Chenrui Zhao, Yunxin Wei, Tingting Liu, and Minghui Qin
Ferrimagnetic domain walls are attracting more and more attentions due to their interesting physics and potential applications in future spintronic devices, particularly attributes to the non-zero net magnetization and ultrafast dynamic properties. Exploring effective methods for driving domain walls with low energy consumption and high efficiency does provide important information for experimental design and device development. In this work, we study theoretically and numerically the dynamics of ferrimagnetic domain wall driven by the sinusoidal microwave magnetic field using the collective coordinate theory and Landau-Lifshitz-Gilbert simulations of atomistic spin model. It is revealed that the microwave field can drive the propagation of the domain wall along nanowires when the frequency falls into appropriate regions, which allows one to modulate the domain wall dynamics through tuning field frequency. Specifically, the domain wall velocity is proportional to the field frequency and the net angular momentum below the critical frequency, while it quickly decreases to zero above the critical frequency. The physical mechanisms of the results are discussed in detail, and the influences of the biaxial anisotropy and other parameters on the velocity of domain wall are explored. Thus, it is suggested that the domain wall dynamics can be effectively regulated by adjusting the basic magnetic structure and magnetic anisotropic, in addition to the external microwave field frequency. This work uncovers interesint dynamics of ferrimagnetic domain wall driven by sinusoidal microwave magnetic field, which is helpful for domain wall-based spintronic device design.
{"title":"Domain wall dynamics driven by sinusoidal polarized magnetic field in ferrimagnets","authors":"Chenrui Zhao, Yunxin Wei, Tingting Liu, and Minghui Qin","doi":"10.7498/aps.72.20230913","DOIUrl":"https://doi.org/10.7498/aps.72.20230913","url":null,"abstract":"Ferrimagnetic domain walls are attracting more and more attentions due to their interesting physics and potential applications in future spintronic devices, particularly attributes to the non-zero net magnetization and ultrafast dynamic properties. Exploring effective methods for driving domain walls with low energy consumption and high efficiency does provide important information for experimental design and device development. In this work, we study theoretically and numerically the dynamics of ferrimagnetic domain wall driven by the sinusoidal microwave magnetic field using the collective coordinate theory and Landau-Lifshitz-Gilbert simulations of atomistic spin model. It is revealed that the microwave field can drive the propagation of the domain wall along nanowires when the frequency falls into appropriate regions, which allows one to modulate the domain wall dynamics through tuning field frequency. Specifically, the domain wall velocity is proportional to the field frequency and the net angular momentum below the critical frequency, while it quickly decreases to zero above the critical frequency. The physical mechanisms of the results are discussed in detail, and the influences of the biaxial anisotropy and other parameters on the velocity of domain wall are explored. Thus, it is suggested that the domain wall dynamics can be effectively regulated by adjusting the basic magnetic structure and magnetic anisotropic, in addition to the external microwave field frequency. This work uncovers interesint dynamics of ferrimagnetic domain wall driven by sinusoidal microwave magnetic field, which is helpful for domain wall-based spintronic device design.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"38 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87088658","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Nowadays, there are enormous amounts of energy wasted in the world, most of which is in the form of waste heat. Thermoelectric effect, by converting heat energy into electricity without the release of dangerous substances, has attracted more and more interest from researchers. Since the discovery of graphene, more and more twodimensional layered materials have been reported, which typically own superior electrical, optical and other physical properties than that of bulk materials, and the development of the new theory and experiment technologies stimulates further research for them as well. In this paper, we firstly introduce the measurement methods and techniques that are appropriate for the thermoelectric properties characterizations of two-dimensional materials, and then discuss the current challenging issues related to that. Subsequently, graphene, transition metal disulfides, black phosphorus and other 2D materials in thermoelectric applications are introduced. Finally, we discuss the various strategies to improve the thermoelectric performance and the problems that need to be solved urgently.
