Accepted Papers
Recent catalogue
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Vol.74 No.9
2025-05-05
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Vol.74 No.8
2025-04-20
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Vol.74 No.7
2025-04-05
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Vol.74 No.6
2025-03-20
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GENERAL
2025, 74 (9): 090301.
doi: 10.7498/aps.74.20250083
Abstract +
Quantum resource swapping is crucial for establishing quantum networks and achieving efficient quantum communication and it allows quantum resources to be shared and allocated between nodes in a quantum network, thereby enhancing network flexibility and quantum information processing capabilities. Quantum steering is a special type of quantum correlation that exhibits unique asymmetry compared with quantum entanglement and Bell nonlocality. This asymmetry enables quantum steering swapping to establish one-way or two-way asymmetry quantum steering between two independent optical modes, which is crucial for constructing asymmetric quantum networks. In this work, an all-optical quantum steering swapping scheme is proposed based on tripartite entangled state and bipartite entangled state. The all-optical scheme does not involve optic-electro conversion nor electro-optic conversion, but utilizes a low-noise, high-bandwidth four-wave mixing process to achieve the function of Bell state measurement in traditional schemes without measurement. After the steering swapping operation, the two originally independent entangled states without direct interaction generate quantum steering. In this work, two swapping schemes in the four-wave mixing processes, combined with linear beam splitter and nonlinear beam splitter, are investigated. By analyzing the steering characteristics of the output modes, both schemes exhibit varieties of multipartite steering types. By adjusting the transmissivity of the linear beam splitter and the gain of the four-wave mixing process, the steering relationship can be flexibly manipulated to achieve one-way and two-way asymmetry steering. This provides new possibilities for one-way quantum communication and quantum information processing, making the utilization of quantum resources more efficient and controllable. Through in-depth analysis of the steering characteristics after swapping, it is found that compared with the linear beam splitter scheme, the nonlinear beam splitter scheme not only significantly improves the capability of quantum steering, but also allows for more flexible manipulation of monogamy relations of quantum steering. By optimizing the gain parameters of the nonlinear beam splitter, the precise manipulation of the monogamy relations can be achieved over a wider range. This not only expands broader application prospects for information processing and quantum communication in quantum networks, but also lays an important foundation for building efficient and secure quantum information processing systems.
GENERAL
2025, 74 (9): 090302.
doi: 10.7498/aps.74.20250025
Abstract +
Unidimensional Gaussian modulation continuous-variable quantum key distribution (UD CV-QKD) uses only one modulator to encode information. The UD CV-QKD has the advantages of low implementation cost and low random number consumption, making it attractive for the construction of future miniaturized and low-cost large-scale quantum communication networks. However, in the actual application of the protocol, the intensity fluctuation of the source pulsed light, device defects, and external environmental interference maybe lead to the generation of source intensity errors, thereby affecting the realistic security and performance of the protocol. To solve these problems, the security and performance of UD CV-QKD are studied in depth under source intensity errors in this work. The mechanism of source intensity errors influencing the protocol parameter estimation process is analyzed. To make it possible that the protocol can operate stably under various realistic conditions and ensure communication security, three practical assumptions about the sender’s abilities are made in this work, and corresponding data optimization processing schemes for these assumptions are proposed to reduce the negative influence of source intensity errors. Additionally, both source errors and finite-size effect are comprehensively considered to ensure the realistic security of the system. The simulation results indicate that the source intensity errors cannot be neglected and the maximum transmission distance of the system will be reduced by approximately 20 km for significant intensity fluctuations. Therefore, in the practical implementation of the protocol, the influence of source intensity errors must be fully considered, and the corresponding countermeasures should be taken to reduce or even eliminate these errors. This study provides theoretical guidance for securely implementing the UD CV-QKD in real-world environments.
