Brazilian Journal of Physics最新文献

Superconducting quantum circuits are a leading platform for quantum-information processing, but their development requires expertise spanning device design, microfabrication, cryogenic operation, microwave control, and quantum characterization. In this work, we report the realization of a flux-tunable superconducting transmon platform and present an integrated workflow encompassing design, fabrication, measurement, and numerical modeling. The device consists of an (Al/AlO_x/Al) transmon coupled to a three-dimensional microwave cavity operating in the circuit quantum electrodynamics (cQED) dispersive regime. Two-tone spectroscopy reveals a fundamental transition frequency of (omega _{01}=5.0122~textrm{GHz}) and an anharmonicity of (alpha /2pi =-202.4~textrm{MHz}), corresponding to (E_J/E_C approx 82.9). Flux spectroscopy yields a cavity-qubit coupling strength of (g/2pi = 260~textrm{MHz}), while the cavity linewidth gives a loaded quality factor of (Q_L=6127) and a Purcell limit of (T_1^{textrm{Purcell}}approx 82~mu textrm{s}). Time-domain measurements yield coherence times of (T_1 = 17.4~mu textrm{s}) and (T_2^* = 5.8~mu textrm{s}). To investigate coherence and dissipation in the device, the experimental observations are analyzed within a Lindblad master-equation framework describing cavity photon loss and thermal excitation, qubit energy relaxation, and pure dephasing processes. Using a set of experimentally extracted parameters, the model reproduces the measured spectroscopic and time-domain observables, providing a quantitative description of the open-system dynamics of the transmon-cavity platform. The analysis shows that the measured coherence is primarily limited by pure dephasing and energy-relaxation processes, whereas thermal excitation plays a minor role under the experimental conditions. Inspired by the broader framework of quantum dissipation in macroscopic quantum systems pioneered by Caldeira and collaborators, this approach enables a quantitative analysis of relaxation and dephasing processes in superconducting quantum circuits. Beyond the characterization of a single device, the present work demonstrates the establishment of the expertise, infrastructure, and experimental workflow required for the design, fabrication, measurement, and modeling of superconducting quantum circuits, contributing to the development of quantum technologies in Brazil and related applications.

This study investigates the mechanical behavior of two-dimensional TH-graphyne nanosheets using molecular dynamics simulations. The pristine nanosheet exhibits significant mechanical anisotropy, with Young’s moduli of 204.77 GPa and 270.19 GPa and ultimate tensile strengths of 51.03 GPa and 92.73 GPa along the x- and y-directions, respectively. The influence of crack orientation (0°–90°) shows up to a 54.5% reduction in stiffness and a 75.6% drop in strength. Temperature increases from 200 K to 1000 K results in modulus reductions of over 65% and decreases fracture toughness (K_IC) by approximately 78%. Crack length variations from 30 Å to 60 Å lead to stiffness reductions of up to 71.7% and a drop in toughness by as much as 84.5%. The fracture process is characterized by brittle failure initiated at the crack tip, with minimal plastic deformation observed during propagation.

This paper presents a semirelativistic theoretical study of a laser-assisted inelastic electron-atom scattering. Specifically, we investigate the laser-assisted excitation of atomic hydrogen from the metastable 2s state to the 4s state, induced by electron impact with particular emphasis upon spin-dependent effects. The analysis is carried out within the framework of the first Born approximation, while the interaction of the incident and scattered electrons with the laser field is described using Dirac–Volkov states. An analytical expression for the spin-unpolarized differential cross section is derived, providing a reference for assessing the consistency and reliability of the adopted theoretical approach. In addition, the spin-flip and spin–non-flip differential cross sections are investigated. The numerical results show that the spin-flip contribution is negligible compared with the spin–non-flip contribution over the range of parameters considered, indicating that spin-conserving transitions dominate the excitation process.

This study is an extension of our experimental work on synthesis of WS₂ nanolayers; by varying laser energy in pulsed laser deposition, indicating sulfur deficient nanolayers. Hence, we further investigated the influence of number and different vacancy configurations within the non-periodic supercell, appearing to be at the edge or at the center, of sulfur vacancy (SV) and oxygen doping (OD), on the band structure, bandgap and density of states of the monolayers (ML) and bilayers (BL) of 2 H WS₂ polymorph, using Density functional theory. The (001) slab model of the WS₂ ML & BL was made with an array of 3 × 3 × 1 and 3 × 3 × 2 supercells, respectively. The number of SV & OD was varied from 1 to 3 and 1 to 2, respectively. For edge appearing SV WS₂ ML, the bandgap narrows rapidly with increase of SV and closes for 3 SV; having S/W ratio of 1.66. For center appearing SV, the bandgap also narrows slowly with increase of SV and remains slightly open for 3 SV. In WS₂ BL, the bandgap remains open for edge and center appearing 3 SV. The 1 O atom (5.55% doping) doped pristine ML, shows 0.5% to 1.99% bandgap opening, as compared to pristine ML. The 2 O atom (11.11%) doped pristine ML, shows 5.5% to 9.95% bandgap narrowing. This work indicates the feasibility of the bandgap engineering of WS₂ nanolayers by controlled SV and O doping.

