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Papers by Wandearley Dias
We present the construction of a system that allows remote access and didatic control of a physic... more We present the construction of a system that allows remote access and didatic control of a physics experiment through the internet. More specifically, we describe a remote instrumentation system to determine of the value of the elementary charge by using the Millikan method. The system is composed of hardware and software integrated to an Arduino platform in order to control and communication with the computer. The evaluation of the prototype was conducted in two tests, involving a teacher from the public high school and 14 students also from the public high school. The quantitative and qualitative results point out to the feasibility of implementing the didatic resource.
Revista Brasileira de Ensino de Física, 2019
Resumo Apresentamos a elaboração de um sistema que permite o acesso remoto e controle didático de... more Resumo Apresentamos a elaboração de um sistema que permite o acesso remoto e controle didático de um experimento de física através da internet. Mais especificamente, descrevemos um sistema de instrumentação remota para determinação do valor da carga elementar através do método de Millikan. O sistema é constituído de elementos físicos (hardware) e lógicos (software) integrados à uma plataforma Arduino para o controle e interfaceamento com o computador. A avaliação do protótipo foi realizada em dois testes, envolvendo um professor da rede pública de ensino médio e 14 alunos também da rede pública de ensino médio. Os resultados quantitativos e qualitativos apontam para a viabilidade de implementação do recurso didático.
Physical Review B, 2007
We study numerically the effect of the on-site Hubbard interaction U on the dynamics of two elect... more We study numerically the effect of the on-site Hubbard interaction U on the dynamics of two electrons subjected to an external electric field and restricted to move in a linear chain with open boundaries. We solve the time-dependent Schrödinger equation to follow the time evolution of an initially localized two-electron state. For electrons initially far apart, the wave packet develops Bloch oscillations whose characteristic frequency is in agreement with a semiclassical calculation. For initially close electrons in a singlet state, a frequency doubling sets up, which is more pronounced for intermediate couplings. We discuss this effect by revealing the opposite trends the electron-electron coupling produces on the wave-packet components corresponding to bounded and unbounded states.
Physical Review B, 2010
We investigate the influence of the on-site Hubbard interaction U on the eigenstates and dynamics... more We investigate the influence of the on-site Hubbard interaction U on the eigenstates and dynamics of two electrons restricted to move in a linear chain with long-range correlated disorder. We solve the time-dependent Schrödinger equation to follow the time evolution of an initially localized Gaussian two-electron wave packet. In the regime of strongly correlated disorder, for which one-electron extended eigenstates emerge near the band center, the electron-electron coupling promotes the trapping of a finite portion of the wave packet. In the presence of a uniform electric field, the wave packet develops complex Bloch oscillations. The power spectrum of the centroid's velocity trace shows a splitting near the typical semiclassical Bloch frequency, as well as a frequency doubling phenomenon for intermediate couplings which is related to the bounded states components that are present in the wave packet. Finally, we show that localized and extended two-electron eigenstates coexist near the band center with the level spacing distribution showing a universal Poissonian form irrespective to the Hubbard coupling.
Physical Review A, 2021
The sensitivity of quantum systems to external disturbances is a fundamental problem for the impl... more The sensitivity of quantum systems to external disturbances is a fundamental problem for the implementation of functional quantum devices, quantum information and computation. Based on remarkable experimental progress in optics and ultra-cold gases, we study the consequences of a short-time (instantaneous) noise while an intensity-dependent phase acquisition is associated with a qubit propagating on N-cycle. By employing quantum coherence measures, we report emerging unstable regimes in which hitherto unknown quantum walks arise, such as self-focusing and breathing dynamics. Our results unveil appropriate settings which favor the stable regime, with the asymptotic distribution surviving for weak nonlinearities and disappearing in the thermodynamic limit with 1/N. The diagram showing the threshold between different regimes reveals the quantum gates close to Pauli-Z as more noise-tolerant. As we move towards the Pauli-X quantum gate, such aptness dramatically decreases and the threshold to self-focusing regime becomes almost unavoidable. Quantum gates close to Hadamard exhibit an unusual aspect, in which an increment of the nonlinear strength can remove the dynamics from self-focusing regime.
Physica A: Statistical Mechanics and its Applications, 2014
h i g h l i g h t s • We show a non monotonic behavior of the Anderson localization phenomenon. •... more h i g h l i g h t s • We show a non monotonic behavior of the Anderson localization phenomenon. • This behavior is associated with interaction between electrons. • We show such non-monotonic behavior is consistent with some many-body calculations.