{"title":"Recent progresses of two-dimensional layered thermoelectric materials","authors":"Zehao Yu, Lifa Zhang, Jing Wu, Yunshan Zhao","doi":"10.7498/aps.72.20222095","DOIUrl":"https://doi.org/10.7498/aps.72.20222095","url":null,"abstract":"Nowadays, there are enormous amounts of energy wasted in the world, most of which is in the form of waste heat. Thermoelectric effect, by converting heat energy into electricity without the release of dangerous substances, has attracted more and more interest from researchers. Since the discovery of graphene, more and more twodimensional layered materials have been reported, which typically own superior electrical, optical and other physical properties than that of bulk materials, and the development of the new theory and experiment technologies stimulates further research for them as well. In this paper, we firstly introduce the measurement methods and techniques that are appropriate for the thermoelectric properties characterizations of two-dimensional materials, and then discuss the current challenging issues related to that. Subsequently, graphene, transition metal disulfides, black phosphorus and other 2D materials in thermoelectric applications are introduced. Finally, we discuss the various strategies to improve the thermoelectric performance and the problems that need to be solved urgently.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"100 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86291947","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The problem of sharing quantum correlations is an interesting problem in the study of quantum information theory. Silva et al. proposed the study of sharing quantum nonlocality at first. They studied the fundamental limits on nonlocality, asking whether a single pair of entangled qubits could generate a long sequence of nonlocal correlations. At the same time, the sequential scenario was also introduced first, in which Alice and Bob each have half of a pair of entangled qubit states. The first Bob measures his half and then passes his part to a second Bob who measures again and so on. Obviously, even partial preservation of entanglement in a shared state in spite of a few sequences of local operations performed by the sharing parties can be important for information processing schemes in which entanglement is utilized as a resource. Thus, the problem of sharing quantum entanglement has also been extensively investigated. Recently, C. Srivastava et al. proved that there exist a class of T-states whose entanglement can be shared by arbitrarily many independent observers in[Phys. Rev. A 2022 105 062413]. Here, we want to find whether there are other entangled states that can be shared entanglement arbitrarily many times. In this paper, we consider the problem of sharing quantum entanglement when the initial shared state is a two-qubit entangled Werner state. The goal is to maximize the number of Bobs that can share entanglement with a single Alice. By suitably choosing the entanglement witness operator and the unsharp measurement settings by the Bobs, we prove that there exist two-qubit entangled initial shared Werner states whose entanglement can be detected by arbitrarily many sequential observers Bobs with a single Alice. Then, we also consider the special case of the Werner state, that is, the maximally entangled state as the initial shared state. In this case, its entanglement can also be witnessed arbitrarily many times, and the number of Bobs increases with the decrease of parameter.
{"title":"Sharing entanglement of the Werner state by arbitrarily many independent observers","authors":"Yu Xin-Miao, Yang Shu-Yuan, He Kan","doi":"10.7498/aps.72.20222039","DOIUrl":"https://doi.org/10.7498/aps.72.20222039","url":null,"abstract":"The problem of sharing quantum correlations is an interesting problem in the study of quantum information theory. Silva et al. proposed the study of sharing quantum nonlocality at first. They studied the fundamental limits on nonlocality, asking whether a single pair of entangled qubits could generate a long sequence of nonlocal correlations. At the same time, the sequential scenario was also introduced first, in which Alice and Bob each have half of a pair of entangled qubit states. The first Bob measures his half and then passes his part to a second Bob who measures again and so on. Obviously, even partial preservation of entanglement in a shared state in spite of a few sequences of local operations performed by the sharing parties can be important for information processing schemes in which entanglement is utilized as a resource. Thus, the problem of sharing quantum entanglement has also been extensively investigated. Recently, C. Srivastava et al. proved that there exist a class of T-states whose entanglement can be shared by arbitrarily many independent observers in[Phys. Rev. A 2022 105 062413]. Here, we want to find whether there are other entangled states that can be shared entanglement arbitrarily many times. In this paper, we consider the problem of sharing quantum entanglement when the initial shared state is a two-qubit entangled Werner state. The goal is to maximize the number of Bobs that can share entanglement with a single Alice. By suitably choosing the entanglement witness operator and the unsharp measurement settings by the Bobs, we prove that there exist two-qubit entangled initial shared Werner states whose entanglement can be detected by arbitrarily many sequential observers Bobs with a single Alice. Then, we also consider the special case of the Werner state, that is, the maximally entangled state as the initial shared state. In this case, its entanglement can also be witnessed arbitrarily many times, and the number of Bobs increases with the decrease of parameter.