arXiv subjects

Reinaldo de Melo e Souza

Publications and source records attributed to Reinaldo de Melo e Souza.

At least 19 recordsLinked to original sources

arXiv2026

Dynamical Casimir photons from rotation of a nonspherical particle

We consider a non-spherical neutral particle spinning in free space and interacting with the electromagnetic quantum vacuum. When the rotation axis is orthogonal to the particle symmetry axis, the scattered field develops frequency sidebands that induce the parametric emission of dynamical Casimir photon pairs. Under the structural constraint of a maximum tip velocity, the emission rate is maximized for a nearly spherical geometry and is further enhanced near a polaritonic resonance. For realistic material parameters, even these optimized upper bounds remain exceedingly small, setting stringent quantitative limits on free-space rotational dynamical Casimir emission with a single nanoparticle.

quant-ph↗

arXiv2026

The Dance of the Sheared Eigenfunctions

In this work, we delve into the theory of sheared potentials in non-relativistic quantum mechanics. After defining what we mean by a family of sheared potentials, we consider these families in two particular but emblematic cases, the harmonic oscillator and the symmetric potential well proportional to $|x|$. In both cases, besides determining the spectra, we analyse the impact of the shearing process on the respective eigenfunctions. The latter analysis is typically left aside in the literature, but here we show that the sheared eigenfunctions yield insights that allow for a deeper understanding of the main features exhibited by the spectra. Finally, we make a few comments about the connection between the change in the spectra of a given sheared family and the necessary work that must be made by an external agent to implement such a change.

quant-ph↗

arXiv2025

Enhancement of Electric Drive in Silicon Quantum Dots with Electric Quadrupole Spin Resonance

Quantum computation with electron spin qubits requires coherent and efficient manipulation of these spins, typically accomplished through the application of alternating magnetic or electric fields for electron spin resonance (ESR). In particular, electrical driving allows us to apply localized fields on the electrons, which benefits scale-up architectures. However, we have found that Electric Dipole Spin Resonance (EDSR) is insufficient for modeling the Rabi behavior in recent experimental studies. Therefore, we propose that the electron spin is being driven by a new method of electric spin qubit control which generalizes the spin dynamics by taking into account a quadrupolar contribution of the quantum dot: electric quadrupole spin resonance (EQSR). In this work, we explore the electric quadrupole driving of a quantum dot in silicon, specifically examining the cases of 5 and 13 electron occupancies.

cond-mat.mes-hall↗

arXiv2025

Influence of a Perfectly Conducting Plate on the Uehling Potential of QED

In this work, we investigate the influence of a perfectly conducting plate on the Uehling potential of Quantum Electrodynamics (QED), corresponding to the first loop correction to the classical Coulomb potential in that situation. We use the method of images adapted to the photon propagator, extending the method beyond the standard (classical) tree level calculation. We show that the effect of the plate on the quantum correction is much stronger than the expectation from a naive application of the method of images.

hep-th↗

arXiv2024

Dispersive interaction between two atoms in Proca Quantum Electrodynamics

We analyze the influence of a massive photon in the dispersive interaction between two atoms in their fundamental states. We work in the context of Proca Quantum Electrodynamics. The photon mass not only introduces a new length scale but also gives rise to a longitudinal polarization for the electromagnetic field. We obtain explicitly the interaction energy between the atoms for any distance regime and consider several particular cases. We show that, for a given interatomic distance, the greater the photon mass the better it is the non-retarded approximation.

hep-th↗

arXiv2022

Periodic strings: a mechanical analogy to photonic and phononic crystals

We study a periodic vibrating string composed of a finite sequence of string segments connected periodically, with each segment characterized by a constant linear mass density. The main purpose is to provide a configuration that can mimic the properties of photonic or phononic crystals and could be implemented in undergraduate physics laboratories. We demonstrate that this configuration displays frequency intervals for which wave propagation is not allowed (frequency bandgaps), in close analogy to photonic and phononic crystals. We discuss the behavior of these bandgaps when varying physical parameters, such as the values of the linear mass densities, the oscillation frequency, and the number of strings constituting the entire system. Some analogies with the propagation of electronic waves through a crystal lattice in condensed matter physics are also explored.

physics.class-ph↗

arXiv2022

Dynamical Casimir effects with atoms: from the emission of photon pairs to geometric phases

