Le travail proposé dans cette thèse est basé sur des expérience de corrélation de photons faites sur un émetteur de photon unique semi conducteur: une boite quantique de CdSe dans un nanofil de ZnSe. La première démonstration d'émission de photons unique d'une boite quantique épitaxiée à température ambiante y est présentée. Pour expliquer ce résultat, nous avons étudie expérimentalement et théoriquement l'efficacité de couplage exciton-phonon et ses conséquences sur l'intensité de l'exciton avec la température. Nous présentons également des résultats optiques portant sur la robustesse de cette structure à haute température. La technique de corrélation de photons est également appliquée sur des boites quantiques chargées. la présence du exciton chargé nous a permis de sondé la structure fine du trio excité, de décrire ses processus de relaxations et d'obtenir une mesure direct du temps de spin flip du trou sur l'état p. Des indication sont également données sur la nature possible du dopage. Nous avons aussi étudié la diffusion spectrale de l'émetteur causée par les fluctuations électroniques de son environnement. Par un travail théorique nous montrons comment interpréter l'effet de l'élargissement phonon de la raie homogène, (processus poissonien) combiné avec l'effet de la diffusion spectral (processus markovien) sur la fonction de corrélation de la demi-raie. Grâce à l'expérience, nous concluons sur la statistique de l'énergie d'émission de l'émetteur à haute température. Nous appliquons cette théorie sur les nanofils et interprétons les dépendances en température et en puissance des fluctuations de l'environnement grâce au modèle de Kubo-Anderson. / The work proposed in this thesis is based on photon correlation experiments performed on a semi-conductor single photon emitter: CdSe/ZnSe nanowire quantum dot. Is presented the first demonstration of single photon emission at room temperature from an epitaxied quantum dot. To explain this result we investigated by a theoretical and experimental study, the exciton-phonon coupling efficiency and its consequence on the exciton luminescence intensity with temperature. We also present optical results on the robustness against temperature of this structure. Photon correlations techniques are also applied on charged quantum dots. Presence of the charged biexciton allowed to probe the fine structure of the excited trion, to describe its carrier relaxation processes, and to obtain a direct measurement of the p-shell hole spin flip time. Indications are also given on the possible doping nature. We also investigated spectral diffusion of the emitter caused by electronic fluctuations of the environnement. By a theoretical work, we show how to model the effect of the homogeneous phonon broadening, (poissonian emission energy process) combined with the spectral diffusion effect (markovian emission energy process) on the half line autocorrelation function. Thanks to experiments, We conclude on the statisic of the emission energy of the emitter at high temperature. We apply this theory on CdSe/ZnSe nanowire quantum dots and interpret temperature and power dependance of the environnement fluctuation thanks to the Kubo-Anderson Model.

Cette thèse porte sur les effets d'optique quantique avec des atomes artificiels semiconducteurs. Dans un premiers temps, on fait une étude théorique où un émetteur unique est couplé à un guide d'onde unidimensionnel. Ce système permets la propagation libre de la lumière en préservent la sensitivité au niveau d'un photon unique, ce que a motivé des propositions pour faire des portes logiques et des transistors au photon unique. Un schéma pour observer l'émission stimulée au niveau d'un photon unique dans cet environnement unidimensionnel est proposé, en utilisant un émetteur excité (e.g. une boîte quantique) et une pompage classique (laser). On montre que l'émission se produit dans le mode stimulée et que la population atomique fait des oscillations de Rabi classiques. Ensuite, la dynamique complètement quantique est décrite, où un paquet avec un seul photon interagit avec l'atome initialement excité. Dans cette nouvelle condition, la stimulation est irréversible, i.e., les populations atomiques ne réalisent pas des oscillations. Cet effet est optimal dans le cas où le paquet est trois fois plus court qu'un paquet spontanément émis par le même atome. On démontre comment utiliser l'émission stimulée irréversible optimale pour produire des clones quantiques universels. Le même dispositif peut être utilisé aussi bien pour produire des paires des photons complètement intriqués, si le paquet du photon initial est suffisamment étendu. Dans un deuxième moment, nous nous sommes intéressés aussi au spectre d'émission spontanée d'une boîte quantique semiconductrice en couplage faible avec une microcavité. Ce système mets en évidence l'effet d'alimentation de la cavité, où la boîte émet spontanément à la fréquence de la cavité, même si cela est bien désaccordé. L'influence des phonons pour le mécanisme d'alimentation de la cavité est analysée. Une importante distorsion