abord que certaines des signatures des transitions topologiques survivent en leur présence, dans les supraconducteurs topologiques. Nous étudions ensuite le diagramme de phase de deux fils supraconducteurs couplés par une interaction Coulombienne. Celle-ci mène à la création de phases exotiques grâce à la compétition avec la supraconductivité non-conventionnelle. Nous montrons en particulier l'apparition de phases de Mott brisant spontanément la symétrie de renversement du temps et présentant des courant orbitaux non-triviaux, ainsi que celle d'une phase de fermions libres, qui est l'extension de deux chaînes de Majorana critiques en interaction.Enfin, nous nous intéressons aux effets de la présence de fermions de Majorana sur le transport électronique. Nous étudions un îlot supraconducteur où plusieurs de ces fermions existent. Ce système pourrait être l'un des composants élémentaires d'un éventuel ordinateur quantique. Les fermions de Majorana changent les statistiques d'échange des porteurs de charges, ce qui se traduit par une fractionnalisation de la conductance. Celle-ci se révèle très robuste face aux anisotropies et autres perturbations. Nous étendons les études précédentes au cas où le nombre d'électrons dans la boîte peut fluctuer, et montrons l'équivalence de ce problème avec le modèle Kondo à plusieurs canaux. Nous réinterprétons alors ce modèle en terme du déplacement d'une particule dans un réseau fictif dissipatif. / In this thesis, we study theoretically different aspects of topological systems. These models present resilient properties due to a non-trivial topology of their band structures, and in particular exotic edge excitations such as Majorana fermions.Entanglement entropy and entanglement spectrum have been fundamental to the study of these systems and of gapless systems in general, but are difficult to measure experimentally. Bipartite charge fluctuations were proposed as a weak measurement of this entanglement, in particular for one-dimensional gapless phases. We extend previous results on standard Luttinger Liquids to generic families of one- and two-dimensional non-interacting topological systems. Through exact computations, we show that their critical points are characterized by universal coefficients that reveal the topological aspect of the transitions. In two dimensions, the Dirac cones give quantized contributions to the fluctuations and various correlation functions. These contributions depend on their winding numbers, allowing for a precise determination of the topological structure of the gapless points. A volume law is also present and linked to the Quantum Fisher information, with characteristic non-analyticities at the phase transitions.In a second time, we include interactions and show that some of these signatures are preserved in topological superconductors even in their presence. Through analytical (bosonization, renormalization group) and numerical (exact diagonalization and DMRG) methods, we study the phase diagram of two Coulomb-coupled topological superconducting wires. We are interested in their behavior when the interactions are strong enough to break the topological protection: the interplay between unconventional superconductivity and interactions leads to exotic phases. We show the appearance of phases spontaneously breaking the time-reversal symmetry, with non-trivial orbital currents, and of an unusual gapless phase that is the extension of two critical interacting Majorana modes.Finally, we are interested in electronic transport mediated by Majorana fermions. We study a floating superconducting island carrying several such impurities. This device is thought to be a potential building block for a quantum computer. The Majorana fermions affect the statistics of the charge carriers, which leads to very resilient fractionalized transport. We extend previous studies to the charge degenerate case, where the total number of fermions in the island is not fixed, and map it to the well-known Multi-Channel Kondo model at large interaction. We reinterpret this standard model in terms of a particle moving in a highly dimensional, dissipative lattice.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第19494号 / 理博第4154号 / 新制||理||1597(附属図書館) / 32530 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 川合 光, 教授 畑 浩之, 教授 田中 貴浩 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20889号 / 理博第4341号 / 新制||理||1623(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 戸塚 圭介, 教授 川上 則雄, 教授 佐藤 昌利 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Entanglement is a key resource in many quantum information schemes andin the last years the research on multi-qubit entanglement has drawn lots ofattention. In this thesis the experimental generation and characterization ofmulti-qubit entanglement is presented. The qubits are implemented in the polarizationdegree of freedom of photons and we have prepared genuine entangledstates of two, four and six photons. We emphasize that one type of states thatwe produce are invariant entangled states, remaining unchanged under simultaneousidentical unitary transformations of all their individual constituents.Such states can be applied to e.g. decoherence-free encoding, quantum communicationwithout sharing a common reference frame, quantum telecloning,secret sharing and remote state preparation schemes.In the experimental implementation we use a single source of entangledphoton pairs and extract the first, second and third order parametric downconversion.The multi-order processes are not entirely spontaneous, as we getthe right states utilizing bosonic emission enhancement due to indistinguishability.Despite the achievement of six-photon entangled states, is the setupcompletely free from interferometric overlaps making it robust and contributingto high fidelities of the generated states. The analysis results of our experimentalstates are in very good agreement with theory and also show very highvisibilities in their correlations.