GENERAL
2025, 74 (9): 090303.
doi: 10.7498/aps.74.20241682
Abstract +
Continuous variable quantum key distribution (CV-QKD) has emerged as a promising candidate for quantum-secure communication due to its experimentally demonstrated high key rates in fiber-optic channels. However, the feasibility of discrete modulation CV-QKD in satellite-to-ground downlinks remains an open question due to practical challenges such as high transmission loss, limited communication windows, and atmospheric turbulence. In this work, a comprehensive framework is proposed to evaluate the feasibility of discrete modulation CV-QKD by integrating orbital dynamics and atmospheric channel models, and to comprehensively analyze the influence of the parameter space on free-space discrete modulation CV-QKD. To achieve this, a free-space CV-QKD simulation platform is employed, which calculates the elevation angle and transmission distance based on precise orbital models, thereby providing a more practical assessment of the key rate for discrete modulation CV-QKD. Simulation results verify the feasibility and practicality of discrete modulation CV-QKD in satellite-based quantum communication systems. Furthermore, the critical factors influencing the key rate performance are identified, and parameter optimization strategies are proposed, providing theoretical support for realizing the future satellite-to-ground discrete modulation CV-QKD.
REVIEW
2025, 74 (9): 090304.
doi: 10.7498/aps.74.20241262
Abstract +
This paper reviews the physical principles, development history of related application research, current research status and prospects of the Josephson voltage standard (JVS) working at liquid helium temperatures. The JVS working at liquid helium temperature has advantages of high mobility and low-energy consumption, and has a broad application prospect. This paper describes the research status of Josephson voltage standards, focusing on the possibility of developing a JVS based on high-temperature superconductors, and the challenges in chip preparation. In addition, a newly developed preparation technology for Josephson junction, namely the focused helium ion beam, is introduced. It has advantages in the preparation of high consistent Josephson junction arrays in high consistency. Therefore, it is a possible technical route for exploring the realization of JVS working at liquid helium temperature in the future.
GENERAL
2025, 74 (9): 090501.
doi: 10.7498/aps.74.20241556
Abstract +
Active particle systems are nonequilibrium systems composed of self-propelled Brownian particles, where interactions between particles can give rise to various collective behaviors. This study, based on Brownian dynamics simulations, explores the effects of light intensity, rotational diffusion coefficient, and the width and spacing of illuminated regions on the aggregation structures of the system. First, this study examines the influence of light intensity on aggregation structures under different rotational diffusion coefficients, finding that as the rotational diffusion coefficient increases, the system gradually stabilizes. This stabilization is attributed to the reduced collision effects among particles at higher diffusion coefficients. Under suitable rotational diffusion coefficients, gradually increasing the ratio of longitudinal to transverse light-induced self-propulsion forces leads to a transition in the system’s aggregation structure from a transverse stripe structure configuration to a tic-tac-toe structure, ultimately resulting in a longitudinal stripe structure. This indicates that the system’s aggregation structure can be effectively controlled by changing the relative light intensity of the longitudinal and transverse illumination. From a dynamical perspective, an unstable structure consistently exhibits a super-diffusive behavior throughout the simulations, while stable structure transitions from initial super-diffusion to normal diffusion, indicating that under steady state conditions, particles aggregate in the shaded regions, exhibiting Brownian motion. To further investigate the influence of light field on collective particle behavior, in this study the width of the illuminated region and the spacing between adjacent illuminated regions are systematically varied, finding that the overall trends are consistent with previous conclusions. It is also observed that wider illumination regions with narrower spacing contribute to the formation of tic-tac-toe structures, while narrower illumination regions with wider spacing give rise to a novel structure—checkerboard structures. This study investigates the phase separation behavior of particles in complex optical field environments, providing some valuable ideas for controlling aggregation states in active particle systems.