du spectre apparent de la cavité, induit pour la présence des phonons, est démontrée. Les effets étudiés sont topiques et peuvent être implémenté avec des dispositifs semiconducteurs de l'état de l'art. / The thesis focuses on quantum optical effects in semiconducting artificial atoms. We first investigate theoretically a single emitter coupled to a one-dimensional waveguide. This system allows for light propagation while preserving sensitivity at the single-photon level, which has motivated proposals for quantum gates and single-photon transistors. A scheme to monitor stimulated emission at the single-photon level in this one-dimensional open space is proposed, using an excited emitter (e.g. a quantum dot) and a classical pump (laser). We show that light is emitted in the stimulating mode and that the atom performs classical Rabi oscillation. The fully quantum dynamics is also explored, where a single-photon packet interacts with an initially excited emitter. In contrast with the case of a classical pump, stimulation by a single photon is irreversible, i.e., no oscillation takes place. Stimulation is optimal for a packet three times shorter than the spontaneously emitted one. We show how this optimal irreversible stimulated emission can be applied to perform universal quantum cloning. The same device provides either optimal quantum cloning or maximally entangled photon pairs, depending only on the size of the incoming packet. In the second part of the thesis, we investigate the spontaneous emission spectrum of a semiconducting quantum dot weakly coupled to a microcavity. In particular, we address the problem of cavity feeding, where the quantum dot spontaneously emits photons at the frequency of an off-resonance cavity. The influence of phonons in the cavity feeding mechanism is analysed. An important distortion of the apparent cavity peak induced by the presence of phonons is demonstrated. These effects are topical and can be implemented in state-of-the-art semiconducting devices.

Cette thèse décrit une série de travaux réalisés dans le contexte des qubits de spins, allant de l'utilisation de ces qubits pour stocker de l'information à leur utilisation comme détecteurs ultra-sensibles. Nous utilisons des hétérostructures semi-conductrices d'arséniure de gallium dans lesquelles un électron unique peut être isolé au sein d'un piège électrostatique, une boîte quantique. Le spin de cet électron peut être utilisé pour encoder de l'information, et la boîte quantique contenant ce spin unique est alors vue comme un qubit (quantum bit). Au cours de cette thèse nous démontrons la réalisation expérimentale du transport d'un électron unique le long d'un circuit fermé au sein d'un système composé de quatre boîtes quantiques couplées. En considérant l'interaction spin-orbite, cette expérience ouvre la voie vers des manipulations cohérentes de spins utilisant des effets topologiques. Dans le contexte de l'ordinateur quantique et des qubits de spins, nous étudions les portes logiques à deux qubits. Dans le cadre de deux boîtes quantiques couplées par une barrière tunnel, nous démontrons qu'en contrôlant localement le champ magnétique, la porte logique à deux qubits évoluent de la porte SWAP à la porte C-phase. Nous démontrons ainsi la faisabilité d'une porte C-phase. Finalement nous montrons l'utilisation d'un qubit de spin comme un détecteur de charge ultrasensible. Un singlet-triplet qubit est un système quantique qui peut être réglé de manière à être extrêmement sensible à l'environnement électrostatique. Nous démontrons la faisabilité d'un tel détecteur, et nous montrons qu'il peut être utilisé pour détecter un électron unique. / In this thesis we described a series of experimental works, which have been realized in the context of spin qubits, going from their use as information carriers to their use as very sensitive detectors. We use AlGaAs semiconducting heterostructures in which a single electron can be isolated in an electrostatic trap, the so-called quantum dot. The electron spin can be used in order to encode information, and the quantum dot containing this electron can therefore be seen as a qubit (quantum bit). During this thesis we demonstrate the first experimental realization of a single electron transport along a closed path inside a system composed of four coupled quantum dots. By considering spin-orbit interaction, this experiment opens the way toward coherent topological spin manipulations. In the context of quantum computing and spin qubits, we study the two-qubit gates. By considering two tunnel coupled quantum dots, we demonstrate by controlling the local Zeeman splitting that the natural two-qubit gate for spin qubits evolves from the SWAP gate to the C-phase gate. This work demonstrates the feasibility of the C-phase gate. Finally we use spin qubits as very sensitive detectors. A singlet-triplet qubit is a quantum system which can be tuned in order to be very sensistive to the electrostatic environment. Here we report the use of such a qubit to detect a single electron transported next to the detector.