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"105 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80719068","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
LIU Tianle, XU Xiao, FU Bowei, XU Jiaxin, LIU Jingyang, ZHOU Xingyu, WANG Qin
The parameter configuration of Quantum Key Distribution (QKD) has a great impact on the communication effect, and in the practical application of the QKD network in the future, it is necessary to quickly realize the parameter configuration optimization of the asymmetric channel Measurement-Device-Independent QKD according to the communication state, so as to ensure the good communication effect of the mobile users, which is an inevitable requirement for real-time quantum communication. Aiming at the problem that the traditional QKD parameter optimization configuration scheme cannot guarantee real-time, this paper proposes to apply the supervised machine learning algorithm to the QKD parameter optimization configuration, and predict the optimal parameters of TF-QKD and MDI-QKD under different conditions through the machine learning model. First, we delineated the range of system parameters and evenly spaced (linear or logarithmic) values through experimental experience. Then, use the traditional Local Search Algorithm(LSA) to obtain the optimal parameters and take them as the optimal parameters in this paper. Finally, we train various machine learning models based on the above data and compare their performance. We compare the supervised regression learning models such as Neural Network, KNeighbors, Random Forest, Gradient Tree Boosting and Classification And Regression Tree (CART), and the results show that the CART decision tree model has the best performance on the regression evaluation index, and the average value of the key rate (of the prediction parameters) and the optimal key rate ratio is about 0.995, which can meet the communication needs in the actual environment. At the same time, the CART decision tree model shows good environmental robustness in the residual analysis of asymmetric QKD protocol. In addition, compared with the traditional scheme, the new scheme based on CART decision tree has greatly improved the real-time performance of computing, shortening the single prediction time of the optimal parameters of different environments to the order of microseconds, which well meets the real-time communication needs of the communicator in the mobile state. This paper mainly focuses on the parameter optimization of Discrete Variable QKD (DV QKD). In recent years, the development of Continuous Variable QKD (CV QKD) is also rapid. At the end of the paper, we briefly introduce the academic attempts to apply machine learning to the parameter optimization of CV QKD system. And discusses the applicability of the scheme in this paper to the CV QKD system.
{"title":"Parameter optimization of Measurement-Device-Independent Quantum Key Distribution based on regression decision tree","authors":"LIU Tianle, XU Xiao, FU Bowei, XU Jiaxin, LIU Jingyang, ZHOU Xingyu, WANG Qin","doi":"10.7498/aps.72.20230160","DOIUrl":"https://doi.org/10.7498/aps.72.20230160","url":null,"abstract":"The parameter configuration of Quantum Key Distribution (QKD) has a great impact on the communication effect, and in the practical application of the QKD network in the future, it is necessary to quickly realize the parameter configuration optimization of the asymmetric channel Measurement-Device-Independent QKD according to the communication state, so as to ensure the good communication effect of the mobile users, which is an inevitable requirement for real-time quantum communication. Aiming at the problem that the traditional QKD parameter optimization configuration scheme cannot guarantee real-time, this paper proposes to apply the supervised machine learning algorithm to the QKD parameter optimization configuration, and predict the optimal parameters of TF-QKD and MDI-QKD under different conditions through the machine learning model. First, we delineated the range of system parameters and evenly spaced (linear or logarithmic) values through experimental experience. Then, use the traditional Local Search Algorithm(LSA) to obtain the optimal parameters and take them as the optimal parameters in this paper. Finally, we train