GENERAL
2025, 74 (9): 090502.
doi: 10.7498/aps.74.20241433
Abstract +
In this paper, various nonlinear dynamic behaviors of distributed feedback semiconductor laser (DFB-SL) subjected to self-delayed optical and electrical feedback are studied numerically. The results show that the DFB-SL output presents a variety of nonlinear dynamic states such as single-period, quasi-period, and multi-period under different optical feedback intensities. When the external light feedback reaches a certain intensity, the laser output enters a chaotic regime. When the optical feedback intensity is small, a variety of nonlinear dynamic states will appear in the DFB-SL output under different electrical feedback intensities. When the optical feedback intensity is large, the single-period dynamic state cannot be obtained by changing the electrical feedback intensity. The optical feedback and electrical feedback delay time also have a significant influence on the nonlinearity of DFB-SL. When their time delays match, the relaxation oscillation of the laser is enhanced and exhibits a single-period state. And time mismatch may lead to chaos or instability. The bias current also affects the dynamic state, however, the direction of evolution of the dynamic states is not unidirectional as the current changes unidirectionally. When the DFB-SL is in a single-period state, changing the bias current will result in the change of the single-cycle oscillation frequency. These findings provide an important theoretical basis for applying the self-delayed feedback DFB-SL to microwave photonic signal processing and secure optical communication, as well as experimental means for conducting various nonlinear scientific researches.
GENERAL
2025, 74 (9): 090701.
doi: 10.7498/aps.74.20241758
Abstract +
In this work, a low-frequency acoustic sensing scheme is proposed based on the structure of in-fiber Mach-Zehnder interferometer , in which the refractive index difference between fiber core and cladding is used to form a miniature Mach-Zehnder interferometer through fusion splicing of specialty optical fibers in a multi-mode-ultra-high numerical aperture-multi-mode configuration. This design achieves modal recombination between cladding and core modes, thereby effectively enhancing fiber bending sensitivity. The interferometer structure is then combined with a polyethylene terephthalate (PET) transducer diaphragm, enabling the sensing fiber to undergo curvature changes synchronously with the diaphragm under sound pressure, thereby indirectly increasing the area over which the fiber receives the acoustic field. When external acoustic pressure induces bending modulation on both the sensing fiber and transducer diaphragm, the differential strain distribution between the fiber cladding and core generates an optical path difference. This manifests itself in interference spectrum shifts, enabling the effective detection of low-frequency acoustic signals through demodulating the spectrum variations. In the paper, the theoretical framework for the acoustic sensing system is derived and validated experimentally. The results show that at 65 Hz, the system achieves a signal-to-noise ratio (SNR) of approximately 57 dB and a minimum detectable sound pressure of $267.9{\text{ μPa/H}}{{\text{z}}^{{{1/2}}}}$at 65 Hz. In a frequency range of 50–500 Hz, the system exhibits good acoustic response, with an SNR consistently above 40 dB and a relatively flat signal output. This scheme significantly enhances the acoustic response capability of the sensing system, enabling the effective detection of low-frequency acoustic waves. Additionally, it features simple fabrication and low cost, showing great potential for the development of acoustic wave detection applications.
GENERAL
2025, 74 (9): 090702.
doi: 10.7498/aps.74.20241634
Abstract +
With the state-of-the-art quantum measurement devices, such as atomic clocks, atomic gyroscopes, and atomic magnetometers, as their central components, the spatiotemporal evolution of atomic spin polarization in the atomic vapor cell has a major effect on both increasing the bandwidth of magnetometer and improving the accuracy of magnetic gradient measurements. However, the major factor impeding the further improvement of the performance of quantum measurement instrument is the inherent static nature of the traditional intra-vapor cell segmentation imaging technique, which makes it challenging to achieve the real-time capture of the dynamic evolution of atomic spin states. In this work, we suggest a dynamic spin imaging method for alkali metal atomic vapor cells with real-time modification of atomic spin polarization states in order to overcome this technological difficulty. In particular, to ensure that the laser can precisely act on the alkali metal atoms in various regions in the vapor cell, we employ a complex beam array management system to modify the on/off state of the laser beams at various positions in the spatial dimension in real time. In the meantime, we generate laser fields with particular spatial distribution and frequency characteristics by using frequency modulation techniques in the time series to accurately regulate the on-off frequency of each laser beam in the beam array. These laser beams cause dynamic changes in the atomic spin polarization state by interacting with alkali metal atoms at various points in the vapor cell. Through precise adjustment of the laser properties, we can see and study the dynamic evolution of the atomic spin-polarization state in real time. According to the experimental data, the technology outperforms the traditional static spin imaging techniques by achieving an excellent temporal resolution of 355 frames per second and a spatial resolution of 95.9 micrometers. The effective use of this method enables us to monitor and evaluate the dynamic aspects of magnetic field distribution with unprecedented precision, also greatly enhance our understanding of the dynamic characteristics of atomic spin polarization.
