In this work we studied a system consisting of a pair of two-level trapped ions in coupled optics... more In this work we studied a system consisting of a pair of two-level trapped ions in coupled optics cavities, where we analyze the transfer of states of two qubits from the degrees of freedom (of movement and of internal states) of one ion to another. This system was studied near the blue side band frequency with a small gap. With analytical results obtained was possible to calculate the fidelity of transfer of entangled qubits.
ABSTRACT We compare two simple techniques for determination of equivalent-step-index parameters i... more ABSTRACT We compare two simple techniques for determination of equivalent-step-index parameters in single-mode fibres from measurement of the wavelength dependence of the far-field intensity profile. In one case the data is fitted directly by the step-index formula to yield the core radius and the v-value. In the other, wavelength dependence of the half-intensity angle is fitted to an empirical expression recently reported to give the core radius and the cutoff wavelength.
Neste trabalho analisamos a dinâmica das correlacoes quânticas em um sistema composto por dois os... more Neste trabalho analisamos a dinâmica das correlacoes quânticas em um sistema composto por dois osciladores harmonicos em contato com um mesmo reservatorio termico e acoplados entre si com um acoplamento dependente do tempo. O reservatorio termico modelado de acordo com o modelo de Caldeira-Leggett e tanto a abordagem via integrais de caminho quanto a abordagem via equacoes mestras sao usadas para estudar o sistema nos regimes Markoviano e nao-Markoviano. O Hamiltoniano que descreve o sistema e 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 correlacoes quânticas esta contida na matriz de covariância s. Conhecida a matriz s podemos medir o emaranhamento usando a negatividade Logaritmica e calcular uma aproximacao para a discordia quântica em estados Gaussianos, que e a discordia Gaussiana. Nos mostramos que mesmo a temperaturas muito altas as correlacoes quânticas, inclusive o emaranhamento, persistem. Esta persistencia tem uma relacao estreita com a estabilidade do sistema. Como as correlacoes quânticas sao a principal assinatura da mecânica quântica, isto sugere que este tipo particular de acoplamento entre os osciladores pode reduzir a descoerencia, introduzida pela interacao com o reservatorio termico Abstract
Uma Hamiltoniana simplificada e apresentada para a descricao de transicoes ferroeletricas. Gracas... more Uma Hamiltoniana simplificada e apresentada para a descricao de transicoes ferroeletricas. Gracas a aproximacao do campo molecular, a anarmonicidade do potencial local e tratada exatamente. Resultados interessantes sao obtidos para a importancia relativa dos efeitos quânticos na determinacao de Tc para o KDP, DKDP e Nitrito de Sodio. Uma curva e obtida para a influencia da barreira na determinacao de Tc. O modelo do poco quadrado simples descreve qualitativamente os resultados de Samara para a variacao da temperatura critica com a pressao hidrostatica, no KDP. Mostra-se que o modelo de Tsallis descreve quantitativamente os resultados de Samara para o KDP Abstract
We theoretically investigate how the initial state influence the entanglement dynamics between tw... more We theoretically investigate how the initial state influence the entanglement dynamics between two and three two-level atoms with dipole-dipole interaction (DDI) coupled to a whispering-gallery-mode (WGM) microtoroidal cavity. Two different cases, where the two atoms are coupled symmetrically or asymmetrically to the two WGMs through evanescent fields, are discussed in detail. Considering two types of initial states between the atoms and the symmetric regime, we show that for the initial entangled state, the sudden death and birth, as well as the freezing of the entanglement, can be obtained by adjusting both the scattering strength between the modes and the DDI, differently from the initial product state. Moreover, we note that the atomic entanglement generation is more susceptible to the scattering strength variation between the modes than to the DDI. In addition, for the asymmetric regime, the entanglement generation is strongly dependent on the atomic location and the scattering...