various machine learning models based on the above data and compare their performance. We compare the supervised regression learning models such as Neural Network, KNeighbors, Random Forest, Gradient Tree Boosting and Classification And Regression Tree (CART), and the results show that the CART decision tree model has the best performance on the regression evaluation index, and the average value of the key rate (of the prediction parameters) and the optimal key rate ratio is about 0.995, which can meet the communication needs in the actual environment. At the same time, the CART decision tree model shows good environmental robustness in the residual analysis of asymmetric QKD protocol. In addition, compared with the traditional scheme, the new scheme based on CART decision tree has greatly improved the real-time performance of computing, shortening the single prediction time of the optimal parameters of different environments to the order of microseconds, which well meets the real-time communication needs of the communicator in the mobile state. This paper mainly focuses on the parameter optimization of Discrete Variable QKD (DV QKD). In recent years, the development of Continuous Variable QKD (CV QKD) is also rapid. At the end of the paper, we briefly introduce the academic attempts to apply machine learning to the parameter optimization of CV QKD system. And discusses the applicability of the scheme in this paper to the CV QKD system.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"22 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83529590","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zhang Zhi-da, Yi Kang-yuan, Chen Yuan-zhen, Yan Fei
Dynamical decoupling refers to a family of techniques that are widely used to suppress decoherence in various quantum systems caused by quasi-static environmental noise. They have broad applications in the field of quantum information processing. Conventional dynamical decoupling targets at noise in two-level systems such as qubits and often consists specifically engineered sequences of π pulses that swap between two different states. On the other hand, researchers have gone beyond simple two-levels systems seeking for even more efficient quantum hardware. A variety of quantum algorithms and schemes of quantum control using multi-level systems, such as qutrits and qudits, for quantum information processing have been proposed and some of them being implemented successfully. However, decoherence in such multi-level systems is inherently more sophisticated than that in two-level systems. So far there has been little systematic research on how to tackle decoherence issues in such systems. In this work, we propose several sequences of dynamical decoupling for 19 multi-level systems that only rely on π pulses linking neighboring levels, which is experimentally friendly. Our results show that these sequences can efficiently suppress quasi-static noise presented in multi-level systems. In addition, by calculating the corresponding filter functions of these sequences, we are able to further analyze the effect of them on generic Gaussian noise that may not be quasi-static. We also give a physical interpretation of the noise filtering mechanism of these sequences by considering their control functions. Other topics discussed in our work include power spectral density and correlation of noise in multi-level systems. Our work represents a first step towards a more systematic investigation of dynamical decoupling techniques applicable to multilevel systems.
{"title":"Dynamic decoupling for multi-level systems","authors":"Zhang Zhi-da, Yi Kang-yuan, Chen Yuan-zhen, Yan Fei","doi":"10.7498/aps.72.20222398","DOIUrl":"https://doi.org/10.7498/aps.72.20222398","url":null,"abstract":"Dynamical decoupling refers to a family of techniques that are widely used to suppress decoherence in various quantum systems caused by quasi-static environmental noise. They have broad applications in the field of quantum information processing. Conventional dynamical decoupling targets at noise in two-level systems such as qubits and often consists specifically engineered sequences of π pulses that swap between two different states. On the other hand, researchers have gone beyond simple two-levels systems seeking for even more efficient quantum hardware. A variety of quantum algorithms and schemes of quantum control using multi-level systems, such as qutrits and qudits, for quantum information processing have been proposed and some of them being implemented successfully. However, decoherence in such multi-level systems is inherently more sophisticated than that in two-level systems. So far there has been little systematic research on how to tackle decoherence issues in such systems. In this work, we propose several sequences of dynamical decoupling for 19 multi-level systems that only rely on π pulses linking neighboring levels, which is experimentally friendly. Our results show that these sequences can efficiently suppress quasi-static noise presented in multi-level systems. In addition, by calculating the corresponding filter functions of these sequences, we are able to further analyze the effect of them on generic Gaussian noise that may not be quasi-static. We also give a physical interpretation of the noise filtering mechanism of these sequences by considering their control functions. Other topics discussed in our work include power spectral density and correlation of noise in multi-level systems. Our work represents a first step towards a more systematic investigation of dynamical decoupling techniques applicable to multilevel systems.