In Press
In Press catalogue
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Vol.74 No.19
2025-10-05
2025, 74 (19): 190201.
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Realizing the independent control of the national standard time has important practical significance under the current international situation. In this work, an independent time scale that does not rely on external references is developed by studying the self-developed cesium fountain primary frequency standard and domestically-produced optically-pumped small cesium clocks. The specific approach is to use the cesium fountain primary frequency standard as a frequency reference to predict the frequency drift of the optically pumped small cesium clocks. By analyzing the noise characteristics of the optically pumped small cesium clocks, the state equation of the atomic clock is established, and the state of the optically pumped small cesium clock is estimated based on the Kalman filtering algorithm. The calculation of the time scale is based on the frequency state estimation and frequency drift state estimation of atomic clocks, which serve as the forecast values, and is achieved through the weight algorithm. The weight algorithm based on prediction error and the weight algorithm based on noise characteristics are studied. The results show that in the case of using Kalman filtering state estimation, the weight algorithm based on prediction error significantly improves the accuracy of the independent time scale. The cesium fountain primary frequency standard is chosen as the frequency reference to predict the frequency drift of the optically pumped small cesium clock. The accuracy and long-term stability of the independent time scale calculated are much better than those when the time scale itself is used as the frequency reference. Taking the international standard time (UTCr) as the reference, the accuracy of the independent time scale is maintained within 15 ns. The frequency stability is 1.57×10–14 for a sampling interval of 1 day, 4.29×10–15 for a sampling interval of 15 days, and 2.87×10–15 for a sampling interval of 30 days is showing that its stability can meet the current national time demand.
2025, 74 (19): 190202.
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The structured light 3D measurement technology based on laser galvanometer has been widely used in industrial scenarios such as robot grasping, handling, and loading/unloading in welding and assembly workshops. However, in actual measurement scenarios, there are complex measurement structures such as depressions, overlaps, and occlusions. Light is prone to multiple reflections between micro-faces, causing intensity information to be mixed within the micro-face area and ultimately resulting in point cloud loss in this measurement area. To address the issue of point cloud loss in complex structure areas in the measurement process and ensure the accuracy of the measurement information provided by vision, a binocular point cloud sensor with a laser galvanometer as the key projection module is proposed in this work. Without adding hardware, it realizes two different image projection modes to deal with complex measurement situations within the scene. Among them, the anti-multiple reflection projection mode proposed in this work, by regulating the timing coordination relationship between key components, completes the measurement of complex structure positions and solves the problem of point cloud loss caused by multiple reflection interference. Finally, multiple experiments are conducted in actual scenarios to verify the feasibility of the proposed strategy. The experimental results show that in measurement scenarios with multiple reflection interference, the integrity of the black part point cloud measured by the anti-multiple reflection projection mode proposed in this work reaches 98.03%, which is 18.98% higher than the traditional measurement mode. It effectively solves the problem of point cloud loss in measurement scenarios with multiple reflection interference. Visual measurements ensure the accuracy and completeness of the information obtained. The six-axis compensation values determined by the robot for each part’s pose state during teaching become more precise. This ensures that the previously taught robot trajectory can be accurately reused for subsequent poses, thereby reducing the time needed for manual robot debugging and enhancing production efficiency.
2025, 74 (19): 190203.
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Photonic crystals have received widespread attention in the field of photonics due to their unique band structures, which can manipulate the propagation of light through periodic dielectric arrangements. Accurate prediction of these band structures is crucial for designing and optimizing photonic devices. However, traditional numerical simulation methods, such as plane wave expansion and finite element methods, are often limited by high computational complexity and long processing times. In this study, we explore the application of the vision transformer (ViT) model to predicting the band structures of photonic crystals efficiently and accurately. To further validate the superiority of the ViT model, we also conduct experiments by using CNN and MLP models on the same scale for band structure prediction. We first generate a dataset of photonic band structures by using traditional numerical simulations and then train the ViT model on this dataset. The ViT model demonstrates excellent learning capabilities, with the loss function value decreasing to as low as 4.42×10–6 during training. The test results show that the average mean squared (MSE) error of the ViT model predictions is 3.46×10–5, and the coefficient of determination (R2) reaches 0.9996, indicating high prediction accuracy and good generalization capability. In contrast, the CNN and MLP models, despite being trained on the same dataset and having the same computational resource allocation, show higher MSE values and lower R2 scores. This highlights the superior performance of the ViT model in predicting the band structures of photonic crystals. Our study shows that the ViT model can effectively predict the band structures of photonic crystals, providing a new and efficient prediction tool for relevant research and applications. This work is expected to advance the development of photonic device design by offering a rapid and accurate alternative to traditional methods.
2025, 74 (19): 190301.