Submitted by GEOVANE MODENA PEREIRA null (geovanemodena@hotmail.com) on 2018-02-10T03:04:38Z No. of bitstreams: 1 Dissertação Geovane - Criptografia de Qubits de Férmions de Majorana por meio de Estados Ligados no Contínuo.pdf: 7524654 bytes, checksum: 0bd9409e8fa9c0c2da9190e44f4cfa33 (MD5) / Approved for entry into archive by Ana Paula Santulo Custódio de Medeiros null (asantulo@rc.unesp.br) on 2018-02-14T16:11:32Z (GMT) No. of bitstreams: 1 pereira_gm_me_rcla.pdf: 7420427 bytes, checksum: 0a0aec5beec2ecdd26883e0f4524844f (MD5) / Made available in DSpace on 2018-02-14T16:11:32Z (GMT). No. of bitstreams: 1 pereira_gm_me_rcla.pdf: 7420427 bytes, checksum: 0a0aec5beec2ecdd26883e0f4524844f (MD5) Previous issue date: 2017-12-01 / Nós investigamos teoricamente uma cadeia topológica de Kitaev conectada a dois pontos quânticos (QDs) hibridizados a terminais metálicos. Neste sistema, observamos o surgimento de dois fenômenos marcantes: (i) uma decriptografia do Férmion de Majorana (MF), que é detectado por meio de medições de condutância devido ao estado de vazamento assimétrico do qubit de MFs nos QDs; (ii) criptografia desse qubit em ambos os QDs quando o vazamento é simétrico. Em tal regime, temos portanto a criptografia proposta, uma vez que o qubit de MFs separa-se nos QDs como estados ligados no contínuo (BICs), os quais não são detectáveis em experimentos de condutância. / We theoretically investigate a topological Kitaev chain connected to a double quantum-dot (QD) setup hybridized with metallic leads. In this system, we observe the emergence of two striking phenomena: i) a decrypted Majorana Fermion (MF) - qubit recorded over a single QD, which is detectable by means of conductance measurements due to the asymmetrical MF-leaked state into the QDs; ii) an encrypted qubit recorded in both QDs when the leakage is symmetrical. In such a regime, we have a cryptography-like manifestation, since the MF-qubit becomes bound states in the continuum, which is not detectable in conductance experiments.

Neste trabalho, foi estudado a aplicação de novas heteroestruturas semicondutoras para detecção de radiação na região do infravermelho médio. Pontos quânticos de submonocamada, detectores de cascateamento quântico e pontos quânticos de InAlAs foram testados como opção para corrigir as deficiências em responsividade, corrente de escuro e temperatura de operação, comuns nas heteroestruturas convencionais baseadas em poços quânticos e pontos quânticos de InAs obtidos no regime de crescimento Stranski-Krastanov. Também foi projetado, fabricado e testado um circuito eletrônico de leitura de sinal misto para integração com matrizes de sensores e produção de imagens. Esse tipo de circuito possui uma série de vantagens em relação aos dispositivos convencionais que costumam ser completamente analógicos. / In this work, we studied the application of new types of semiconductor heterostructures for mid-infrared detection. Submonolayer quantum dots (SML-QDs), quantum-cascade detectors (QCDs) and InAlAs quantum dots were tested as an option to circumvent the common shortcomings of responsivity, dark current and operating temperature of the usual heterestructures based on quantum wells (QWs) and InAs Stranski-Krastanov quantum dots. We also designed, fabricated and tested a mixed-signal read-out circuit aiming the fabrication of focalplane arrays (FPAs) for applications to infrared imaging. This kind of architecture has several advantages over a fully analog design.

