arXiv subjects

Márcio M. Cunha

Publications and source records attributed to Márcio M. Cunha.

12 recordsLinked to original sources

arXiv2023

Approximate analytical solutions of the Schrödinger equation with Hulthén potential in the global monopole spacetime

In this paper, we study the nonrelativistic quantum mechanics of an electron in a spacetime containing a topological defect. We also consider that the electron is influenced by the Hulthén potential. In particular, we deal with the Schrödinger equation in the presence of a global monopole. We obtain approximate solutions for the problem, determine the scattering phase shift and the $S$-matrix, and analyze bound states.

quant-ph↗

arXiv2021

Effects of rotation and Coulomb type potential on the spin-1/2 Aharonov-Bohm problem

In this work, we investigate how both rotation and a Coulomb potential affect the quantum mechanical description of a spin-$1/2$ particle in the presence of the Aharonov-Bohm effect. We employ the method of the self-adjoint extensions in the framework of the Pauli-Schrödinger equation. We discuss the role of the spin degree of freedom on this problem, find the energy spectrum, and investigate the results in detail.

quant-ph↗

arXiv2020

On the Dirac oscillator in a spinning cosmic string spacetime in external magnetic fields: Investigation of energy spectrum and connection with the condensed matter physics

In this article, we study topological and noninertial effects on the motion of the two-dimensional Dirac oscillator in the presence of a uniform magnetic field and the Aharonov-Bohm potential. We obtain the Dirac equation that describes the model. Expressions for the wave functions and energy spectrum are derived. The energy spectrum of the oscillator as a function of the various physical parameters involved in the problem is rigorously studied. Finally, we present some analogies between our results and others of the condensed matter physics.

hep-th↗

arXiv2020

Tripartite entanglement: Foundations and applications

We review some current ideas about tripartite entanglement, the case representing the next level of complexity beyond the simplest one (though far from trivial), namely the bipartite. This kind of entanglement has an essential role in the understanding of foundations of quantum mechanics. Also, it allows several applications in the fields of quantum information processing and quantum computing. In this paper, we make a revision about the main foundational aspects of tripartite entanglement and we discuss the possibility of using it as a resource to execute quantum protocols. We present some examples of quantum protocols in detail.

quant-ph↗

arXiv2020

Relativistic quantum motion of an electron in spinning cosmic string spacetime in the presence of uniform magnetic field and Aharonov-Bohm potential

In this manuscript, we study the relativistic quantum mechanics of an electron in external fields in the spinning cosmic string spacetime. We obtain the Dirac equation, write the first and second-order equations from it, and then we solve these equations for bound states. We show that there are bound states solutions for the first-order equation Dirac. For the second-order equation, we show that its wave functions are given in terms of the Kummer functions and we determine the energies of the particle. We examine the behavior of the energies as a function of the physical parameters of the model, such as rotation, curvature, magnetic field, Aharonov-Bohm flux, and quantum numbers. Our study reveals that both curvature and rotation influence more intensely when these parameters have values smaller than 0.3. We also find that, depending on the values of these parameters, there are energy nonpermissible levels.

hep-th↗

arXiv2020

Quantum particle motion on the surface of a helicoid in the presence of harmonic oscillator

The geometric potential in quantum mechanics has been attracted attention recently, providing a formalism to investigate the influence of curvature in the context of low-dimensional systems. In this paper, we study the consequences of a helicoidal geometry in the Schrödinger equation dealing with an anisotropic mass tensor. In particular, we solve the problem of an harmonic oscillator in this scenario. We determine the eigenfunctions in terms of Confluent Heun Functions and compute the respective energy levels. The system exhibit several different behaviors, depending on the adjustment on the mass components.

quant-ph↗

arXiv2020

Spin current generation and control in carbon nanotubes by combining rotation and magnetic field

We study the quantum dynamics of ballistic electrons in rotating carbon nanotubes in the presence of a uniform magnetic field. When the field is parallel to the nanotube axis, the rotation-induced electric field brings about the spin-orbit interaction which, together with the kinetic, inertial, and Zeeman terms, compose the Schrödinger-Pauli Hamiltonian of the system. Full diagonalization of this Hamiltonian yields the eigenstates and eigenenergies leading to the calculation of the charge and spin currents. Our main result is the demonstration that, by suitably combining the applied magnetic field intensity and rotation speed, one can tune one of the currents to zero while keeping the other one finite, giving rise to a spin current generator.

