Brazilian Journal of Physics最新文献

These notes review a description of quantum mechanics in terms of the topology of spaces, basing on the axioms of Topological Quantum Field Theory and path integral formalism. In this description quantum states and operators are encoded by the topology of spaces that are used as modules to build the quantum mechanical model, while expectation values and probabilities are given by topological invariants of spaces, knots and links. The notes focus on the specific way the topology encodes quantum mechanical features, or, equivalently, on how these features can be controlled through the topology. A topological classification of entanglement is discussed, as well as properties of entanglement entropy and basic quantum protocols. The primary aim is to build a less conventional diagrammatic intuition about quantum mechanics, expanding the paradigm of “Quantum Picturalism”.

We study the behavior of the density of states and the ({B}_{1g}) nematic susceptibility extracted from Raman response data across the doping-driven Lifshitz transition comparing the weak and strong interaction cases. Our results were obtained using cluster dynamical mean field theory for the two-dimensional Hubbard model. In the weakly correlated Fermi liquid regime, both quantities are approximately symmetric around the Lifshitz transition doping (p_{LT}). In the strongly correlated regime, the low-doping pseudogap leads to an asymmetric, discontinuous evolution when the Fermi surface changes from hole-like to electron-like at (p_{LT}). The Lifshitz transition thus changes character because it is tied to the pseudogap-Fermi-liquid transition. These results are consistent with available observations and should foster further experimental investigations.

The DECY-13 cyclotron, a compact isochronous accelerator developed in Indonesia, is designed to accelerate negative hydrogen ions (H⁻) to produce radioisotopes for nuclear medicine. This study presents the methodology and implementation of a low-energy function assessment for the DECY-13, targeting the achievement of a 10 µA proton beam at 3 MeV. The assessment includes tests on subsystem functionality, magnetic field mapping, dee voltage requirements, RF power delivery, and phase synchronization between particle revolution and the RF dee field. A synchronization testing method was developed to calculate cumulative phase differences critical for stable acceleration. Results confirm successful ion beam extraction, required beam currents, and energy levels at a dee voltage of ~ 40 kV, supported by 17.57 kW RF power. Although a phase lag of 61.5° remains at 3 MeV, synchronization is maintained within acceptable limits. Further work will focus on magnetic field optimization to reduce phase deviation, enabling progression to higher-energy commissioning.

Variational quantum algorithms are promising for combinatorial optimization, but their scalability is often limited by qubit-intensive encoding schemes. To overcome this bottleneck, Pauli Correlation Encoding (PCE) has emerged as one of the most promising algorithms in this scenario. The method offers not only a polynomial reduction in qubit count and a suppression of barren plateaus but also demonstrates competitive performance with state-of-the-art methods on Maxcut. In this work, we propose a warm-start PCE, an extension that incorporates a classical bias from the Goemans-Williamson (GW) randomized rounding algorithm into the loss function to guide the optimization toward improved approximation ratios. We evaluated this method on the Traveling Salesman Problem (TSP) using a QUBO-to-MaxCut transformation for up to 5 layers. Our results show that Warm-PCE consistently outperforms standard PCE, achieving the optimum solution in (28text {--}64%) of instances, versus (4text {--}26%) for PCE, and attaining higher mean approximation ratios that improve with circuit depth. These findings highlight the practical value of this warm-start strategy for enhancing PCE-based solvers on near-term hardware.

As quantum computing hardware continues to scale, the need for a robust software infrastructure that bridges the gap between high-level algorithm development and low-level physical qubit control becomes increasingly critical. A full-stack approach, analogous to classical computing, is essential for managing complexity, enabling hardware-agnostic programming, and systematically optimizing performance. In this paper, we present a comprehensive, end-to-end quantum software stack, detailing each layer of abstraction from user-facing code to hardware execution. We begin at the highest level with the Ket quantum programming platform, which provides an expressive, Python-based interface for algorithm development. We then describe the crucial multi-stage compilation process, which translates hardware-agnostic programs into hardware-compliant circuits by handling gate decomposition, qubit mapping to respect device connectivity, and native gate translation. To illustrate the complete workflow, we present a concrete example, compiling the Grover diffusion operator for a superconducting quantum processor. Finally, we connect the compiled circuit to its physical realization by explaining how native gates are implemented through calibrated microwave pulses. This includes the calibration of single- and two-qubit gates, frequency characterization, and measurement procedures, providing a clear picture of how abstract quantum programs ultimately map onto the physical control of a quantum processor. By providing a detailed blueprint of a complete quantum stack, this work illuminates the critical interplay between software abstractions and physical hardware, establishing a framework for developing practical and performant quantum applications.