Esta tese é composta por duas partes. Na primeira parte, os efeitos da interação elétron-elétron nas configurações do estado fundamental de dois anéis quânticos acoplados (CQRs) são estudados. Os CQRs podem formar um novo tipo de molécula artificial, onde o raio dos anéis juntamente com a distância entre os anéis, são novos parâmetros ajustáveis que fornecem novos graus de liberdade para controlar a estrutura eletrônica destas moléculas. Através da bem estabelecida teoria do funcional densidade dependente de spin, as configurações ou fases do estado fundamental dos CQRs com alguns elétrons são determinadas. Uma rica variedade de fases para o estado fundamental destas novas moléculas artificiais é encontrada para sistemas contendo até N=13 elétrons. Para CQRs com N menor ou igual a 8 são obtidas qualitativamente configurações para o estado fundamental similares às dos pontos quânticos acoplados (CQDs). As novas configurações eletrônicas aparecem para N maior ou igual a 9. Na segunda parte desta tese é desenvolvido um método numérico para estudar o espalhamento eletrônico através de um ponto quântico com N-elétrons confinados. Considera-se que o ponto quântico está imerso num sistema bidimensional ou confinado em um canal unidimensional. As taxas de espalhamento são obtidas resolvendo iterativamente a equação de Lippmann-Schwinger incluindo a interação elétron-elétron entre o elétron incidente e os N-elétrons confinados dentro do QD. Para exemplificar, este método é aplicado para um elétron externamente injetado sobre um QD contendo um único elétron. As taxas de espalhamento elástico, inelástico e de spin-flip são obtidas. Os efeitos da interação de troca no espalhamento eletrônico e transporte através do QD são analisados.Também são considerados os processos do espalhamento multi-canal neste sistema e suas influências nas propriedades de transporte. / This thesis is composed of two parts. In the first part, we study the effects of electron-electron interactions on the ground state configurations of two vertically coupled quantum rings (CQRs). The CQRs can form a new type of artificial molecule (AM) where the ring radius together with the inter-ring distance are new tunable parameters providing new degrees of freedom to modulate and control the electronic structure of the artificial ring shaped molecules. In this work, we apply the well established spin-density functional theory to study the ground state configurations or phases of few-electron CQRs. A rich range of ground state phases of these new quantum ring AMs is uncovered for systems containing up to N = 13 electrons. For CQRs with N less or equal to 8 we found qualitatively similar ground state phases as for coupled quantum dots (CQDs). Novel phases appear for N greater or equal to 9. In the second part of this thesis, we develop a numerical method to study the electron scattering through an occupied quantum dot (QD) with a few electrons. The QD is considered embedded in a two-dimensional system or confined in a one-dimemsional channel. An external electron is injected and scattered through the QD. The scattering rates are obtained by solving iteratively the Lippmann-Schwinger equation including the electron-electron interactions between the incident electron and the N-electrons confined in the QD. As an example, we apply this model for an externally injected electron through a QD with one electron inside. The elastic, inelastic, and spin-flip scattering rates are obtained. The effects of electron exchange interaction on the electron scattering and transport through the QD are analyzed. We also show the multi-channel scattering processes in such systems and their influences on the electron transport properties.