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"223 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83652689","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jing Chen-Xuan, Shi Sheng-Guo, Yang De-Sen, Zhang Jiang-Yi, Li Song
The scattering of sound waves by underwater vortex flow filed is the basic problem of sound waves propagating in complex flow fields, which has important significance in underwater target detection and sound imaging of flow field. The theoretical analysis model and numerical calculation method are established for the problem of sound scattering modulation in underwater low frequency oscillating vortex flow fields, and the generation mechanism and time frequency and space characteristics of the scattering modulation sound field are explored. Firstly, based on the wave equation of the moving medium, under the first-order approximation, the wave equation is decomposed into the flow-sound coupling term and the non flow-sound coupling term by introducing a potential function, and the flow-sound coupling term is analyzed in the frequency domain, revealing the underwater oscillating vortex flow field. Secondly, the discontinuous Galerkin numerical calculation method is used to solve the wave equation of the moving medium, and the sound propagation process in the underwater low frequency oscillating vortex flow field is numerically simulated. Under the condition of low Mach number, the effects of different incident sound frequency, the oscillation frequency of the vortex flow field and the scale of the vortex core on the time-frequency and space characteristics of the scattering modulating sound fields of vortex flow field are analyzed, and theoretical analysis model is used to explain the characteristics.The research results show that: under the condition of low Mach number, the scattering of sound wave by oscillating vortex flow field can produce a scattering modulated sound field containing the harmonic of oscillating frequency side frequency modulation. The amplitude of the scattered sound pressure changes periodically with time, and the forward scattering is much stronger than the backward scattering. The fundamental frequency scattering modulation is much stronger than the frequency doubling scattering modulation. With the increase of the frequency of the incident sound wave and the scale of the vortex core, the intensity of the scattering modulating sound field increases, and the spatial distribution of the total scattering sound field has symmetry and an obvious main lobe, the main lobe is gradually sharpened, the azimuth angle of the main lobe is close to the propagation direction of the incident wave. When the frequency ratio is much greater than 1, the vortex flow field oscillation frequency has little effect on the spatial distribution of the sound field intensity of scattering modulating sound field.
{"title":"Study on mechanism and characteristics of sound scattering modulation by underwater low frequency oscillating vortex flow field","authors":"Jing Chen-Xuan, Shi Sheng-Guo, Yang De-Sen, Zhang Jiang-Yi, Li Song","doi":"10.7498/aps.72.20221748","DOIUrl":"https://doi.org/10.7498/aps.72.20221748","url":null,"abstract":"The scattering of sound waves by underwater vortex flow filed is the basic problem of sound waves propagating in complex flow fields, which has important significance in underwater target detection and sound imaging of flow field. The theoretical analysis model and numerical calculation method are established for the problem of sound scattering modulation in underwater low frequency oscillating vortex flow fields, and the generation mechanism and time frequency and space characteristics of the scattering modulation sound field are explored. Firstly, based on the wave equation of the moving medium, under the first-order approximation, the wave equation is decomposed into the flow-sound coupling term and the non flow-sound coupling term by introducing a potential function, and the flow-sound coupling term is analyzed in the frequency domain, revealing the underwater oscillating vortex flow field. Secondly, the discontinuous Galerkin numerical calculation method is used to solve the wave equation of the moving medium, and the sound propagation process in the underwater low frequency oscillating vortex flow field is numerically simulated. Under the condition of low Mach number, the effects of different incident sound frequency, the oscillation frequency