NUCLEAR PHYSICS
2025, 74 (9): 092801.
doi: 10.7498/aps.74.20241755
Abstract +
The ion cyclotron resonance (ICR) isotope separation method is an advanced electromagnetic separation method. The key process of this method is the transport of ions in an axial magnetic field. By injecting microwaves at the target ion cyclotron frequency, only the target ions can be heated so that the energy values of target ions can be distinguished. Due to its high separation coefficient, multiple types of isotopes that can be separated, and high flux, some countries have already built ICR isotope separation devices and conducted various isotope separation experiments since 1980. The main elements of an ICR separation device include three parts: a plasma source, a selective ion heating system, and an ion collector. The electron cyclotron resonance (ECR) ion source is the most popular plasma source, which generates the ions to be separated. The selective ion heating system is the key part of the separation device, mainly composed of a superconducting magnetic coil and a radio frequency (RF) antenna, which are used to provide a stable magnetic field and microwaves at a specific frequency to heat the target isotope ions, respectively. The ion collector is used to collect the separated ions. To clarify the key process of the ICR separation method, the transport process of ions in the electromagnetic field inside the selective ion heating system is simulated, and the influences on the selective heating effects of core parameters, such as parameters of initial plasma beam and electromagnetic field inside the selective ion heating system, are discussed in detail. The numerical simulation model used in this study is the single particle model, in which the interaction between ions and the induced electromagnetic field of the plasma beam is ignored. The simulation results show that the intensity of the alternating electric field in the selective ion heating system, the wavelength of the RF antenna, the size of the ion selective heating system, the initial axial energy of the plasma and its distribution all have a significant influence on the overall heating effect of the plasma beam. The magnetic induction intensity in the ion selective heating system, the wavelength of the RF antenna, and the initial axial energy distribution of the plasma have a direct influence on the selectivity of the heating process. Considering the limitations of the single particle model, a more accurate model will be used for further simulation. The design of the RF antenna and ECR ion source will also be considered in the further research.
SPECIAL TOPIC—Dynamics of atoms and molecules at extremes
2025, 74 (9): 093201.
doi: 10.7498/aps.74.20241792
Abstract +
The study of atomic and molecular structure imaging is of great significance in revealing the microscopic nature of matter and promoting the frontier development of materials science and life science. The rapid development of femtosecond laser technology provides a new method for detecting atomic and molecular structures on an ultrafast time scale, such as strong-field tomography scheme. Strong-field tomography uses strong-field driven electron rescattering to detect the structure of oriented molecules. The advantage of this scheme is that it does not require priori knowledge of atomic differential cross-sections. Using the strong-field tomography scheme, the structural extraction of homonuclear diatomic molecules can be realized successfully. However, it is currently unclear whether this imaging scheme is applicable to the heteronuclear molecular system with more complex cross section of the electron. In this work, heteronuclear diatomic molecules are taken for example and the strong-field tomography scheme is used to study the imaging of the molecular structure. By solving the time-dependent Schrödinger equation, the variation of the photoelectron yield with the orientation angle of the molecular axis is obtained. Next, a fitting method for the variation of the photoelectron yields of the heteronuclear molecules with the orientation angle is presented, and then the fitted value of the internuclear separation is obtained. It is found that the fitting result is comparable to the real molecular internuclear separation, indicating that the strong-field tomography scheme is also suitable for the extraction of heteronuclear molecular structural information.
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