Um estudo da transicao de fase ferro eletrica em materiais da familia KDP e tambem no par PbHPO4-... more Um estudo da transicao de fase ferro eletrica em materiais da familia KDP e tambem no par PbHPO4-PbDPO4, focalizando tres quantidades fisicas, a saber, Temperatura Critica Tc, Polarizacao eletrica espontânea a zero Kelvin PM, e Constante de Curie Cc, proximo de Tc, e realizado, no quadro de uma Hamiltoniana simplificada. A referida Hamiltoniana contem, ao contrario da Hamiltoniana de De Gennes, um termo onde a energia cinetica entra de maneira explicita, um termo de potencial local simetrico anarmonico e um termo de muitos-corpos semelhante a interacao de Heisenberg. A analise toda e feita na Aproximacao do Campo Molecular, a qual juntamente com a forma do potencial local permitiram a inclusao de todos os niveis de energia da Hamiltoniana local, necessarios nos calculos estatisticos quânticos na determinacao das quantidades acima referidas. Resultados interessantes sao obtidos para a importância relativa dos efeitos quânticos na determinacao de Tc, PM e Cc para elementos da familia ...
1 INTRODUCTION The dynamics of a single mode CO=laser has been investigated by performing low fre... more 1 INTRODUCTION The dynamics of a single mode CO=laser has been investigated by performing low frequency modulation of either the cavity toss parameter or the pump parameter. Delayed bifurcations/l/ are observed only in the second case. This phenomenor. is related to a dynamic stabilization of the zero state intensity which becomes unstable for a pump value larger than the stationary value. In contrast, when we perform a linear sweep on the cavity loss parameter we 03serve a dynamical hysteresis depending on the modulation depth and on the sweep frequency but without time delay /2/. This difference between pump and loss modulation can be explained by considering a fourlevel molecular model which takes into account the coupling between the two active resonant levels of the P(20) transition and the other rotational levels of the vibrational bands (00'1 and 10'0) to which they belong /3/ .
One of the simplest ways of studying the interaction of the radiation with the matter is through ... more One of the simplest ways of studying the interaction of the radiation with the matter is through the Jaynes-Cummings model (JCM), that consists of an atom of two levels interacting with an electromagnetic field inside a cavity with high quality factor Q. This model has a great relevance in Quantum Optics, because it makes possible obtaining an exact analytical solution, within the dipole and rotate wave approximations (RWA). In the last years, several studies were realized on the system dynamics, where effects of collapses and revivals were observed in the inversion of atomic population, which proves the granular nature of the light and other associated nonclassical effects of the statistical properties of the field inside the cavity. With the help of the extensive literature on this topic, we verified that there is a model of nonlinear atomic homodyne detection, proposed by Wilkens and Meystre [1], that basically considers the JC molecule pumped by an intense coherent external fiel...
We present the cluster-type entangled coherent states (CTECS) and discuss their properties. A cav... more We present the cluster-type entangled coherent states (CTECS) and discuss their properties. A cavity QED generation scheme using suitable choices of atom-cavity interactions, obtained via detunings adjustments and the application of classical external fields, is also presented. After the realization of simple atomic measurements, CTECS representing nonlocal electromagnetic fields in separate cavities can be generated.
We investigate the entanglement dynamics of a system comprising a pair of two-level dipole-dipole... more We investigate the entanglement dynamics of a system comprising a pair of two-level dipole-dipole interacting atoms coupled to a microtoroidal resonator. Each atom is individually coupled with the two counter-propagating whispering gallery modes of the resonator through their evanescent fields. The atom-atom entanglement shown for several parameter sets of the system was obtained using the negativity. For ideal resonators, it is seen that the entanglement is correlated to the dipole-dipole interaction and the average number of photons when the modes of the resonator are prepared in a thermal state even at high temperatures. Further, for the non-ideal resonator case, where there is a small structural deformation of the microtoroidal structure that allows a direct coupling between the modes, a counter-intuitive result is presented. The imperfections also offer the advantage of generating maximally entangled states for a two-atom subsystem with maximum fidelity.