Physics Letters A, 2010
We study the Anderson localization in two-dimensional lattices with long-range correlated hopping... more We study the Anderson localization in two-dimensional lattices with long-range correlated hopping terms. The hopping energies along one lattice direction will be generated by a superposition of uncorrelated and long-range correlated contributions. Our numerical results strongly suggest the presence of a Kosterlitz-Thouless-like transition above a critical correlation degree.
Physics Letters A, 2010
We study the effects of a Hubbard-like interaction on the dynamics of two electrons restricted to... more We study the effects of a Hubbard-like interaction on the dynamics of two electrons restricted to move in a linear chain. Our calculations suggest that the presence of bounded two-electron states in the initial Gaussian wave-packet plays significative roles on both unbiased and the electric-field biased wave-packet dynamics.
Physical Review B, 2010
ABSTRACT We offer a comparative study of the self-trapping phenomenon in square and honeycomb lat... more ABSTRACT We offer a comparative study of the self-trapping phenomenon in square and honeycomb lattices, showing its dependence on the initial condition and lattice topology. In order to describe the dynamical behavior of one-electron wave packets, we use a discrete nonlinear Schrödinger equation which effectively takes into account the electron-phonon interaction in the limit of an adiabatic coupling. For narrow wave packets and strong nonlinearities, the electron distribution becomes trapped irrespective to the lattice geometry. In the opposite regime of wide wave packets and small nonlinearities, a delocalized regime takes place. There is an intermediate regime for which self-trapping is attained in the honeycomb lattice while the wave packet remains delocalized in square lattices. Further, we show that the critical nonlinear strength χc scales linearly with the initial wave-packet participation function P(0) with the ratio χc/P(0) being on the order of the energy bandwidth.
Physica A: Statistical Mechanics and its Applications, 2014
We study the wavepacket dynamics of two interacting particles under an aperiodic potential that c... more We study the wavepacket dynamics of two interacting particles under an aperiodic potential that can be continuously tuned from a pseudo-random to a uniform regime. Assuming an on-site Hubbard interaction, we show that the influence of interaction is not strong enough to change the characteristic aperiodicity that signals the emergence of extended states. However, we unveil that the inter-particles interaction promotes a weakening of Anderson localization that is more prominent at intermediate couplings. The wavepacket dynamics in the regime presenting extended eigenstates show an oscillatory motion of the centroid while the wavepacket widens. We explain in detail the origin of these oscillations and discuss the characteristics of the Bloch oscillations of the two-particles wavepacket by exploring the relevance of bounded states to the dynamics of pair formation.
Journal of Magnetism and Magnetic Materials, 2009
We consider the one-dimensional quantum disordered S ¼ 1 2 Heisenberg ferromagnetic chain model w... more We consider the one-dimensional quantum disordered S ¼ 1 2 Heisenberg ferromagnetic chain model with long-range correlated exchange couplings and study the nature of collective two-spin excitations. By using an exact diagonalization of the Hamiltonian in the two-spin flip subspace, we compute the spin wave participation number to characterize the localized or delocalized nature of the two-magnon states. For strongly correlated random exchange couplings, extended two-spin excitations with finite energy appear. Integrating the time-dependent Schroedinger equation, we follow the time-evolution of an initially localized two-spin state. We find that, associated with the emergence of extended spin waves, the wave-packet mean-square displacement develops a ballistic spread. Further, the single-spin wave-packet acquires an asymmetric profile due to the kinematic interaction between the excited spins.
The European Physical Journal B, 2012
Considering the nonlinearity arising from the interaction between electrons and lattice vibration... more Considering the nonlinearity arising from the interaction between electrons and lattice vibrations, an effective electronic model with a self-interaction cubic term is employed to study the interplay between electron-electron and electron-phonon interactions. Based on numerical solutions of the timedependent nonlinear Schroedinger equation for an initially localized two-electron singlet state, we show that the magnitude of the electron-phonon coupling χ necessary to promote the self-trapping of the electronic wave packet decreases as a function of the electron-electron interaction U. We show that such dependence is directly linked to the narrowing of the band of bounded two-electron states as U increases. We obtain the transition line in the χ × U parameter space separating the phases of self-trapped and delocalized electronic wave packets. The present results indicates that nonlinear contributions plays a relevant role in the electronic wave packet dynamics, particularly in the regime of strongly correlated electrons.
We study the effects of a Hubbard-like interaction on the dynamics of two electrons restricted to... more We study the effects of a Hubbard-like interaction on the dynamics of two electrons restricted to move in a linear chain. Our calculations suggest that the presence of bounded two-electron states in the initial Gaussian wave-packet plays significative roles on both unbiased and the electric-field biased wave-packet dynamics.