This study investigates the elastic scattering of ⁷Be nuclei on ⁹Be, ²⁸Si, and ⁵⁸Ni targets at laboratory energies near the Coulomb barrier. The analysis was conducted using two complementary theoretical frameworks: the Optical Model (OM) and the Continuum-Discretized Coupled-Channels (CDCC) method. Within the OM, a microscopic bare potential was generated using the São Paulo potential to define both the real and imaginary nuclear components. Two fitting approaches were adopted: a one-parameter approach (SPP2-I) with the real part fixed at its theoretical value, and a two-parameter approach (SPP2-II) with both real and imaginary strengths allowed to vary. The CDCC approach explicitly incorporated the ³He + ⁴He cluster configuration of ⁷Be, allowing for couplings between the elastic channel and the breakup continuum. The research focuses on two unresolved questions: the potential manifestation of the breakup threshold anomaly in ⁷Be-induced reactions, and the magnitude of the continuum coupling effects on the elastic scattering observables.

Consider a bipartite quantum system (S=AB) such that each part interacts only with its local environment. Under such circumstances, one expects that the entanglement between parts A and B does not increase after the time evolution. In fact, this is the case if the reduced dynamics of the system is given by (mathcal {E}_{A}otimes mathcal {E}_{B}), where (mathcal {E}_{A}) and (mathcal {E}_{B}) are quantum channels, i.e., completely positive trace-preserving maps. But, the reduced dynamics of the system may be given by a map as (Psi _{A}otimes Psi _{B}), where (Psi _{A}) and (Psi _{B}) are local non-positive maps. Then, the entanglement between A and B can exceed its initial value, as was shown in the case studied by Jordan et al. [ Phys. Rev. A 76, 022102 (2007)]. In this paper, we first explore the general circumstances under which one can find such cases as they found. Next, we introduce another general procedure which leads to local non-positive maps that exhibit entanglement exceeding. Furthermore, we demonstrate that this apparent entanglement increase in the two above procedures corresponds physically to the retrieval of pre-existing inaccessible entanglement stored across the global system-environment degrees of freedom, rather than genuine generation of the entanglement ex nihilo.

Einstein-Born-Infeld is a charged black hole solution of general relativity with Born-Infeld nonlinear electrodynamics, which has interesting physical features. It violates Bekenstein’s entropy upper bound, and it can overcharge with respect to the Reissner-Nordström black hole. It presents an optimum situation to test the cosmic censorship conjecture, which is another important conjecture in black hole physics. In principle, this analysis requires the calculation of the self-energy of a test particle in the vicinity of the black hole, which, in general, is not feasible because of the electromagnetic nonlinearities. In this work, we propose an alternative approach that allows us to explore the whole parameter space of the Einstein-Born-Infeld black hole and test the validity of the cosmic censorship conjecture.

The reflectometry technique in NUR Research Reactor of Algeria was used for the measurement the neutron capture cross section for the ¹⁷⁶Lu(n,γ)¹⁷⁷Lu reaction at 3.626 meV energy. The Neutron Activation Analysis (NAA) technique using ¹⁹⁷Au(n,γ)¹⁹⁸Au as reference reaction was adopted. The. γ-ray spectra measurements were made for the Germanium Hyper Pure for the Lu₂O₃. This experiment is the first time at this energy. A resulting value of σ (3827 ± 191) b was measured for the neutron cross section after correction for neutron self-shielding and γ attenuation effects. The measured value was then compared to the evaluated cross sections reported in two different libraries of neutron databases ENDF/B-VIII.1 and JEFF-4.0. The extrapolated for the neutron capture cross section ¹⁷⁶Lu(n,γ)¹⁷⁷Lu reaction at 0.0253 eV was compared with evaluated and experimental data. A scarcity of experimental data at 0.0253 eV limits the possibility of conducting a comprehensive comparison with the available results.

Understanding the relaxation dynamics of isolated quantum systems remains a central challenge in nonequilibrium physics. In this short review, we discuss recent experimental and theoretical advances in universal dynamics of turbulent Bose gases, with particular emphasis on nonthermal fixed points and wave turbulence in our experimental system at the São Carlos Institute of Physics of the University of São Paulo. We highlight the emergence of self-similar scaling behavior and its connection to particle and energy transport across momentum scales. In addition, we discuss an approach in which a differential equation has a universal scaling solution, providing a practical framework for extracting universal exponents from limited regions of the momentum distribution. Furthermore, we recap experimental observations of direct and inverse cascades in a three–dimensional trapped Bose–Einstein condensate, revealing distinct relaxation stages governed by universal scaling laws. These results demonstrate that turbulence plays a key role in far–from–equilibrium dynamics, offering a unified perspective on transport processes and thermalization in quantum many–body systems.

The influence of resonances on the breakup dynamics of the ({^6})Li+(^{58})Ni and ({^6})Li+(^{208})Pb systems is investigated using the continuum discretized coupled-channels (CDCC) method at incident energies above the Coulomb barrier. The calculated elastic scattering angular distributions are found to reproduce the available experimental data for both systems. The effects of resonances on the total, Coulomb, and nuclear breakup cross sections are analyzed as functions of scattering angle and incident energy. For the ({^6})Li+(^{58})Ni system, non-resonant breakup contributions dominate the nuclear and total breakup cross sections, while resonance effects remain relatively weak. In contrast, resonant breakup cross section plays a significant role in the ({^6})Li+(^{208})Pb reaction, particularly in the Coulomb breakup cross section. The results show that the influence of resonances decreases with increasing incident energy, indicating the growing importance of non-resonant continuum couplings at higher energies. The dependence of breakup observables on dipole, quadrupole, and octupole couplings is also investigated, revealing a pronounced sensitivity to the multipolarity of the coupling. These findings demonstrate that the importance of resonant and non-resonant breakup mechanisms depends strongly on the target mass and incident energy.