cond-mat.mes-hall↗

arXiv2019

Influence of rotation on the electronic states, magnetization and persistent current in 1D quantum ring

Inertial effects can affect several properties of physical systems. In particular, in the context of quantum mechanics, such effects have been studied in diverse contexts. In this paper, starting from the Schrödinger equation for a rotating frame, we describe the influence of rotation on the energy levels of a quantum particle constrained to a one-dimensional ring in the presence of a uniform magnetic field. We also investigate how the persistent current and the magnetization in the ring are influenced by temperature and rotating effects.

quant-ph↗

arXiv2018

Finite-time collapse process and non-local correlations are incompatible with non-signaling theories

We propose a hidden variable analysis of collapse dynamics in which the state's reduction process may take a finite time $δt$. A full characterization of the model is given for the case of black boxes. By introducing nonlocal perfect correlations to a two black-boxes scenario, it is shown that in order to avoid faster than light communication, the reduction time associated to the system must be strictly null. Furthermore we prove that the result above holds even when there is a time window between the choice of both part's inputs. Our results represent a new evidence of the instantaneous nature of the wave function collapse process which could have implications in foundations of quantum mechanics and information science.

quant-ph↗

arXiv2018

Using three-partite GHZ states for partial quantum error-detection in entanglement-based protocols

The problem of noise incidence on qubits taking part of bipartite entanglement-based protocols is addressed. It is shown that the use of a three-partite GHZ state and measurements instead of their EPR counterparts allows the experimenter to detect $2/3$ of the times whenever one of the qubits involved in the measurement is affected by bit-flip noise through the mere observation of unexpected outcomes in the teleportation and superdense coding protocols when compared to the ideal case. It is shown that the use of post-selection after the detection of noise leads to an enhancement in the efficiency of the protocols. The idea is extended to any protocol using entangled states and measurements. Furthermore it is provided a generalization in which GHZ states and measurements with an arbitrary amount of qubits are used instead of EPR pairs, and remarkably, it is concluded that the optimal number of qubits is only three.

quant-ph↗

arXiv2016

Non-ideal teleportation of tripartite entanglement: Einstein-Podolsky-Rosen versus Greenberger-Horne-Zeilinger schemes

Channels composed by Einstein-Podolsky-Rosen (EPR) pairs are capable of teleporting arbitrary multipartite states. The question arises whether EPR channels are also optimal against imperfections. In particular, the teleportation of Greenberger-Horne-Zeilinger states (GHZ) requires three EPR states as the channel and full measurements in the Bell basis. We show that, by using two GHZ states as the channel, it is possible to transport any unknown three-qubit state of the form $c_0|000\rangle+c_1|111\rangle$. The teleportation is made through measurements in the GHZ basis, and, to obtain deterministic results, in most of the investigated scenarios, four out of the eight elements of the basis need to be unambiguously distinguished. Most importantly, we show that when both, systematic errors and noise are considered, the fidelity of the teleportation protocol is higher when a GHZ channel is used in comparison to that of a channel composed by EPR pairs.

quant-ph↗

arXiv2016

Remote preparation of $W$ states from imperfect bipartite sources

Several proposals to produce {\it tripartite} $W$-type entanglement are probabilistic even if no imperfections are considered in the processes. We provide a deterministic way to remotely create $W$ states out of an EPR source. The proposal is made viable through measurements (which can be demolitive) in an appropriate three-qubit basis. The protocol becomes probabilistic only when source flaws are considered. It turns out that, even in this situation, it is robust against imperfections in two senses: (i) It is possible, after postselection, to create a pure ensemble of $W$ states out of an EPR source containing a systematic error; (ii) If no postselection is done, the resulting mixed state has a fidelity, with respect to a pure $|W\rangle$, which is higher than that of the imperfect source in comparison to an ideal EPR source. This simultaneously amounts to entanglement concentration and {\it lifting}.

quant-ph↗