In this work we studied a system consisting of a pair of two-level trapped ions in coupled optics... more In this work we studied a system consisting of a pair of two-level trapped ions in coupled optics cavities, where we analyze the transfer of states of two qubits from the degrees of freedom (of movement and of internal states) of one ion to another. This system was studied near the blue side band frequency with a small gap. With analytical results obtained was possible to calculate the fidelity of transfer of entangled qubits.
ABSTRACT We compare two simple techniques for determination of equivalent-step-index parameters i... more ABSTRACT We compare two simple techniques for determination of equivalent-step-index parameters in single-mode fibres from measurement of the wavelength dependence of the far-field intensity profile. In one case the data is fitted directly by the step-index formula to yield the core radius and the v-value. In the other, wavelength dependence of the half-intensity angle is fitted to an empirical expression recently reported to give the core radius and the cutoff wavelength.
Neste trabalho analisamos a dinâmica das correlacoes quânticas em um sistema composto por dois os... more Neste trabalho analisamos a dinâmica das correlacoes quânticas em um sistema composto por dois osciladores harmonicos em contato com um mesmo reservatorio termico e acoplados entre si com um acoplamento dependente do tempo. O reservatorio termico modelado de acordo com o modelo de Caldeira-Leggett e tanto a abordagem via integrais de caminho quanto a abordagem via equacoes mestras sao usadas para estudar o sistema nos regimes Markoviano e nao-Markoviano. O Hamiltoniano que descreve o sistema e 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 correlacoes quânticas esta contida na matriz de covariância s. Conhecida a matriz s podemos medir o emaranhamento usando a negatividade Logaritmica e calcular uma aproximacao para a discordia quântica em estados Gaussianos, que e a discordia Gaussiana. Nos mostramos que mesmo a temperaturas muito altas as correlacoes quânticas, inclusive o emaranhamento, persistem. Esta persistencia tem uma relacao estreita com a estabilidade do sistema. Como as correlacoes quânticas sao a principal assinatura da mecânica quântica, isto sugere que este tipo particular de acoplamento entre os osciladores pode reduzir a descoerencia, introduzida pela interacao com o reservatorio termico Abstract
Uma Hamiltoniana simplificada e apresentada para a descricao de transicoes ferroeletricas. Gracas... more Uma Hamiltoniana simplificada e apresentada para a descricao de transicoes ferroeletricas. Gracas a aproximacao do campo molecular, a anarmonicidade do potencial local e tratada exatamente. Resultados interessantes sao obtidos para a importancia relativa dos efeitos quânticos na determinacao de Tc para o KDP, DKDP e Nitrito de Sodio. Uma curva e obtida para a influencia da barreira na determinacao de Tc. O modelo do poco quadrado simples descreve qualitativamente os resultados de Samara para a variacao da temperatura critica com a pressao hidrostatica, no KDP. Mostra-se que o modelo de Tsallis descreve quantitativamente os resultados de Samara para o KDP Abstract
We theoretically investigate how the initial state influence the entanglement dynamics between tw... more We theoretically investigate how the initial state influence the entanglement dynamics between two and three two-level atoms with dipole-dipole interaction (DDI) coupled to a whispering-gallery-mode (WGM) microtoroidal cavity. Two different cases, where the two atoms are coupled symmetrically or asymmetrically to the two WGMs through evanescent fields, are discussed in detail. Considering two types of initial states between the atoms and the symmetric regime, we show that for the initial entangled state, the sudden death and birth, as well as the freezing of the entanglement, can be obtained by adjusting both the scattering strength between the modes and the DDI, differently from the initial product state. Moreover, we note that the atomic entanglement generation is more susceptible to the scattering strength variation between the modes than to the DDI. In addition, for the asymmetric regime, the entanglement generation is strongly dependent on the atomic location and the scattering...