O objetivo deste trabalho é examinar os efeitos causados pela interação elétron-fônon em pontos quânticos semicondutores polares. Primeiramente, nós apresentamos cálculos detalhados da taxa de espalhamento e do tempo de relaxação eletrônico em pontos quânticos simples (Single Quantum Dot - SQD) e em dois pontos quânticos acoplados (Coupled Quantum Dots - CQDs) devido à interação entre o elétron e os fônons longitudinais acústicos (LA) na presença e na ausência de campos externos, magnético ou elétrico. O regime de energia usado no cálculo do espalhamento eletrônico foi escolhido de forma que os fônons LA dominam o processo de espalhamento. Nós verificamos que na ausência de campo externo, a taxa de espalhamento do elétron por fônons LA entre dois níveis específicos é essencialmente determinada pela diferença de energia entre estes dois níveis. Observamos que um campo magnético modula fortemente a taxa de espalhamento. Verificamos que o processo de relaxação via multicanais desempenha um papel essencial no mecanismo de relaxação do elétron de estados excitados para o estado fundamental. Um campo magnético externo aumenta ainda mais a relaxação através de transições indiretas. Também fizemos um estudo teórico dos efeitos da interação elétron-fônons longitudinais ópticos (LO) em dois pontos quânticos acoplados compostos de InAs/AlInAs. Fizemos cálculos para o polaron ressonante num regime onde a energia de confinamento do elétron é comparável a energia do fônon L0 utilizando o formalismo da função de Green e teoria de perturbação considerando temperatura zero e finita. Observamos uma renormalização do estado fundamental obtida devido a absorção de fônons virtuais para uma temperatura T > O. Discutimos os efeitos do tunelamento entre os pontos quânticos e a sua influência nas propriedades eletrônicas e analisamos o espectro de absorção óptica neste sistema. Verificamos modificações nos orbitais eletrônicos como resultado direto do tunelamento assistido por fônons. Finalmente, avaliamos os efeitos da interação elétron-fônons L0 na densidade de estados do elétron confinado em pontos quânticos utilizando dois modelos distintos: Um modelo não-perturbativo e o formalismo da função de Green. Estudamos cada método separadamente e avaliamos a densidade de estados como função da temperatura e do confinamento lateral. Consideramos um sistema com apenas dois níveis eletrônicos de energia e comparamos os dois métodos avaliando as suas diferenças básicas. Utilizando o método não-perturbativo fizemos cálculos da densidade de estados para um regime de acoplamento forte entre o elétron e os fônons LO / The purpose of this work is to study effects of electron-phonons interactions in polar semiconductor quantum dots. Firstly, we present a detailed calculation on the electron-LA-phonon scattering rates and electron relaxation processes in single and coupled quantum dots in the absence and in the presence of external magnetic or electric fields. In the absence of external field, interplay among the effective confinement lengths in different directions as well as the phonon wavelength leads to a strong oscillation of the LA-phonon scattering rate between two levels. In other words, the scattering depends strongly on the geometry and confinement potential of the quantum dot. An external magnetic field also strongly modulates the scattering rate in severa1 orders of magnitude. The magnetic field induced effects are very similar in single quantum dot (SQD) and coupled quantum dots (CQDs) where the effective confinement strength in the x-direction affects strongly the scattering rate. However, we find that the multiple relaxation process plays an essential role for electron relaxing from the excited states to ground state both in single and coupled quantum dots. Including all possible relaxation channels, an external magnetic field enhances the relaxation through indirect transitions. Secondly, we present a theoretical study on the effects of electron-LO-phonon interaction in two coupled stacked InAs/InAIAs quantum dots. The contribution of resonant and nonresonant electron-LO-phonon coupling to the polaron states are obtained in the framework of t he Green function formalism and the perturbation approach at zero and finite temperatures. Ground state renormalization is found due to virtual phonon absorption at T > O. Tunneling effects between the dots have been addressed and their influente on the electronic properties and optical absorption are analyzed. Topological modifications of electronic orbitals are found as a result of phonon-assisted tunneling. Finally, we investigate the effects of electron-LO-phonon interaction on the electron density of states in quantum dots using two distinct models. A non-perturbative model and the Green function formalism. Within the non-perturbative model, we consider only two electronic levels in a quantum dot interacting to LO-phonons. An exact solution is obtained for the polaron states and spectral function. We evaluate the density of states in the regime at zero and finite temperature for severa1 values of the lateral confinement. We compare the density of states obtained within the two models. Furthermore, we study the polaron effects in strong electron-LO-phonon coupling regime based on the non-perturbative model

