Accepted Papers
Recent catalogue
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Vol.73 No.13
2024-07-05
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Vol.73 No.12
2024-06-20
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Vol.73 No.11
2024-06-05
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Vol.73 No.10
2024-05-20
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GENERAL
2024, 73 (13): 130201.
doi: 10.7498/aps.73.20240239
Abstract +
In order to alleviate the common problems of skeleton fracture and failure in traditional propulsion systems, the insulation degradation and structural instability existing in integrated drive structures during operation are investigated in this work. By using stress-strain calculations of a typical integrated drive structure and voltage-withstanding discharge tests after acceleration experiments, key factors are identified, and it is believed that the tensile stress inside the driving structure is one of the reasons for structural instability. Owing to the electromagnetic force acting on the coil, the integrated driving structure exhibits high tensile stress and strain on the inner wall and interphase partition, accompanied by significant deformation, which is not conducive to the overall structural stability. Based on the above calculation results, a novel modular drive structure with bidirectional separation is proposed, which can realize the radial separation between the phase partition and the skeleton inner cylinder, as well as axial separation between different driving coils. Finite element simulation analysis is conducted to evaluate its acceleration performance and structural response during operation. The results indicate that under the same excitation conditions, the new driving structure greatly reduces the interaction between the coil and the inner wall during operation, so the stress-strain on the inner wall of the new driving structure is much smaller than that of the integrated structure. The maximum deformation decreases from approximately 10–2 m in the integrated structure to about 10–5 m to 10–6 m in the new design. These findings emphasize the potential of new structure to improve reliability while ensuring propulsion performance, providing valuable insights for optimizing electromagnetic coil drive structures. For this new structure, there will be plans to conduct high-pressure propulsion experiments in the future to verify its reliability.
GENERAL
2024, 73 (13): 130501.
doi: 10.7498/aps.73.20231888
Abstract +
The neural network model coupled with memristors has been extensively studied due to its ability to more accurately represent the complex dynamic characteristics of the biological nervous system. Currently, the mathematical model of memristor used to couple neural networks mainly focuses on primary function, absolute value function, hyperbolic tangent function, etc. To further enrich the memristor-coupled neural network model and take into account the motion law of particles in some doped semiconductors, a new compound exponential local active memristor is proposed and used as a coupling synapse in the Hopfield neural network. Using the basic dynamic analysis method, the system’s dynamic behaviors are studied under different parameters and the coexistence of multiple bifurcation modes under different initial values. In addition, the influence of frequency change of external stimulation current on the system is also studied. The experimental results show that the internal parameters of memristor synapses regulate the system, and the system has a rich dynamic behavior, including symmetric attractor coexistence, asymmetric attractor coexistence, large-scale chaos as shown in attached figure, and bursting oscillation. Finally, the hardware of the system is realized by the STM32 microcontroller, and the experimental results verify the realization of the system.
GENERAL
2024, 73 (13): 130502.
doi: 10.7498/aps.73.20240739
Abstract +
We study the resonance exchanges of two chiral Majorana fermions in two distinct systems theoretically in this work: one is an isolated Majorana zero mode interacting with complexes formed by two chiral Majorana fermions and a Majorana zero mode, and the other involves isolated quantum dots that are coupled to a system composed of Majorana fermions and a quantum dot. Our research results reveal that both of these coupled systems can facilitate the effective transmissions of the two chiral Majorana fermions as $ {\gamma _1} \to - {\gamma _2} $ and $ {\gamma _2} \to - {\gamma _1} $ , and the resonant tunneling effects in the two systems are equivalent. Therefore, quantum dots can replace Majorana zero modes to achieve resonant tunneling. In order to observe the resonance exchange of two chiral Majorana fermions with the two quantum dots, a circuit based on anomalous quantum Hall insulator proximity-coupled with s-wave superconductor is proposed as shown in figure. The numerical results indicate that the resonant exchange of chiral Majorana fermions can be modulated by the coupling strength between the two quantum dots, and it is particularly noteworthy that the tunneling process is independent of the superconducting phase. If one of the chiral Majorana fermions undergoes resonance coupling with another quantum dot or Majorana zero mode, an additional negative sign is obtained, leading to $ - {\gamma _2} \to {\gamma _1} $ . After experiencing two resonance exchange processes, the final result is $ {\gamma _1} \to {\gamma _2} $ and $ {\gamma _2} \to - {\gamma _1} $ , which implies the realization of non-Abelian braiding operations. Our conclusion is that the modulation of coupling strength between two quantum dots can be used to achieve the switch of Majorana fermions braiding-like operation, which is independent of superconducting phase. Therefore, the designed scheme provides a new way for adjusting the braiding-like operation of Majorana fermions. These findings may have potential applications in the realization of topological quantum computers.