The hot and rotating isotopes of Z=120 are studied using the statistical model to determine the most probable stable isotopes and investigated their formation and the limiting temperatures. The neutron quasi-magic and magic numbers (N=178 and 184) determined from the point of shape transition, by the influence of rotation at different temperatures, are studied extensively for their thermodynamic characteristics upto the instability temperature. The interplay between level density parameter and neutron separation energy at different temperatures reveal the most probable isotope for synthesis, is (^{298})120. The occurrence of temperature dependent shape transition emphasizes the feasible temperature for the formation of (^{298})120 is T(approx)1.0-1.1 MeV with E(^{*}) ranging from (approx)36-43 MeV. A novel approach of analyzing (Delta)E(^{*}) at increasing temperature explores the thermodynamic influence on the rotating system, which gives the instability temperature at T(approx)3.3 MeV. A higher probability of synthesising (^{298})120 is predicted with an excitation energy E(^{*}approx)40 MeV at T(approx)1.0 MeV. Other studies (Wang et al. 2012; Liang et al. 2012; Li et al. 2018) have also shown that, at the same E(^{*}), for the given choice of targets and projectiles, the compound nucleus (^{298})120 can be formed; also reported by Oganessian et al. (2009).

The Dirac delta function potential is considered within the real Hilbert space approach for complex wave functions, as well as quaternionic wave functions. As has been previously determined, the real Hilbert space approach enables the possibility of self-interacting physical systems. The self-interaction precludes confining states, and also imposes non-stationary quantum states, both of them representing novel situations that cannot be observed in terms of quantum wave functions. These results remark the differences between quaternionic quantum mechanics () and complex quantum mechanics (), and also establish a method of solving the wave equation that may be applied to a variety of different cases.

A study of nuclear reactions involving the (^{30}textrm{F}) weakly bound projectile is presented. This nucleus is modeled as (^{30}textrm{F} rightarrow {}^{29}textrm{F}+n), where the core nucleus (^{29}textrm{F}) is a three-body weakly bound system ((^{29}textrm{F} rightarrow {}^{27}textrm{F}+n+n)). To study the role of this weakly bound core nucleus on the breakup observables, we proceed as follows. First, the (^{29}textrm{F}) nucleus is treated as a di-neutron system ((^{29}textrm{F} rightarrow {}^{27}textrm{F}+2n)), such that its density is (rho _{^{29}textrm{F}}(r) =rho _{^{27}textrm{F}}(r)+rho _{2n}(r)), where the di-neutron density (rho _{2n}(r)) is obtained from the ground state wave function of the (^{27}textrm{F}+2n) two-body system. The density (rho _{^{29}textrm{F}}(r)) is then used to construct a double folding potential for the (^{29}textrm{F})-target system. Second, the density (rho _{^{29}textrm{F}}(r)) is obtained from the two parameter Fermi density distribution model. The (^{29}textrm{F})-target nuclear potential is constructed within the double folding formalism by means of the DDM3Y1 and CDM3Y4 density-dependent nucleon-nucleon interactions. Analyzing the breakup cross sections, it is found that the weakly bound nature of the (^{29}textrm{F}) does not play any meaningful role in the breakup process of the (^{30}textrm{F}) nucleus on (^{40}textrm{Ar}) and (^{86})Kr noble gas targets. The novelty of this study is that it takes into account the binding energy of a weakly bound core nucleus in the breakup process of a weakly bound projectile nucleus. The proposed approach can be used to investigate the role of the breakup static effect on the suppression of the Coulomb-nuclear interference peak in the elastic scattering cross section.