16 research outputs found
Greenberger-Horne-Zeilinger state generation with linear optical elements
We propose a scheme to probabilistically generate Greenberger-Horne-Zeilinger
(GHZ) states encoded on the path degree of freedom of three photons. These
photons are totally independent from each other, having no direct interaction
during the whole evolution of the protocol, which remarkably requires only
linear optical devices to work, and two extra ancillary photons to mediate the
correlation. The efficacy of the method, which has potential application in
distribited quantum computation and multiparty quantum communication, is
analyzed in comparison with similar proposals reported in the recent
literature. We also discuss the main error sources that limit the efficiency of
the protocol in a real experiment and some interesting aspects about the
mediator photons in connection with the concept of spatial nonlocality
Uma visão contemporânea de alguns conceitos da teoria quântica
In this thesis we discuss some fundamental aspects of the quantum theory from a contemporaneous point of view, where we could develop three works. In the first we analyze theoretically an atomic double-slit interferometer. It has been shown that if the energy eigenstates of the atom are correlated with its particle and wave behaviors, complementary phenomena can be measured simultaneously, indicating a reinterpretation of the complementarity principle. We also demonstrate that this experiment possesses quantum erasure properties. In the second we present a two-particle interferometer in order to analyze the way in which decoherence affects quantum interference. It has been shown how the environmental constituents, here considered as photons, can destroy the oscillations in the coincidence detection rate of the particles. Due to the temporal characteristic of this kind of interference, we name this process as quantum temporal decoherence. In the last work we study the existence of a novel complete family of exact and orthogonal solutions of the paraxial wave equation. The complex amplitude of these beams is proportional to the confluent hypergeometric functions, which we name hypergeometric modes of type-II (HyG-II). It is formally demonstrated that a hyperbolic-index medium can generate and support the propagation of such a class of beams. Since these modes are eigenfunctions of the photon orbital angular momentum, we conclude that an optical fiber with hyperbolic-index profile could take advantage over other graded-index fibers by the capacity of data transmission.Coordenação de Aperfeiçoamento de Pessoal de NÃvel Superior - CAPESNesta tese discutimos alguns aspectos fundamentais da teoria quântica de um ponto de vista mais contemporâneo, onde também pudemos desenvolver três trabalhos. No primeiro analisamos teoricamente um interferômetro de fenda dupla para átomos. Mostramos que se os autoestados de energia do átomo estão correlacionados com os comportamentos de partÃcula e de onda do mesmo, fenômenos complementares podem ser medidos simultaneamente, indicando uma reinterpretação do princÃpio da complementaridade. O mesmo aparato também apresentou propriedades de apagador quântico. No segundo apresentamos um interferômetro de duas partÃculas e a maneira como a decoerência afeta o grau de interferência. Mostramos como os constituintes do ambiente, aqui considerados como fótons, podem destruir a oscilação na taxa de coincidência de detecção das partÃculas. Devido a sua caracterÃstica temporal, chamamos este processo de decoerência temporal quântica. No último trabalho estudamos a existência de uma nova famÃlia de soluções ortogonais da equação paraxial da luz. A amplitude complexa desses feixes são proporcionais à s funções hipergeométricas confluentes, que denominamos modos hipergeométricos do segundo tipo (HyG-II). Demonstramos formalmente que um meio com um perfil hiperbólico de Ãndice de refração pode gerar e suportar essa classe de feixes. Uma vez que esses modos são autofunções do momento angular orbital do fóton, concluÃmos que uma fibra ótica com este perfil de Ãndice, em certas situações, poderia levar vantagem em relação a outras fibras com Ãndice variável na capacidade de transmissão de dados
Theoretical study of the effect of hydrogen adsorption on the stability and electronic properties of hybrid monolayers
We have applied first-principle calculations, based on the density functional theory, to
analyze the stability, electronic and magnetic properties of monolayers of graphene with a
nanodomain of boron nitride (h-BN) with different geometries. To this end, we have
investigated the effects of the adsorption of one and two hydrogen atoms by different
atoms at the edge of the h-BN nanodomain, where we used the GGA approximation for the
functional exchange and correlation. Specifically, we found that the structures with
triangular-shaped nanodomains are the most stable and have a non-integer magnetic moment
upon adsorption of the hydrogen atoms. We have also shown that both the electronic and
magnetic properties can be influenced by the type of atom which adsorbs the hydrogen at
the edge of the nanodomain. Additionally, we have demonstrated that some structures can
quench the spin that would be generated by the adsorption of the hydrogen atoms
Greenberger–Horne–Zeilinger state generation with linear optical elements
We propose a scheme to probabilistically generate Greenberger–Horne–Zeilinger states encoded on the path degree of freedom of three photons. These photons are totally independent from each other, having no direct interaction during the whole evolution of the protocol, which remarkably requires only linear optical devices to work and two extra ancillary photons to mediate the correlation. The efficacy of the method, which has potential application in distributed quantum computation and multiparty quantum communication, is analyzed in comparison with similar proposals reported in the recent literature. We also discuss the main error sources that limit the efficiency of the protocol in a real experiment and some interesting aspects about the mediator photons in connection with the concept of spatial nonlocality