GENERAL
2024, 73 (13): 130503.
doi: 10.7498/aps.73.20240376
Abstract +
The quantum system composed of optical lattice and ultracold atomic gas is an ideal platform for realizing quantum simulation and quantum computing. Especially for dipolar bosons in optical lattices with artificial gauge fields, the interplay between anisotropic dipolar interactions and artificial gauge fields leads to many novel phases. Exploring the phase transition characteristics of the system is beneficial to understanding the physics of quantum many-body systems and observing quantum states of dipolar system in experiments. In this work, we investigate the quantum phase transitions of anisotropic dipolar bosons in a two-dimensional optical lattice with an artificial magnetic field. Using an inhomogeneous mean-field method and a Landau phase transition theory, we obtain complete phase diagrams and analytical expressions for phase boundaries between an incompressible phase and a compressible phase. Our results show that both the artificial magnetic field and the anisotropic dipolar interaction have a significant effect on the phase diagram. When the polar angle increases, the system undergoes the phase transition from a checkerboard supersolid to a striped supersolid. For small polar angle ($V_x/U= 0.2, V_y/U=0.1$ , Fig.(a)), artificial magnetic field induces both checkerboard solid phase and supersolid phase to extend to a large hopping region. For a larger polar angle ($V_x/U=0.2, $ $ V_y/U=-0.1$ , Fig.(b)), artificial magnetic field induces both striped solid and striped supersolid to extend to a large hopping region. Thus, the artificial magnetic field stabilizes the density wave and supersolid phases. In addition, we reveal the coexistence of different quantum phases in the presence of an external trapping potential. The research results provide a theoretical basis for manipulating the quantum phase in experiments on anisotropic dipolar atoms by using an artificial magnetic field.
Abstract +
The atomic polarizability represents the response characteristics of atoms to externally applied electro-magnetic fields. The wavelength (or frequency) at which the dynamic polarizability of an atom is equal to zero is referred to as the tune-out wavelength (or frequency). Spectroscopy technology based on the tune-out effect has potential applications in quantum precision measurement, quantum computation and quantum communication. Related research topics include the measurement of fundamental physical constants and strong interactions. The tune-out wavelengths of atoms in low-lying states primarily fall within the optical band, where the theoretical calculations and experimental measurements have significant progress. However, for Rydberg atoms in highly excited states, theoretical calculations are challenging due to their high density of atomic states. The difficulty of experimental measurement arises from small splitting of adjacent atomic energy levels. In this paper, we demonstrate the tune-out wavelengths measurement for Rydberg atoms in a cesium vapor cell at room temperature. We utilize a two-photon cascade excitation to prepare Rydberg states and employ amplitude-modulation electromagnetically-induced transparency (AM-EIT) spectroscopy to measure the tune-out wavelength. By continuously scanning the microwave frequencies, we obtain AM-EIT signals of Rydberg atoms. At near-resonant microwave transition wavelengths, strong AM-EIT signals are observed due to microwave-atom coupling. Conversely, at tune-out wavelengths, the dynamically polarization-induced destructive interference in neighboring energy states occurs which leads to the weak AM-EIT signals. The AM-EIT provides a spectral resolution of about 10 MHz. We have developed a simplified three-level model to calculate the tune-out wavelength. The results of our theoretical calculations are consistent with the experimental findings within a range of ±90 MHz.
Instrumentation and Measurement
2024, 73 (13): 130702.
doi: 10.7498/aps.73.20240560
Abstract +
The current preamplifier is one of the important components of the scanning tunneling microscope (STM), and its performance is crucial to the basic operations of the STM system, as well as for the development of demanding novel functionalities such as autonomous atomic fabrication. In this study, the factors that affect the performance of a current preamplifier, including its noise spectrum density and the bandwidth, are analyzed in depth, and a preamplifier is designed and fabricated specifically for the STM system. By using a carefully selected low-noise op amp chip, the optimized current preamplifier has a noise floor as low as 4 $ {\mathrm{f}}{\mathrm{A}}/\sqrt{{\mathrm{H}}{\mathrm{z}}} $ and a bandwidth of 2.3 kHz, at its most sensitive transimpedance gain of 1 GΩ. It has three transimpedance gains, 10 MΩ, 100 MΩ, and 1 GΩ, that can be switched through digital control signals. A two-switch configuration is adopted to minimize the noise floor while maintaining the optimal bandwidth. The current detectable by this three-level preamplifier ranges from pA to μA, satisfying the requirements of most STM operations. Using this preamplifier, the fundamental functions of the STM system are successfully demonstrated, including surface topographic characterization, scanning tunneling spectroscopy, and single atom/molecule manipulation. The measurement of shot noise in tunneling current is also explored, and a linear relationship between shot noise and tunneling current is obtained by carefully analyzing noise. It is illustrated that the Fano factor of the shot noise in a normal metallic tunneling junction is approximately equal to 1, revealing the expected Poisson process for electron tunneling in such a scenario. The results are valuable for the high-resolution characterization of correlation systems in the future.