In a world where halting climate breakdown is becoming more and more urgent by the minute, so too does the media industry need to deliver its contribution to change. Especially since innovation - a carrier of change - is seen as one of the main pillars of this field. Even more since anthropocentrism – a mind-set of particular harm towards the current Earth crisis – still seems to prevail this pillar. In an ambition to contribute to the urgent and necessary need to halt climate breakdown, this research delves into design thinking, one of the currently popular and established innovation processes, and investigates how it can become non-anthropocentric. Insights are drawn from observations and interviews with several designers who have engaged in the journey to move themselves, their practise and their results towards non-anthropocentrism. Analysing these, it becomes clear that non- anthropocentric design is about embodying an entanglement of species. This is achieved through understanding that we are entangled, by acting in collaboration with diverse fields and through being humble. Moreover, the paper suggests design thinking can become non-anthropocentric - shifting its focus from human to earthling needs - through thickening its current converging phases with speculative scenarios. These should highlight the additional needs of and implications for a diverse set of earthlings. In this manner the scenarios manifest the entanglement. The exercise is done best in collaboration with stakeholders from a diverse set of fields and with help from posthumanist perspectives, real-world entanglement examples, surprise and unifying language. Also, doing justice to the complexity of the entanglement and the challenging nature of this exercise, the scenarios need to be continuously re-evaluated. This demands design thinking to move away from its focus on processes within the scope of a project towards a focus on long-term service-based relationships within the scope of the on-going entanglement. Product-as-a-service business models could potentially make this viable. / Behovet av att lindra och minimera effekterna av klimatförändringarna blir allt tydligare för var dag som passerar. Medieindustrin måste bidra till omställningen av samhället. I synnerhet eftersom innovation – en pådrivare av förändring – ses som en av huvudpelarna inom medieindustrin. Innovation som en gren inom medieindustrin genomsyras dock av den antropocentriska världsbilden, en världsbild som anses bidra till de nuvarande miljökriserna. I ett försök att bidra till att minimera effekterna av klimatförändringarna dyker denna studie ner i ’design thinking’, en i stunden populär och etablerad innovationsprocess, för att undersöka hur denna kan bli icke antropocentrisk. Insikter hämtas från observationer och intervjuer med flertalet designers med erfarenhet av icke antropocentrisk världsbild inom designprocesser. Analys av dessa visar att icke antropocentrisk design handlar om att förkroppsliga en väv av olika arter. Det uppnås genom en förståelse för att vi är en komplex väv, genom att agera tillsammans med olika aktörer och genom att vara ödmjuk. Vidare föreslår artikeln att ”design thinking” kan bli icke antropocentrisk dvs skifta fokus från mänskliga behov till ’earthling’-behov genom att kontextualisera de konvergerande faserna i ’design thinking’ med spekulativa scenarier. Dessa scenarier borde visa på behov och implikationer för många olika ’earthlings’. På så vis manifesteras väven av dessa scenarier. Denna handling lämpar sig bäst i samarbete med andra aktörer från många olika discipliner och med hjälp från posthumanistiska perspektiv, verkliga exempel på komplexiteten och sambanden inom väven, överraskning och ett enande språkbruk. De olika scenarierna måste konstant omvärderas för att göra vävens komplexitet och den utmanande karaktären av handlingen rättvisa. Detta kräver att ’design thinking’ fokuserar på långsiktiga serviceorienterade relationer inom ramen för väven istället för att fokusera på processer inom ramen för specifika projekt. ’Product-as-a-service’ affärsmodell skulle potentiellt kunna göra detta genomförbart.

Spontaneous parametric down-conversion (SPDC) is a nonlinear optical process in which an incident field known as the pump interacts with a nonlinear crystal to produce two output fields known as signal and idler. Due to the conservation of energy and momentum, these output fields are entangled in the temporal and spatial degrees of freedom. The gain, which represents the strength of the interaction, increases in direct proportion to the strength of the pump field. In the low-gain regime, the generated field is an entangled two-photon state. This regime continues to be routinely employed in fundamental quantum optics experiments and quantum technologies. In the high-gain regime, the generated field is a multiphoton entangled state known as a bright squeezed vacuum. The goal of this thesis is to theoretically and experimentally characterize the spatial correlations present in high-gain SPDC. In order to characterize the spatial correlations between the generated fields, we utilize the Schmidt decomposition formalism. In this study, we examine the evolution of the Schmidt modes and spectrum with increasing pump amplitude. Our work shows that the Schmidt modes expand marginally in size, and the Schmidt spectrum narrows with respect to increasing gain. The narrowing of the Schmidt spectrum, as quantified by a decrease in the Schmidt number, indicates a gradual decrease in spatial entanglement.