Les conjugués QD-sdAbs sont des nano-sondes qui associent un quantum dot (QD) et des anticorps de domaine simple (sdAbs). Ces nano-sondes fluorescentes permettent des immunomarquages sur coupes tissulaires et sur cellules. L’objectif de ce travail est de montrer l’intérêt de l’excitation multi-photonique pour la détection et la localisation très spécifiques de biomarqueurs tumoraux.L’excitation multi-photonique des nano-sondes QD570-sdAb anti-CEA a été étudiée, sur coupes d’appendice et de carcinome du côlon humains pour optimiser le rapport signal/auto-fluorescence. L’utilisation du QD comme capteur d’énergie d’excitation dans un modéle de FRET QD-fluorophore organique a été démontré. Un modéle innovant pour une détéction ultra spécifique du CEA sur cellules MC38 CEA par double immunomarquage spécifique pour un transfert d’énergie résonnant entre QD et Alexa Fluor à été mis en oeuvre.Les résutats montrent l’intérêt de l’excitation multi-photonique par rapport à l’excitation à 458,9 nm pour la discrimination et l’optimisation du rapport signal/auto-fluorescence. Il est 40 fois supérieur en excitation à 800 nm qu’à 458,9 nm sur les coupes étudiées.L’utilisation des conjugués QD556-sdAb anti-CEA et d’un anticorps monoclonal permet un double immunomarquage du CEA membranaire sur cellules MC38 CEA. L’utilisation du QD comme nano-capteur d’énergie d’excitation multi-photonique permet une séléctivité d’excitation et un FRET entre QD et Alexa Fluor. Ce schéma permet une détéction spectrale aisée du FRET et une localisation très spécifique et sensible du CEA membranaire. Ceci est conforté par la diminution du temps de déclin du QD556 donneur d’énergie non radiative. / The QD-sdAbs conjugates are nano-sensors that combine a quantum dot (QD) and single domain antibodies (sdAbs). These fluorescent nanoprobes allow immunostaining on tissue sections and cells. The objective of this work is to show the interest of the multi-photon excitation for the detection and highly specific location of tumor biomarkers.Multi-photon excitation of anti CEA QD570-sdAb nanoprobes was investigated on human appendix and colon carcinoma slides for specifical detection and an optimization of the signal/auto-fluorescence emission ratio. The use of QD as excitation energy sensor for a QD-organic fluorophore FRET model has been shown. An innovative model for ultra-specific detection of CEA on MC38 CEA membrane cells by double immunostaining for a resonant energy transfer between QD and Alexa Fluor has been implemented.Our results shows the great interest of the multi-photon excitation compared to 458.9 nm excitation for discrimination and optimization of the signal / autofluorescence. It is 40 times higher at 800 nm two photon excitation has 458.9 nm one photon excitation on the studied sections.The use of conjugated QD556-sdAb anti-CEA and a conventional monoclonal antibody allows a double immunostaining on CEA on MC38 CEA membrane cells. The QD is use as multi-photon excitation energy nano-sensor enables an excitation selectivity and FRET between QD and Alexa Fluor. This configuration enables easy spectral detection of FRET and a very specific and sensitive location of membrane CEA. This is reinforced by the decrease in decay time of QD556 as donor of non radiative energy.

The region between the infrared and microwave region in the electromagnetic spectrum, the Terahertz (THz) gap, provides an exciting opportunity for future wireless communications as this band has been under utilised. This doctoral work takes a two-pronged approach into closing the THz gap with low-dimensional materials. The first attempt addresses the need for a compact THz source that can operate at room temperature. The second approach addresses the need to build optical elements such as filters and modulators in the THz spectrum. Terahertz quantum cascade lasers (THz QCLs) are one of the most compact, powerful sources of coherent radiation that bridge the terahertz gap. However, their cryogenic requirements for operation limit the scope of the applications. This is because of the electron-electron scattering and heating of the 2-dimensional free electron gas which leads to significant optical phonon scattering of the hot electrons. Theoretical studies in laterally confined QCL structures have predicted enhanced lifetime of the upper state through suppression of the non-radiative intersubband relaxation of carriers, which leads to lower threshold, and higher temperature performance. Lithographically defined vertical nanopillar arrays with electrostatic radius less than tens of nm offer a possible route to achieve lateral confinement, which can be integrated into QCL structures. A typical gain medium in a QCL consists of at least 100 repeat periods, with a thickness of 6-14 micron. For practical implementation of the top-down approach, restrictions are imposed by aspect ratios that can be achieved in present dry-etching systems. Typically, for sub-200 nm radius pillars, the thickness ranges from 1-3.5 micron. It is therefore necessary to