THE PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
2024, 73 (13): 131401.
doi: 10.7498/aps.73.20240447
Abstract +
NUCLEAR PHYSICS
2024, 73 (13): 132301.
doi: 10.7498/aps.73.20240276
Abstract +
ATOMIC AND MOLECULAR PHYSICS
2024, 73 (13): 133101.
doi: 10.7498/aps.73.20240417
Abstract +
Two-dimensional tungsten disulfide (WS2), as a semiconductor material with unique layer-dependent electronic and optoelectronic characteristics, demonstrates a promising application prospect in the field of optoelectronic devices. The fabrication of wafer-scale monolayer WS2 films is currently a critical challenge that propels their application in advanced transistors and integrated circuits. Chemical vapor deposition (CVD) is a feasible technique for fabricating large-area, high-quality monolayer WS2 films, yet the complexity of its growth process results in low growth efficiency and inconsistent film quality of WS2. In order to guide experimental efforts to diminish grain boundaries in WS2, thereby improving film quality to enhance electronic performance and mechanical stability, this study investigates the nucleation mechanisms of WS2 during CVD growth through first-principles theoretical calculations. By considering chemical potential as a crucial variable, we analyze the growth energy curves of WS2 under diverse experimental conditions. Our findings demonstrate that modulating the temperature or pressure of the tungsten and sulfur precursors can decisively influence the nucleation rate of WS2. Notably, the nucleation rate reaches a peak at a tungsten source temperature of 1250 K, while an increase in sulfur source temperature or a decrease in pressure can suppress the nucleation rate, thereby enhancing the crystallinity and uniformity of monolayer WS2. These insights not only furnish a robust theoretical foundation for experimentally fine-tuning the nucleation rate as needed but also provide strategic guidance for optimizing experimental parameters to refine the crystallinity and uniformity of monolayer WS2 films. Such advancements are expected to accelerate the deployment of WS2 materials in a range of high-performance electronic devices, marking a significant stride in the field of materials science and industrial applications.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
2024, 73 (13): 134201.
doi: 10.7498/aps.73.20240269
Abstract +
Due to the boundary conditions of electromagnetic fields and phase matching of electro magnetic waves on interface being the basis to drive the Snell’s laws and Fresnel’s laws, they are also crucial for the analysis of electromagnetic wave propagation in a moving medium. There are mainly two methods to derive the boundary conditions of electromagnetic fields on moving interface. One of them is to use the kinematic integral form, yet this method is based on the classical time-space, and the other is based on the relativistic transformation, the boundary conditions are derived from the scaling effect with geometric method, or from the principle of relativity directly. However, the first one has a form the same as the form obtained by using the kinematic integral form, while the second one obtains a different form. At the same time, the phase matching of electromagnetic wave on moving interface is only discussed by Galileo transformation, however this is unreasonable, because of the relativistic effect cannot be ignored here. Therefore, it is necessary to reexamine the boundary conditions of electromagnetic fields and phase matching of electromagnetic wave on moving interface. Herein, firstly, the relativistic transformation formula of the unit normal vector of moving surface is derived from the surface equation and principle of relativity. Secondly, the boundary conditions of electromagnetic fields on moving interface are given based on the relativistic transformation formula and the non-relativistic transformation formula of the unit normal vector and electromagnetic fields, which show that the boundary conditions of electromagnetic fields on moving interface under the relativistic case and the non-relativistic case have the same form. This is not accidental but definite, because the change of flux of electromagnetic fields, like the change of magnetic flux, from the induction of electromagnetic filed is the same as that from the variation of surface element. Thirdly, the phase matching of electromagnetic wave on moving interface is given based on the relativistic transformation formula of the unit normal vector and the phase matching of electromagnetic wave on resting interface. In the problem of light incident on a homogeneous medium moving at a constant velocity in vacuum or air, using the phase matching of electromagnetic wave on moving interface, the same results can be easily obtained through other methods. The discussion in this study belongs to classical electrodynamics with no quantum effects considered, but the results will provide some conveniences for theoretically analyzing electromagnetic communication, remote sensing and telemetering.
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