of the vortex flow field and the scale of the vortex core on the time-frequency and space characteristics of the scattering modulating sound fields of vortex flow field are analyzed, and theoretical analysis model is used to explain the characteristics.The research results show that: under the condition of low Mach number, the scattering of sound wave by oscillating vortex flow field can produce a scattering modulated sound field containing the harmonic of oscillating frequency side frequency modulation. The amplitude of the scattered sound pressure changes periodically with time, and the forward scattering is much stronger than the backward scattering. The fundamental frequency scattering modulation is much stronger than the frequency doubling scattering modulation. With the increase of the frequency of the incident sound wave and the scale of the vortex core, the intensity of the scattering modulating sound field increases, and the spatial distribution of the total scattering sound field has symmetry and an obvious main lobe, the main lobe is gradually sharpened, the azimuth angle of the main lobe is close to the propagation direction of the incident wave. When the frequency ratio is much greater than 1, the vortex flow field oscillation frequency has little effect on the spatial distribution of the sound field intensity of scattering modulating sound field.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"30 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83785960","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Li De-Zhang, Lu Zhi-Wei, Zhao Yu-Jun, Yang Xiao-Bao
The stochastic dynamics of spin semiclassical system at finite temperature is usually described by stochastic Landau-Lifshitz equation. In this work, the stochastic differential equation for spin semiclassical system is studied. The generalized formulation of effective Langevin equation and the corresponding Fokker-Planck equation are derived. The obtained effective Langevin equation offers an accurate description of the distribution in the canonical ensemble for spin semiclassical system. When the damping term and the stochastic term vanish, the effective Langevin equation reduces to the semiclassical equation of motion for spin system. Hence, the effective Langevin equation can be seen as a generalization of the stochastic Landau-Lifshitz equation. The explicit expressions for the effective Langevin equation and the corresponding Fokker-Planck equation are shown in both Cartesian and Spherical coordinates. It is demonstrated that, the longitudinal effect can be easily illustrated from the expressions in Spherical coordinates. The effective Langevin equation is applied to the simple system of a single spin in a constant magnetic field. In choosing an appropriate form, the Langevin equation can be easily solved and the stationary Boltzmann distribution can be obtained. The correctness of the Langevin approach to the spin semiclassical system is thus confirmed.
{"title":"Study of the generalization of spin semiclassical Langevin equation","authors":"Li De-Zhang, Lu Zhi-Wei, Zhao Yu-Jun, Yang Xiao-Bao","doi":"10.7498/aps.72.20230106","DOIUrl":"https://doi.org/10.7498/aps.72.20230106","url":null,"abstract":"The stochastic dynamics of spin semiclassical system at finite temperature is usually described by stochastic Landau-Lifshitz equation. In this work, the stochastic differential equation for spin semiclassical system is studied. The generalized formulation of effective Langevin equation and the corresponding Fokker-Planck equation are derived. The obtained effective Langevin equation offers an accurate description of the distribution in the canonical ensemble for spin semiclassical system. When the damping term and the stochastic term vanish, the effective Langevin equation reduces to the semiclassical equation of motion for spin system. Hence, the effective Langevin equation can be seen as a generalization of the stochastic Landau-Lifshitz equation. The explicit expressions for the effective Langevin equation and the corresponding Fokker-Planck equation are shown in both Cartesian and Spherical coordinates. It is demonstrated that, the longitudinal effect can be easily illustrated from the expressions in Spherical coordinates. The effective Langevin equation is applied to the simple system of a single spin in a constant magnetic field. In choosing an appropriate form, the Langevin equation can be easily solved and the stationary Boltzmann distribution can be obtained. The correctness of the Langevin approach to the spin semiclassical system is thus confirmed.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"22 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81501989","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Shuai Han, Qiubo Guo, Yaxiang Lu, Liquan Chen, Yong-Sheng Hu