We present the construction of a system that allows remote access and didatic control of a physic... more We present the construction of a system that allows remote access and didatic control of a physics experiment through the internet. More specifically, we describe a remote instrumentation system to determine of the value of the elementary charge by using the Millikan method. The system is composed of hardware and software integrated to an Arduino platform in order to control and communication with the computer. The evaluation of the prototype was conducted in two tests, involving a teacher from the public high school and 14 students also from the public high school. The quantitative and qualitative results point out to the feasibility of implementing the didatic resource.
Revista Brasileira de Ensino de Física, 2019
Resumo Apresentamos a elaboração de um sistema que permite o acesso remoto e controle didático de... more Resumo Apresentamos a elaboração de um sistema que permite o acesso remoto e controle didático de um experimento de física através da internet. Mais especificamente, descrevemos um sistema de instrumentação remota para determinação do valor da carga elementar através do método de Millikan. O sistema é constituído de elementos físicos (hardware) e lógicos (software) integrados à uma plataforma Arduino para o controle e interfaceamento com o computador. A avaliação do protótipo foi realizada em dois testes, envolvendo um professor da rede pública de ensino médio e 14 alunos também da rede pública de ensino médio. Os resultados quantitativos e qualitativos apontam para a viabilidade de implementação do recurso didático.
Physical Review B, 2007
We study numerically the effect of the on-site Hubbard interaction U on the dynamics of two elect... more We study numerically the effect of the on-site Hubbard interaction U on the dynamics of two electrons subjected to an external electric field and restricted to move in a linear chain with open boundaries. We solve the time-dependent Schrödinger equation to follow the time evolution of an initially localized two-electron state. For electrons initially far apart, the wave packet develops Bloch oscillations whose characteristic frequency is in agreement with a semiclassical calculation. For initially close electrons in a singlet state, a frequency doubling sets up, which is more pronounced for intermediate couplings. We discuss this effect by revealing the opposite trends the electron-electron coupling produces on the wave-packet components corresponding to bounded and unbounded states.
Physical Review B, 2010
We investigate the influence of the on-site Hubbard interaction U on the eigenstates and dynamics... more We investigate the influence of the on-site Hubbard interaction U on the eigenstates and dynamics of two electrons restricted to move in a linear chain with long-range correlated disorder. We solve the time-dependent Schrödinger equation to follow the time evolution of an initially localized Gaussian two-electron wave packet. In the regime of strongly correlated disorder, for which one-electron extended eigenstates emerge near the band center, the electron-electron coupling promotes the trapping of a finite portion of the wave packet. In the presence of a uniform electric field, the wave packet develops complex Bloch oscillations. The power spectrum of the centroid's velocity trace shows a splitting near the typical semiclassical Bloch frequency, as well as a frequency doubling phenomenon for intermediate couplings which is related to the bounded states components that are present in the wave packet. Finally, we show that localized and extended two-electron eigenstates coexist near the band center with the level spacing distribution showing a universal Poissonian form irrespective to the Hubbard coupling.
Physical Review A, 2021
The sensitivity of quantum systems to external disturbances is a fundamental problem for the impl... more The sensitivity of quantum systems to external disturbances is a fundamental problem for the implementation of functional quantum devices, quantum information and computation. Based on remarkable experimental progress in optics and ultra-cold gases, we study the consequences of a short-time (instantaneous) noise while an intensity-dependent phase acquisition is associated with a qubit propagating on N-cycle. By employing quantum coherence measures, we report emerging unstable regimes in which hitherto unknown quantum walks arise, such as self-focusing and breathing dynamics. Our results unveil appropriate settings which favor the stable regime, with the asymptotic distribution surviving for weak nonlinearities and disappearing in the thermodynamic limit with 1/N. The diagram showing the threshold between different regimes reveals the quantum gates close to Pauli-Z as more noise-tolerant. As we move towards the Pauli-X quantum gate, such aptness dramatically decreases and the threshold to self-focusing regime becomes almost unavoidable. Quantum gates close to Hadamard exhibit an unusual aspect, in which an increment of the nonlinear strength can remove the dynamics from self-focusing regime.
Physica A: Statistical Mechanics and its Applications, 2014
h i g h l i g h t s • We show a non monotonic behavior of the Anderson localization phenomenon. •... more h i g h l i g h t s • We show a non monotonic behavior of the Anderson localization phenomenon. • This behavior is associated with interaction between electrons. • We show such non-monotonic behavior is consistent with some many-body calculations.
