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Quantum entanglement is widely renounced as one of the most fundamental concepts of quantum mechanics. Such phenomenon exhibit non-local interaction properties which cannot be explained classically. In this thesis, we address a number of problems associated with creating, transferring and engineering of entanglement between two separate parties. The work is motivated by a desire to better understand the dynamics of entanglement between systems. In particular, the research is mainly focused on the study of the dynamics of the well known maximally entangled Bell state under different influences such as decoherence and inter-qubit coupling. We show the connection between coherence and entanglement using the system sub jected to decoherence. We also confirm the transfer of entanglement between completely isolated partite using the double Jaynes-Cummings model. Based on this result, we propose a new conservation criterion proven to be general for single excitation systems. Such conservation criterion are then compared and extended to a general N qubit systems. In addition, an attempt is made to evaluate entanglement conservation rules for the EPR- like multipartite entanglement. We also describe a new technique for solving entanglement in the top-down way ignoring physical setup.

Quantum entanglement is widely renounced as one of the most fundamental concepts of quantum mechanics. Such phenomenon exhibit non-local interaction properties which cannot be explained classically. In this thesis, we address a number of problems associated with creating, transferring and engineering of entanglement between two separate parties. The work is motivated by a desire to better understand the dynamics of entanglement between systems. In particular, the research is mainly focused on the study of the dynamics of the well known maximally entangled Bell state under different influences such as decoherence and inter-qubit coupling. We show the connection between coherence and entanglement using the system sub jected to decoherence. We also confirm the transfer of entanglement between completely isolated partite using the double Jaynes-Cummings model. Based on this result, we propose a new conservation criterion proven to be general for single excitation systems. Such conservation criterion are then compared and extended to a general N qubit systems. In addition, an attempt is made to evaluate entanglement conservation rules for the EPR- like multipartite entanglement. We also describe a new technique for solving entanglement in the top-down way ignoring physical setup.

Quantum entanglement is widely renounced as one of the most fundamental concepts of quantum mechanics. Such phenomenon exhibit non-local interaction properties which cannot be explained classically. In this thesis, we address a number of problems associated with creating, transferring and engineering of entanglement between two separate parties. The work is motivated by a desire to better understand the dynamics of entanglement between systems. In particular, the research is mainly focused on the study of the dynamics of the well known maximally entangled Bell state under different influences such as decoherence and inter-qubit coupling. We show the connection between coherence and entanglement using the system sub jected to decoherence. We also confirm the transfer of entanglement between completely isolated partite using the double Jaynes-Cummings model. Based on this result, we propose a new conservation criterion proven to be general for single excitation systems. Such conservation criterion are then compared and extended to a general N qubit systems. In addition, an attempt is made to evaluate entanglement conservation rules for the EPR- like multipartite entanglement. We also describe a new technique for solving entanglement in the top-down way ignoring physical setup.

Orientador: Antonio Vidiella Barranco / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-31T02:56:15Z (GMT). No. of bitstreams: 1 Decordi_GustavoLazero_D.pdf: 2456755 bytes, checksum: 42a17eacb2e1a86e81888e48272ed08e (MD5) Previous issue date: 2016 / Resumo: Estudamos nesta tese, sistemas quânticos compostos sob a influência de ambientes externos. Na primeira parte do trabalho, investigamos um sistema de dois qubits interagentes, estando um deles isolado e o outro acoplado a um banho térmico. Analisamos os efeitos da temperatura do banho sobre a dinâmica do sistema de dois qubits. Com essa finalidade, empregamos dois modelos distintos da interação sistema-ambiente: i) um modelo microscópico, no qual a equação mestra é obtida levando-se em conta o acoplamento entre os qubits na dedução do termo dissipativo, ii) um modelo fenomenológico, no qual o termo dissipativo é simplesmente adicionado ao termo unitário da equação de evolução do operador densidade. Obtemos soluções analíticas para os modelos, o que permitiu estudá-los em um intervalo considerável do acoplamento entre os qubits. Dedicamos a segunda parte do trabalho ao estudo de um sistema quântico em particular acoplado a um pequeno ambiente. Neste contexto, resolvemos exatamente o modelo da interação radiação-matéria conhecido como modelo de Tavis-Cummings a dois átomos. De posse das soluções, obtidas em circunstâncias bastante gerais e até então não encontradas na literatura, investigamos os efeitos oriundos da interação de um pequeno ambiente (átomo em estado de mistura estatística) sobre a dinâmica do subsistema composto pelo outro átomo acoplado ao modo do campo eletromagnético. Nós mostramos que propriedades não-clássicas associadas ao sistema principal podem ser significativamente degradadas pela ação do ambiente quando o átomo 2 está acoplado de maneira resonante ao campo. Encontramos que o comportamento não-clássico do sistema pode ser restaurado a medida que dessintonizamos o campo da frequência de transição do átomo 2, o ambiente / Abstract: We study in this thesis composite quantum systems under the influence of external environments. In the first part of this work, we investigate a two qubit interacting system having one of them isolated and the other coupled to a thermal bath. We analyze the effect of the temperature of the bath on the dynamics of the two qubit system. In order to do that, we consider two different models of system-reservoir interaction: i) a "microscopic" model, in which the master equation is derived taking into account the interaction between the two subsystems (qubits), ii) a "phenomenological" approach, in which the master equation consists of a dissipative term added to the unitary evolution term. We show that in the strong coupling regime between the subsystems (qubits), the expected thermal equilibrium steady state for the two-qubit system naturally arises in the framework of the microscopic model, while in the phenomenological approach it is obtained a steady state density operator which is not correct. Furthermore, the differences are even more profound in the weak coupling regime, when the models give rise to opposite behaviors with regard to the linear entropy of qubit 1. At the context of quantum systems coupled to environments with few degrees of freedom, we solve analytically the matter-radiation interaction model known as two atom Tavis-Cummings Model. With the solutions at hand, achieved in general circumstances until the present not found in literature, in which the constituent atoms may be coupled with different strengths to the field and also have different frequency detunings, we study the effects that arise from the interaction of a small environment (atom in a statistical mixture state) with the other atom coupled to an oscillator (cavity mode). We show that nonclassical features associated to the main system may be significantly degraded by the action of the small environment, if atom 2 is resonantly coupled to the field. We also demonstrate that the nonclassical behaviour of the system may be restored if we detune the field from the transition frequency of atom 2, the environment / Doutorado / Física / Doutor em Ciências / 899872/2011 / CAPES