The coupling between a moving ground-state atom and the quantum electromagnetic field is at the origin of several intriguing phenomena ranging from the dynamical Casimir emission of photons to Sagnac-like geometric phase shifts in atom interferometers. Recent progress in this emerging field reveals unprecedented connections between non-trivial aspects of modern physics such as electrodynamic retardation, non-unitary evolution in open quantum systems, geometric phases, non-locality and inertia.

quant-ph↗

arXiv2022

Quantum Vacuum Sagnac Effect

We report on the quantum electrodynamical analogue of a Sagnac phase induced by the fast rotation of a neutral nanoparticle onto atomic waves propagating in its vicinity. The quantum vacuum Sagnac phase is a geometric Berry phase proportional to the angular velocity of rotation. The persistence of a noninertial effect into the inertial frame is also analogous to the Aharonov-Bohm effect. Here, a rotation confined to a restricted domain of space gives rise to an atomic phase even though the interferometer is at rest with respect to an inertial frame. By taking advantage of a plasmon resonance, we show that the magnitude of the induced phase can be close to the sensitivity limit of state of the art interferometers. The quantum vacuum Sagnac atomic phase is a geometric footprint of a dynamical Casimir-like effect

quant-ph↗

arXiv2021

Controlling the atom-sphere interaction with an external electric field

We investigate the system constituted by a polarizable atom near a nanosphere under the influence of an external electrostatic field, showing that the attractive dispersive force between them can be overcome by the electrostatic interaction. Therefore, in addition to the advantageous possibility of actively tuning the resultant force with an external agent without the requirement of physical contact, this force may also become repulsive. We analyze this situation in different physical regimes of distance and explore the interaction of different atoms with both metallic and dielectric spheres, discussing which cases are easier to control. Furthermore, our results reveal that these repulsive forces can be achieved with feasible field intensities in the laboratory.

quant-ph↗

arXiv2019

An Integrodifferential Equation for Electromagnetic Fields in Linear Dispersive Media

We extend the usual derivation of the wave equation from Maxwell's equations in vacuum to the case of electromagnetic fields in dispersive homogeneous isotropic linear media. Usually, dispersive properties of materials are studied in Fourier space. However, it can be rewarding to consider these properties as causal functions of time. Due to temporal non locality, this procedure gives rise to an integrodifferential equation for the electromagnetic fields, which we also call a wave equation. We have not found this equation in the literature and we show in this paper why it can be useful.

physics.class-ph↗

arXiv2019

Stokes-anti-Stokes correlated photon properties akin to photonic Cooper pairs

Photons interact with each other in condensed matter through the same mechanism that forms Cooper pairs in superconductors -- the exchange of virtual phonons [PRL 119, 193603 (2017)]. It is however unclear which consequences of this interaction will be observable and potentially lead to further analogy with superconductivity. We investigate the energy, momentum and production rate of correlate Stokes-anti-Stokes (SaS) photons in diamond and other transparent media, experiencing properties akin to those of electronic Cooper pairs. The rate of correlated SaS production depends on the energy shifts of the pair, which in the BCS theory determines whether there should be an attractive or repulsive interaction. With this view, we only observe correlated SaS in the case of attractive interactions. While traditional photon-phonon collisions scatter light in all directions, the correlated SaS photons follow the same path as the noninteracting laser. The observed correlated SaS photon pairs are rare, but our model indicates paths to achieve higher interaction energies.

quant-ph↗

arXiv2018

Repulsive van der Waals interaction between a quantum particle and a conducting toroid

We calculate the non-retarded dispersion force exerted on an electrically polarizable quantum particle by a perfectly conducting toroid, which is one of the most common objects exhibiting a non-trivial topology. We employ a convenient method developed by Eberlein and Zietal that essentially relates the quantum problem of calculating dispersion forces between a quantum particle and a perfectly conducting surface of arbitrary shape to a corresponding classical problem of electrostatics. Considering the quantum particle in the symmetry axis of the toroid, we use this method to find an exact analytical result for the van der Waals interaction between the quantum particle and the conducting toroid. Surprisingly, we show that for appropriate values of the two radii of the toroid the dispersive force on the quantum particle is repulsive. This is a remarkable result since repulsion in dispersive interactions involving only electric objects (and particles) in vacuum is rarely reported in the literature. Final comments are made about particular limiting cases as, for instance, the quantum particle-nanoring system.