Physics Letters A, 2010
We study the Anderson localization in two-dimensional lattices with long-range correlated hopping... more We study the Anderson localization in two-dimensional lattices with long-range correlated hopping terms. The hopping energies along one lattice direction will be generated by a superposition of uncorrelated and long-range correlated contributions. Our numerical results strongly suggest the presence of a Kosterlitz-Thouless-like transition above a critical correlation degree.
Physics Letters A, 2010
We study the effects of a Hubbard-like interaction on the dynamics of two electrons restricted to... more We study the effects of a Hubbard-like interaction on the dynamics of two electrons restricted to move in a linear chain. Our calculations suggest that the presence of bounded two-electron states in the initial Gaussian wave-packet plays significative roles on both unbiased and the electric-field biased wave-packet dynamics.
Physical Review B, 2010
ABSTRACT We offer a comparative study of the self-trapping phenomenon in square and honeycomb lat... more ABSTRACT We offer a comparative study of the self-trapping phenomenon in square and honeycomb lattices, showing its dependence on the initial condition and lattice topology. In order to describe the dynamical behavior of one-electron wave packets, we use a discrete nonlinear Schrödinger equation which effectively takes into account the electron-phonon interaction in the limit of an adiabatic coupling. For narrow wave packets and strong nonlinearities, the electron distribution becomes trapped irrespective to the lattice geometry. In the opposite regime of wide wave packets and small nonlinearities, a delocalized regime takes place. There is an intermediate regime for which self-trapping is attained in the honeycomb lattice while the wave packet remains delocalized in square lattices. Further, we show that the critical nonlinear strength χc scales linearly with the initial wave-packet participation function P(0) with the ratio χc/P(0) being on the order of the energy bandwidth.
Physica A: Statistical Mechanics and its Applications, 2014
We study the wavepacket dynamics of two interacting particles under an aperiodic potential that c... more We study the wavepacket dynamics of two interacting particles under an aperiodic potential that can be continuously tuned from a pseudo-random to a uniform regime. Assuming an on-site Hubbard interaction, we show that the influence of interaction is not strong enough to change the characteristic aperiodicity that signals the emergence of extended states. However, we unveil that the inter-particles interaction promotes a weakening of Anderson localization that is more prominent at intermediate couplings. The wavepacket dynamics in the regime presenting extended eigenstates show an oscillatory motion of the centroid while the wavepacket widens. We explain in detail the origin of these oscillations and discuss the characteristics of the Bloch oscillations of the two-particles wavepacket by exploring the relevance of bounded states to the dynamics of pair formation.
Journal of Magnetism and Magnetic Materials, 2009
We consider the one-dimensional quantum disordered S ¼ 1 2 Heisenberg ferromagnetic chain model w... more We consider the one-dimensional quantum disordered S ¼ 1 2 Heisenberg ferromagnetic chain model with long-range correlated exchange couplings and study the nature of collective two-spin excitations. By using an exact diagonalization of the Hamiltonian in the two-spin flip subspace, we compute the spin wave participation number to characterize the localized or delocalized nature of the two-magnon states. For strongly correlated random exchange couplings, extended two-spin excitations with finite energy appear. Integrating the time-dependent Schroedinger equation, we follow the time-evolution of an initially localized two-spin state. We find that, associated with the emergence of extended spin waves, the wave-packet mean-square displacement develops a ballistic spread. Further, the single-spin wave-packet acquires an asymmetric profile due to the kinematic interaction between the excited spins.
The European Physical Journal B, 2012
Considering the nonlinearity arising from the interaction between electrons and lattice vibration... more Considering the nonlinearity arising from the interaction between electrons and lattice vibrations, an effective electronic model with a self-interaction cubic term is employed to study the interplay between electron-electron and electron-phonon interactions. Based on numerical solutions of the timedependent nonlinear Schroedinger equation for an initially localized two-electron singlet state, we show that the magnitude of the electron-phonon coupling χ necessary to promote the self-trapping of the electronic wave packet decreases as a function of the electron-electron interaction U. We show that such dependence is directly linked to the narrowing of the band of bounded two-electron states as U increases. We obtain the transition line in the χ × U parameter space separating the phases of self-trapped and delocalized electronic wave packets. The present results indicates that nonlinear contributions plays a relevant role in the electronic wave packet dynamics, particularly in the regime of strongly correlated electrons.
We study the effects of a Hubbard-like interaction on the dynamics of two electrons restricted to... more We study the effects of a Hubbard-like interaction on the dynamics of two electrons restricted to move in a linear chain. Our calculations suggest that the presence of bounded two-electron states in the initial Gaussian wave-packet plays significative roles on both unbiased and the electric-field biased wave-packet dynamics.