Aqueous alkali-metal-ion batteries are a popular frontier research area, expected to apply for large-scale energy storage due to their high safety, low cost, and environmental friendliness. Depending on diversified social development, batteries ought to function in various ambient, including polar regions and high-altitude locales. Delivering excellent electrochemical performance at low temperatures is crucial to develop aqueous alkali-metal-ion batteries. This review summarizes the representative research progress in the field of aqueous low-temperature alkali-metal-ion batteries in recent years,based on the subjects of electrolyte, electrode, and interface. Firstly, we discussed the challenges of aqueous alkali-metal-ion batteries operated at low temperatures and the corresponding failure mechanisms. At subzero temperatures, aqueous alkali-metal-ion batteries couldn't work or exhibit little capacity, arising from the frozen electrolytes, electrode materials with slow kinetics, and huge interface impedances, which seriously limits their wide application in low-temperature conditions. Then, combined with the latest research work, various strategies have been investigated to improve the electrochemical performance of batteries at low temperatures. To date, the strategies for reducing the freezing point of electrolytes have primarily focused on breaking H-bonds between free water molecules by increasing salt concentration, adding organic/inorganic additives, and using hydrogel as electrolytes. In terms of electrodes, the related studies have concentrated on regulating the structure and morphology of electrodes, introducing the dual ion battery mechanism, and using organic materials and Zn electrodes to alleviate the slow ion dynamics of electrodes. In addition, adding appropriate organic solvents that can generate protective layers with low interface impedance on the electrode surface in the electrolyte can also improve the low-temperature performance of aqueous alkali-metal-ion batteries. Finally, we evaluated multi-dimensionally all strategies, expected to provide a comprehensive reference and point out the direction for the further improvement and practical application of the aqueous alkali-metal-ion batteries at low temperatures.
{"title":"Recent Progress in Aqueous Alkali-metal-ion batteries at low temperatures","authors":"Shuai Han, Qiubo Guo, Yaxiang Lu, Liquan Chen, Yong-Sheng Hu","doi":"10.7498/aps.72.20230024","DOIUrl":"https://doi.org/10.7498/aps.72.20230024","url":null,"abstract":"Aqueous alkali-metal-ion batteries are a popular frontier research area, expected to apply for large-scale energy storage due to their high safety, low cost, and environmental friendliness. Depending on diversified social development, batteries ought to function in various ambient, including polar regions and high-altitude locales. Delivering excellent electrochemical performance at low temperatures is crucial to develop aqueous alkali-metal-ion batteries. This review summarizes the representative research progress in the field of aqueous low-temperature alkali-metal-ion batteries in recent years,based on the subjects of electrolyte, electrode, and interface. Firstly, we discussed the challenges of aqueous alkali-metal-ion batteries operated at low temperatures and the corresponding failure mechanisms. At subzero temperatures, aqueous alkali-metal-ion batteries couldn't work or exhibit little capacity, arising from the frozen electrolytes, electrode materials with slow kinetics, and huge interface impedances, which seriously limits their wide application in low-temperature conditions. Then, combined with the latest research work, various strategies have been investigated to improve the electrochemical performance of batteries at low temperatures. To date, the strategies for reducing the freezing point of electrolytes have primarily focused on breaking H-bonds between free water molecules by increasing salt concentration, adding organic/inorganic additives, and using hydrogel as electrolytes. In terms of electrodes, the related studies have concentrated on regulating the structure and morphology of electrodes, introducing the dual ion battery mechanism, and using organic materials and Zn electrodes to alleviate the slow ion dynamics of electrodes. In addition, adding appropriate organic solvents that can generate protective layers with low interface impedance on the electrode surface in the electrolyte can also improve the low-temperature performance of aqueous alkali-metal-ion batteries. Finally, we evaluated multi-dimensionally all strategies, expected to provide a comprehensive reference and point out the direction for the further improvement and practical application of the aqueous alkali-metal-ion batteries at low temperatures.