quant-ph↗

arXiv2018

Microscopic dynamical Casimir effect

We consider an atom in its ground state undergoing a non-relativistic oscillation in free space. The interaction with the electromagnetic quantum vacuum leads to two effects to leading order in perturbation theory. When the mechanical frequency is larger than the atomic transition frequency, the dominant effect is the motion-induced transition to an excited state with the emission of a photon carrying the excess energy. We compute the angular distribution of emitted photons and the excitation rate. On the other hand, when the mechanical frequency is smaller than the transition frequency, the leading-order effect is the parametric emission of photon pairs, which constitutes the microscopic counterpart of the dynamical Casimir effect. We discuss the properties of the microscopic dynamical Casimir effect and build a connection with the photon production by an oscillating macroscopic metallic mirror.

quant-ph↗

arXiv2017

Photonic Counterparts of Cooper Pairs

The microscopic theory of superconductivity raised the disruptive idea that electrons couple through the elusive exchange of virtual phonons, overcoming the strong Coulomb repulsion to form Cooper pairs. Light is also known to interact with atomic vibrations, as for example in the Raman effect. We show that photon pairs exchange virtual vibrations in transparent media, leading to an effective photon-photon interaction identical to that for electrons in BCS theory of supercondutivity, in spite of the fact that photons are bosons. In this scenario, photons may exchange energy without matching a quantum of vibration of the medium. As a result, pair correlations for photons scattered away from the Raman resonances are expected to be enhanced. Experimental demonstration of this effect is provided here by time correlated Raman measurements in different media. The experimental data confirm our theoretical interpretation of a photonic Cooper pairing, without the need for any fitting parameters.

quant-ph↗

arXiv2016

Is the tautochrone curve unique?

The answer to this question is no. In fact, in addition to the solution first obtained by Christiaan Huygens in 1658, given by the cycloid, we show that there is an infinite number of tautochrone curves. With this goal, we start by briefly reviewing an the problem of finding out the possible potential energies that lead to periodic motions of a particle whose period is a given function of its mechanical energy. There are infinitely many solutions, called sheared potentials. As an interesting example, we show that a Pöschl-Teller and the one-dimensional Morse potentials are sheared relative to one another for negative energies, clarifying why they share the same periods of oscillations for their bounded solutions. We then consider periodic motions of a particle sliding without friction over a track around its minimum under the influence of an uniform gravitational field. After a brief historical survey of the tautochrone problem we show that, given the period of oscillations, there is an infinity of tracks which lead to the same periods. As a bonus, we show that there are infinitely many tautochrones.

physics.class-ph↗

arXiv2016

Decoherence by spontaneous emission: a single-atom analog of superradiance

We show that the stationary decoherence rate of an open quantum system can be decomposed as a sum of local and nonlocal contributions, respectively related to the strength of the coupling between system and environment, and to the quality of the information about the system leaking into the environment. Both terms arise naturally in the framework of the influence functional, with the nonlocal term arising from the coupling between the backward and forward histories describing the open quantum system time evolution. While the local contribution always yields a positive decoherence rate, the nonlocal one may lead to recoherence when only partial information about the system is obtained from the disturbed environment. We illustrate these concepts in the framework of interferometry with trapped atoms, by analyzing the effect of spontaneous emission on the coherence of the center-of-mass.

quant-ph↗

arXiv2015

Thinking anew causality problems for the radiation reaction force

In this work, we analyze a Lagrangian formalism recently proposed to approach the issue of the Abraham-Lorentz force. Instead of involving only position and velocity, as usual in Classical Mechanics, this Lagrangian involves the acceleration of the charge. We find the conserved momentum of the charge in the absence of any field and show that it contains an acceleration term. This enables us to re-visit the well-known pre-acceleration problem and show that, contrary to what has been widely believed, it is not related to any violation of causality.

hep-th↗

arXiv2015

The influence of a surface in the non-retarded interaction between two atoms

In this work we obtain analytical expressions for the non-additivity effects in the dispersive interaction between two atoms and perfectly conducting surface of arbitrary shape in the non-retarded regime. We show that this three bodies quantum-mechanical problem can be solved by mapping it into a two-bodies electrostatic one. We apply the general formulas developed in this paper in several examples. Firstly we re-derive the London interaction as a particular case of our formalism. Then we treat two atoms in the presence of a plane, re-obtained the result displayed in the literature. After we add some new examples. A particularly interesting one is two atoms inside a plate capacitor, a situation where non-additivity is very manifest since the plates lead to the exponentially suppression of the interaction of the atoms, provided the atoms are separated by a distance of the order of the distance between the plates or greater. Our results holds even in the presence of other atoms inside the plate capacitor. As a last example we deal with two atoms in the presence of a sphere, both grounded and isolated. We show that for realistic experimental parameters the non-additivity may be relevant for the force in each atom.

quant-ph↗