In the main part of this thesis I study the relaxation mechanisms of charge carriers in silicon nanocrystals in SiO2 matrix. One of the potential applications of these structures lies in photovoltaics, specifically in construction of all-silicon tandem solar cells. I studied the dynamics of carriers in these structures by methods of ultrafast spectroscopy which helped to unravel the microscopic behaviour of carriers, their transport, localization etc. Furthermore I investigated the doping of such structures as the technology of doping is crucial for manufacture of pn- junctions which are the core component of solar cells. At the end I delve into the dissipative Jaynes-Cummings model by mathematical modeling and theoretical calculations which describes among others microlasers and as such comes under a field of cavity quantum electrodynamics.

This thesis is devoted to optical properties of Aharonov-Bohm quantum rings in external electromagnetic fields. It contains two problems. The first problem deals with a single-electron Aharonov-Bohm quantum ring pierced by a magnetic flux and subjected to an in-plane (lateral) electric field. We predict magneto-oscillations of the ring electric dipole moment. These oscillations are accompanied by periodic changes in the selection rules for inter-level optical transitions in the ring allowing control of polarization properties of the associated terahertz radiation. The second problem treats a single-mode microcavity with an embedded Aharonov-Bohm quantum ring, which is pierced by a magnetic flux and subjected to a lateral electric field. We show that external electric and magnetic fields provide additional means of control of the emission spectrum of the system. In particular, when the magnetic flux through the quantum ring is equal to a half-integer number of the magnetic flux quantum, a small change in the lateral electric field allows tuning of the energy levels of the quantum ring into resonance with the microcavity mode, providing an efficient way to control the quantum ring-microcavity coupling strength. Emission spectra of the system are calculated for several combinations of the applied magnetic and electric fields.

Made available in DSpace on 2014-07-29T15:07:09Z (GMT). No. of bitstreams: 1 dissertacao_Alexandre Divino.pdf: 736654 bytes, checksum: 2b8069070ebe78eef1b634051df5d432 (MD5) Previous issue date: 2009-02-20 / In this work we have studied the two photon Jaynes-Cummings model to describe the interaction of a three-level atom in the configuration with a single-mode of a cativy-field. We have used the effetive and full microscopic Jamiltonian approach to compare the results obtained in these tow descriptions. We employed the two-photon Jaynes-Cummings model int the full microscopic Hamiltonian context to implement schemes to quantuam entanglement swapping, for approximate and conditional quantuam teleportation for an unknown atomic state, for a superposition of zero- and two photon states. Both schemes were implemented using no measurement in the Bell base states. / Neste trabalho estudamos o modelo Jaynes-Cummings de dois fótons para descrever a interação de um átomo de Rydberg na configuração (ladeira) de três níveis com único modo do campo eletromagnético. A descrição deste sistema foi obtida usando o hamiltoniano efetivo e também o hamiltoniano microscópico completo, com o objetivo de compararmos resultados obtidos nas suas descrições. No modelo de Jaynes-Cummings de dois fótons descrito pleo hamiltoniano microscópico completo propusemos esquemas para realização de troca de emaranhamento quântico e teletransporte quântico aproximado e condicional de estados atômicos desconhecidos bem como estados de superposição de zeros e dois fótons do campo. Esses dois esquemas foram realizados sem uso de medida na base dos estados de Bell.

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