Brazilian Journal of Physics最新文献

Hybrid nanocomposites such as Graphene-TiO₂ (Titanium Dioxide) combine the outstanding electrical conductivity of graphene with the high dielectric constant and photocatalytic capabilities of TiO₂. This synergy leads to notable enhancements in the electromagnetic performance of radiator design. Graphene-ZnO hybrid nanocomposites merge the remarkable electrical properties of graphene with the advantageous dielectric and semiconducting characteristics of ZnO (Zinc Oxide), resulting in substantial enhancements in gain, radiation efficiency and bandwidth of radiator design. Hybrid nanocomposite coated stub is designed to support two distinct frequency bands, independently improving the electromagnetic radiation in both the lower and upper bands of the radiator. The hybrid nanocomposite material Graphene-TiO₂ enhance electromagnetic radiation of lower band of dual band radiator and the second hybrid nanocomposite (HN) material Graphene-ZnO for upper band. The radiator design has rectangular ring CPW ground plane, and two rectangular stub on left and right side of signal strip. The HN coated longer stub improve electromagnetic radiation of lower band (LB) and shorter stub for upper band (UB). HN coated radiators average value of bandwidth improved by 0.71 GHz and gain enhanced by 94% in LB and 131% UB as compared to radiator without HN material coating. The average radiation efficiency of proposed radiator is 91% but the traditional radiator is only 68% and covers 3.5 GHz WiMAX, 3.3–4.2 GHz 5G SUB − 6 GHz, 5G NR 78 band, lower and upper 6 GHz 5G bands.

We report the fabrication of highly sensitive and reproducible surface-enhanced Raman spectroscopy (SERS) substrates based on porous silicon (PSi) decorated with silver nanoparticles (AgNPs) using the Cathodic Cage Plasma Deposition (CCPD) technique. Unlike conventional sputtering or wet-chemical methods, CCPD enables uniform AgNP coverage across the porous network at low cost and with high deposition efficiency. The resulting PSi@AgNPs substrates exhibit a well-controlled pore morphology with homogeneous nanoparticle distribution, as confirmed by FEG-SEM and EDS analyses. Using Crystal Violet (CV) as a model analyte, the substrates achieve detection limits down to ~ 7 ppb and enhancement factors on the order of 10⁵, with relative standard deviations below 20% for most characteristic bands. These results demonstrate that CCPD provides a scalable and versatile route for engineering SERS-active nanostructures, bridging sensitivity, reproducibility, and manufacturing simplicity. Our findings highlight CCPD@PSi as a promising platform for low-cost and reliable SERS sensors in chemical, environmental, and biomedical applications.

We present a broadband type-II SPDC source operating near 800 nm, developed as a platform for quantum communication between sites in the city of Recife connected by kilometers of optical fibers. Local measurements of temporal correlations and Bell inequality violations confirm the generation of robust polarization-entangled photon pairs suitable for quantum key distribution (QKD). Coincidence measurements, where one photon of each pair is sent to remote nodes and returned via a fiber loop, show that quantum correlations are maintained despite propagation losses and chromatic dispersion. These results establish the capability of our system to support QKD protocols, such as BB84 and Ekert91, in metropolitan optical networks.

This study explores the synthesis, structural, and functional characterization of poly-crystalline ceramics 0.92BaTi_1 − xZr_xO₃−0.08K_0.73Bi_0.09NbO₃ (BT_1 − xZ_xO-KBN), focusing on the values of x = 0, 0.05, 0.10, and 0.15. These ceramics were prepared via a traditional solid-state process. The highly crystalline and single/mixed-phase structures were validated by X-ray diffraction (XRD) and Rietveld refinement. Surface morphology and compositional homogeneity were examined using high-resolution field-emission scanning electron microscopy (FESEM) and energy-dispersive X-ray analysis (EDXA). Additionally, analysis of grain size using Image J software revealed important connections between microstructure and material characteristics. The study also examined the impact of the frequency and temperature on the dielectric characteristics, to highlight the importance of both operating frequency and thermal stability in the design and application of dielectric materials. Polarization-electric field (P − E) hysteresis loops revealed impressive ferroelectric properties, including a maximum recoverable energy density of 104.41 mJ/cm³ (∼0.1 J/cm³) for x = 0.05, as well as remarkable energy efficiency of 90.95% for x = 0.15 at room temperature (RT) and 100 Hz. Furthermore, the materials demonstrated outstanding stability at temperatures ranging from 30 °C to 100 °C. These findings underscore the potential of these ceramics for many applications, particularly in energy storage and high-frequency electronic devices.