work with THz QCLs based on 3-4 quantum well active regions, so as to maximise the number of repeat periods (hence gain) within an ultra-thin active region. After an introductory chapter, Chapter 2 presents a theoretical treatise on the realistic electrostatic potential in a lithographically defined nanopillar by scaling from a single quantum well (resonant tunnelling diode) to a THz QCL. Chapter 2 also discusses, the effect of lateral confinement on the intersubband states and the plasmonic mode in a THz QCL. One of the key experimental challenges in scaling down from QCLs to quantum-dot cascade lasers is the electrical injection into the nanopillars. This involves insulation and planarisation of the high aspect-ratio nanopillar arrays. Furthermore, the choice of the planarising layer is critical since it determines the loss of any optical mode. This experimental challenge is solved in Chapter 3. Chapter 4 presents the electro-optic performance of low-repeat period QCLs with an active region thickness that is less than 3.5 micron. Another topic of recent interest in the THz optics community is plasmonics in graphene. This is because the bound electromagnetic modes (plasmons) are tightly confined to the surface and can also be tuned with carrier concentration. Plasmonic resonance at terahertz frequencies can be achieved by gating graphene grown via chemical vapour deposition (CVD) to a high carrier concentration. THz time domain spectroscopy of such gated monolayer graphene shows resonance features around 1.6 THz superimposed on the Drude-like frequency response of graphene which may be related to the inherent poly-crystallinity of CVD graphene. Chapter 5 discusses these results, as an understanding of these features is necessary for the development of future THz optical elements based on CVD graphene. Chapter 5 finally describes how the gate tunability of THz transmission through graphene can be exploited to indirectly modulate a THz QCL. Chapter 6 presents ideas from this doctoral work, which can be developed in future to address the issues of enhanced temperature performance of THz QCLs and to realise realistic THz devices based on graphene.

Cette thèse est consacrée à l'étude théorique des propriétés de transportd'un nanodispositif comme par exemple une boîte quantique. A faible dimensionnalité,les propriétés de transport sont fortement liées à la densité d'étatsélectroniques du système, il est donc important d'utiliser une approche capablede calculer cette dernière correctement notamment en tenant comptedu confinement électronique.En utilisant le modèle d'Anderson et l'approximation de non croisementafin de calculer la densité d'états, on a pu observer et caractériser les transfertsde poids spectral pour des orbitales simplement, doublement ou triplementdégénérées. Ces transferts de poids spectral sont typiques des systèmescorrélés, mais lorsqu'une différence de potentiel est appliquée, on a pu remarquerque ces transferts se faisaient en deux temps.Dans un second temps, on a analysé les signatures du couplage de Hundincluant le terme de saut de paires dans les diagrammes de stabilité. Ces deuxtermes, provenant de l'interaction Coulombienne, modifient sensiblement lastructure des diamants de Coulomb et doivent donc être considérés lorsqu'ondéduit les paramètres microscopiques à partir du diagramme de stabilitéexpérimental.Enfin, on s'est placé dans le régime de générateur thermoélectrique, et ona utilisé le pic de Kondo comme canal de transport. Cependant l'optimisationà la fois du rendement et de la puissance en utilisant les bandes de Hubbardcomme canaux de transport est impossible. Or les particularités et les grandeurscaractérisant le pic de Kondo permettent d'une part de s'affranchirpartiellement de ce compromis mais cela permet également de générer uneplus grande puissance. / This thesis is devoted to the theoretical study of a nanodevice transportproperties, such as a quantum dot. At low dimensionality, transport propertiesare strongly related to the local density of state, it is important to use anapproach able to compute the latter properly especially tanking into accountthe electronic containment.Using the Anderson model and the non-crossing approximation to computedensity of states, we observed and characterize spectral weight transfersfor simply, doubly and triply degenerated orbitals. These spectral weighttransfers are typical of correlated systems, but when potential bias is applied,we note that these transfers occur in two stages.In a second step, we analyze Hund coupling footprint including pair hoppingin stability diagrams. These two terms, from the Coulomb interaction,substantially alter the Coulomb diamonds structure and must be considerwhen microscopic parameters are derived from experimental stability diagrams.Finally, we placed in the thermoelectric generator regime, and we usedKondo peak as transport channel. However, optimization of both efficiencyand power output using Hubbard bands as transport channel is impossible.But the features and scales characterizing Kondo peak serve on the one handto overcome this compromise and on the other hand to generate a greaterpower output.