Um estudo da transicao de fase ferro eletrica em materiais da familia KDP e tambem no par PbHPO4-... more Um estudo da transicao de fase ferro eletrica em materiais da familia KDP e tambem no par PbHPO4-PbDPO4, focalizando tres quantidades fisicas, a saber, Temperatura Critica Tc, Polarizacao eletrica espontânea a zero Kelvin PM, e Constante de Curie Cc, proximo de Tc, e realizado, no quadro de uma Hamiltoniana simplificada. A referida Hamiltoniana contem, ao contrario da Hamiltoniana de De Gennes, um termo onde a energia cinetica entra de maneira explicita, um termo de potencial local simetrico anarmonico e um termo de muitos-corpos semelhante a interacao de Heisenberg. A analise toda e feita na Aproximacao do Campo Molecular, a qual juntamente com a forma do potencial local permitiram a inclusao de todos os niveis de energia da Hamiltoniana local, necessarios nos calculos estatisticos quânticos na determinacao das quantidades acima referidas. Resultados interessantes sao obtidos para a importância relativa dos efeitos quânticos na determinacao de Tc, PM e Cc para elementos da familia ...
1 INTRODUCTION The dynamics of a single mode CO=laser has been investigated by performing low fre... more 1 INTRODUCTION The dynamics of a single mode CO=laser has been investigated by performing low frequency modulation of either the cavity toss parameter or the pump parameter. Delayed bifurcations/l/ are observed only in the second case. This phenomenor. is related to a dynamic stabilization of the zero state intensity which becomes unstable for a pump value larger than the stationary value. In contrast, when we perform a linear sweep on the cavity loss parameter we 03serve a dynamical hysteresis depending on the modulation depth and on the sweep frequency but without time delay /2/. This difference between pump and loss modulation can be explained by considering a fourlevel molecular model which takes into account the coupling between the two active resonant levels of the P(20) transition and the other rotational levels of the vibrational bands (00'1 and 10'0) to which they belong /3/ .
One of the simplest ways of studying the interaction of the radiation with the matter is through ... more One of the simplest ways of studying the interaction of the radiation with the matter is through the Jaynes-Cummings model (JCM), that consists of an atom of two levels interacting with an electromagnetic field inside a cavity with high quality factor Q. This model has a great relevance in Quantum Optics, because it makes possible obtaining an exact analytical solution, within the dipole and rotate wave approximations (RWA). In the last years, several studies were realized on the system dynamics, where effects of collapses and revivals were observed in the inversion of atomic population, which proves the granular nature of the light and other associated nonclassical effects of the statistical properties of the field inside the cavity. With the help of the extensive literature on this topic, we verified that there is a model of nonlinear atomic homodyne detection, proposed by Wilkens and Meystre [1], that basically considers the JC molecule pumped by an intense coherent external fiel...
We present the cluster-type entangled coherent states (CTECS) and discuss their properties. A cav... more We present the cluster-type entangled coherent states (CTECS) and discuss their properties. A cavity QED generation scheme using suitable choices of atom-cavity interactions, obtained via detunings adjustments and the application of classical external fields, is also presented. After the realization of simple atomic measurements, CTECS representing nonlocal electromagnetic fields in separate cavities can be generated.
We investigate the entanglement dynamics of a system comprising a pair of two-level dipole-dipole... more We investigate the entanglement dynamics of a system comprising a pair of two-level dipole-dipole interacting atoms coupled to a microtoroidal resonator. Each atom is individually coupled with the two counter-propagating whispering gallery modes of the resonator through their evanescent fields. The atom-atom entanglement shown for several parameter sets of the system was obtained using the negativity. For ideal resonators, it is seen that the entanglement is correlated to the dipole-dipole interaction and the average number of photons when the modes of the resonator are prepared in a thermal state even at high temperatures. Further, for the non-ideal resonator case, where there is a small structural deformation of the microtoroidal structure that allows a direct coupling between the modes, a counter-intuitive result is presented. The imperfections also offer the advantage of generating maximally entangled states for a two-atom subsystem with maximum fidelity.
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Papers by José Roversi