I carried out a study on the relationship between the squares of the charged Higgs boson Yukawa coupling constants associated with the charged Higgs boson, obtained in the context of the lepton-specific two Higgs doublet model (LS2HDM), starting from the fraction of new physics contributions to the total decay widths of leptonic tau decays. (tau ^{-} rightarrow mu ^{-} bar{nu }_mu nu _tau ) and (tau ^{-} rightarrow e^{-} bar{nu }_e nu _tau ). To do it, I calculate the total decay widths of these processes in the context of the LS2HDM by considering that these leptonic tau decays are mediated through the exchange of charged electroweak gauge boson and charged Higgs boson, in such a way that these widths depend on the charged Higgs boson mass and the ratio between the vacuum expectation values of the two Higgs doublets, which are unknown parameters. After expressing the ratio between the new-physics contributions to the total decay widths at one-loop order, I explicitly assume the scalar mass degeneracy limit given by (m_{A}=m_{H}=m_{H^{pm }}). In this specific limit, the one-loop contributions of all Higgs bosons are suppressed with respect to the tree-level terms. As a result, the previously unknown parameters cancel out, leading to a direct relation between the squares of the charged Higgs boson Yukawa coupling constants that enter the calculation of the total decay widths. This relation depends on the values of the elements of the leptonic flavor mixing matrix, which are numerically estimated by assuming that mass matrices have two-zero textures. To validate the relationship found, we perform a self-consistency analysis using an assumption of hierarchy in the mass spectrum, resulting in this relationship satisfying the same hierarchy but now between the Yukawa coupling constants.

As superconducting circuits emerge as a leading platform for scalable quantum information processing, building comprehensive bridges from the foundational principles of macroscopic quantum phenomena to the architecture of modern quantum devices is increasingly essential for introducing new researchers to the field. This tutorial provides a self-contained, pedagogical introduction to superconducting quantum circuits at the undergraduate level. Beginning with an overview of superconductivity and the Josephson effect, the tutorial systematically develops the quantization of microwave circuits into the framework of circuit quantum electrodynamics (cQED). The transmon qubit is then introduced as a state-of-the-art application, with a detailed derivation of its Hamiltonian and its interaction with control and readout circuitry. The theoretical formalism is consolidated through a numerical simulation of vacuum Rabi oscillations in a driven transmon-resonator system, a canonical experiment that demonstrates the coherent energy exchange characteristic of the strong coupling regime. This work serves as a foundational guide and first point of contact, equipping students and researchers with the conceptual and mathematical tools necessary to understand and engineer superconducting quantum hardware.

Conventional logic circuits are known as irreversible logic circuits as they release energy into the environment as a result of information loss. Reversible logic circuits have the ability to reduce garbage outputs, quantum costs, and power distribution. In recent years, researchers have embraced the use of all-optical reversible logic circuits for their research endeavours. In this work, a novel all-optical architecture of reversible Toffoli, Peres, Feynman, and double Feynman logic gates employing silicon microring resonator is presented. These gates are realized in MATLAB and finite difference time domain (FDTD)-based numerical simulation platform. The proposed reversible gates are particularly useful in different arithmetic and logic operations because of small size and fast speed. The assessment and analyze of several performance-indicating variables are carried out and the values are satisfactory for good design. Following the analysis, optimal parameters have been selected for practical implementation.

Comprehending the dynamics of dust acoustic modes and the ability to tune their effective parameters facilitates the optimization of plasma phenomena and structures, while also providing deeper insights into the underlying physics of oscillations involving massive charged grains. In this study, we investigate the influence of cathode potential on the evolution of dust ion acoustic (DIA) waves in a multicomponent dusty plasma containing a separate electron beam (e-beam). Our analysis reveals that cathode potential plays a crucial role in modulating the effect of the e-beam on DIA mode dynamics. Notably, at a specific cathode potential, denoted as (:{varphi:}_{CN}), the contribution of the e-beam to DIA wave propagation becomes negligible. Numerical results indicate that (:{varphi:}_{CN}) gradually increases with rising concentration of negatively charged grains, a trend that becomes more pronounced at elevated electron temperatures. Furthermore, in plasmas containing negatively charged grains, increasing the electron number density induces a nonlinear decrease in (:{varphi:}_{CN}), conversely, in plasmas with positively charged dust grains, the opposite trend is observed. Our findings offer an effective strategy for manipulating e-beam-induced modifications in DIA mode behavior.

This work surveys the historical and conceptual struggle between realism and anti-realism in quantum mechanics, focusing on the Einstein–Podolsky–Rosen (EPR) paradox, hidden-variable interpretations, and Bell’s inequalities. Beginning with the landmark critique by von Neumann on hidden variable theories and the revival of nonlocal determinism in Bohm’s pilot-wave model, the study examines Bell’s 1964 theorem, its challenge to local realism, and its later extension through GHZ states that establish deterministic contradictions without relying on inequalities. The review further addresses major experimental tests—photon-based, ion-trap, and hybrid platforms—that progressively closed key loopholes (detection, locality, freedom-of-choice, and coincidence-time). Despite the empirical demise of local hidden variables, de Broglie-Bohm’s theory and recent Planck-scale deterministic proposals (such as ’t Hooft’s) remain viable realist frameworks. In conclusion, although local realism appears incompatible with observed quantum phenomena, nonlocal realism remains a plausible interpretive stance, and the choice between emergent indeterminism and deeper deterministic structures remains unresolved.