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Entanglement detection and classification of multipartite systems remain the key topics in the field of quantum information and science. In this work, we take advantage of the nature that quantum Fisher information (QFI) can witness multipartite entanglement to comprehensively investigate the entanglement detection and classification of multi-qubit $W{\overline{W}} $ states immersed in a white noise environment. In the situation of local operation, by combining the information of the known quantum state, we have presented a criterion with visibility for witnessing the genuine multipartite entanglement and another for identifying the presence of quantum entanglement. Specifically, with respect to the 5-qubit $W{\overline{W}} $ state and 6-qubit $W{\overline{W}} $ state, due to the fact that the maximum QFI of their splitting-structure states exceeds that of the original states, it is infeasible to strictly establish a criterion for detecting the genuine multipartite entanglement. However, we delineate the scope for inferring the possible entanglement structures. Furthermore, it is found that as the number of qubits increases, the conditions for witnessing the genuine multipartite entanglement become increasingly strict, while those for detecting the existence of entanglement grow relatively more relaxed. Taking into account the likelihood of the crosstalk between neighboring qubits during the local operations on the multipartite systems in experiments, we employ the Lipkin-Meshkov-Glick (LMG) model to explore the entanglement classification of diverse multi-qubit multipartite states. It is found that with the increasing interaction strength, even for the strong white noise, the $W{\overline{W}} $ states can still be distinguished, thereby resolving the challenge of managing the entanglement classification under local operation. Besides, as the interaction strength continues to increase, the task of entanglement classification becomes more straightforward. This fully shows the superiority of nonlocal operations over local operations in the aspect of entanglement classification.
2025, 74 (19): 190302.
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2025, 74 (19): 190303.
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By numerically solving the single-particle stationary Schrödinger equation and the Gross-Pitaevskii equation with mean-field interactions at zero temperature, the ground state properties of the rotating spin-orbital-angular-momentum coupled Bose-Einstein condensates in a harmonic trapping potential are investigated in this work. The results show that the rotation lifts the double degeneracy of the single-particle energy spectrum in the angular momentum space, and leads to the vortex state. The angular momentum of the vortex depends on the rotating frequency, the intensity of the laser beam, and the spin-orbital-angular-momentum coupling. In particular, if the rotating frequency is below a critical value, the angular momentum of the ground state vortex remains unaffected by the rotating frequency. When the rotating frequency exceeds the critical value, the angular momentum of the ground state vortex will increase with the rotating frequency increasing. By assuming that the system is confined in a ring trap, the expression of the single-particle energy spectrum in the angular momentum space can be obtained, which clarifies how the rotation frequency affects the angular momentum of the ground state. In the presence of atomic interactions, similar phenomena can also be observed in the mean-field ground state at zero temperature.
2025, 74 (19): 190701.
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The fiber Bragg grating has the characteristics of anti-electromagnetic interference, electrically passive operation, multi-point sensing, corrosion resistance, and compact size. An ultra-narrow linewidth transmission peak can be formed by introducing a π phase shift at the center of uniform fiber Bragg grating. But this π phase-shifted fiber Bragg grating (PSFBG) with an ultra-narrow linewidth is very sensitive to the input optical intensity. The photothermal effect generated by the input light inside the grating will cause the frequency shift, which will degrade the measurement precision of grating. At the same time, the frequency drift of the laser itself will also increase the measurement error. In this paper, a high-precision strain measurement method is proposed by using the PSFBG with an ultra-narrow linewidth based on the frequency-stabilized laser. The incident laser is attenuated to a single-photon level to eliminate the photothermal effect in the PSFBG. The laser frequency is stabilized to the PSFBG with an ultra-narrow linewidth of 38 MHz by using the single-photon modulation technology. The influence of low-frequency flicker noise is eliminated through 9-kHz high-frequency modulation. The filter bandwidth of lock-in amplifier is 312.5 Hz with the integration time and filter slope of 300 μs and 18 dB, respectively. The signal-to-noise ratio of error signal from the lock-in amplifier is 34. By tuning the resonant cavity length of the laser with the error signal, the output laser frequency is stabilized to the Bragg frequency of the PSFBG with an ultra-narrow linewidth of 38 MHz. The laser frequency fluctuation is limited to 4 MHz within 1000 s. The response sensitivity of Bragg wavelength to external strain in a range of 0 to 30 με is 1.2 pm/με, with a standard error of 0.023 pm/με, and the linear fitting correlation coefficient is R2 = 0.997. Due to the random drift of Bragg wavelength, caused by the environment temperature fluctuations, the corresponding strain measurement precision is 0.05 με. The high-precision strain measurement by using the PSFBG with an ultra-narrow linewidth based on the frequency-stabilized laser is achieved, which will play an important role in the field of aerospace, civil engineering, energy engineering, etc.
2025, 74 (19): 192101.
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2025, 74 (19): 192301.
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2025, 74 (19): 192901.
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