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"13 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81723624","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Reservoir computing (RC) is a simplified recurrent neural network, can be implemented by using a nonlinear system with delay feedback, called as delay-based RC. Various nonlinear nodes and feedback loop structures are proposed. Most works are based on the dynamical responses in intensity of the nonlinear systems. There are also a photoelectric RC system based on wavelength dynamics and an all-optical RC based on the phase dynamics of a semiconductor laser with optical feedback, as well as so-called polarization dynamics of a vertical cavity surface emitting laser (VCSEL). However, these VCSEL-RCs actually are based on the intensity dynamics of two mutually orthogonal polarization modes, or polarization-resolved intensity dynamics. The RC based on rich dynamical responses in polarization has not yet been seen. A semiconductor optical amplifier (SOA) fiber ring laser can produce rich dynamical states in polarization, is used in optical chaotic secure communication and distributed optical fiber sensing. To further expand the application of polarization dynamics of the SOA fiber ring laser and open up a new direction for the research of optical RC neural network, an all-optical RC system based on polarization dynamics of the ring laser is proposed. The ring laser is used as the reservoir, and the SOA as the nonlinear node. After the input signal is masked according to a synchronization scheme, it is injected into the reservoir by intensity modulation for a continuous wave generated by a super-luminescent light emitting diode (SLED). The dynamical response in polarization of the ring laser is detected by a polarizer and a photodetector. The influences of the SOA operation current, output power of the SLED and attenuation of a variable optical attenuator (VOA) in the fiber loop on the polarization dynamic characteristic, mainly refers to the output degree of polarization, of the laser are analyzed experimentally. The fading memory abilities and nonlinear responses of the RC system based on the polarization dynamic response and intensity dynamic response are compared in experiment. The influences of output power of the SLED and attenuation of the VOA on fading memory ability, consistency and separation of the RC system based on the two kinds of dynamic responses are investigated experimentally. Thus the range of the VOA attenuation is determined. The network performance of the polarization dynamics RC system is evaluated by processing the Santa Fe time series prediction task and the multi-waveform recognition task. The prediction error can be as low as 0.0058 for the time series prediction task, and the accuracy can be as high as 100% for the recognition task under the appropriate system parameters and only 30 virtual nodes. The experimental results show that the polarization dynamics RC system has good prediction performance and classification ability, which are comparable to the existing intensity dynamics RC system based on the ring laser. The system
{"title":"All-optical reservoir computing system based on polarization dynamics","authors":"Fang Nian, Qian Ruolan, Wang Shuai","doi":"10.7498/aps.72.20230722","DOIUrl":"https://doi.org/10.7498/aps.72.20230722","url":null,"abstract":"Reservoir computing (RC) is a simplified recurrent neural network, can be implemented by using a nonlinear system with delay feedback, called as delay-based RC. Various nonlinear nodes and feedback loop structures are proposed. Most works are based on the dynamical responses in intensity of the nonlinear systems. There are also a photoelectric RC system based on wavelength dynamics and an all-optical RC based on the phase dynamics of a semiconductor laser with optical feedback, as well as so-called polarization dynamics of a vertical cavity surface emitting laser (VCSEL). However, these VCSEL-RCs actually are based on the intensity dynamics of two mutually orthogonal polarization modes, or polarization-resolved intensity dynamics. The RC based on rich dynamical responses in polarization has not yet been seen. A semiconductor optical amplifier (SOA) fiber ring laser can produce rich dynamical states in polarization, is used in optical chaotic secure communication and distributed optical fiber sensing. To further expand the application of polarization dynamics of the SOA fiber ring laser and open up a new direction for the research of optical RC neural network, an all-optical RC system based on polarization dynamics of the ring laser is proposed. The ring laser is used as the reservoir, and the SOA as the nonlinear node. After the input signal is masked according to a synchronization scheme, it is injected into the reservoir by intensity modulation for a continuous wave generated by a super-luminescent light emitting diode (SLED). The dynamical response in polarization of the ring laser is detected by a polarizer and a photodetector. The influences of the SOA operation current, output power of the SLED and attenuation of a variable optical attenuator (VOA) in the fiber loop on the polarization dynamic characteristic, mainly refers to the output degree of polarization, of the laser are analyzed experimentally. The fading memory abilities and nonlinear responses of the RC system based on the polarization dynamic response and intensity dynamic response are compared in experiment. The influences of output power of the SLED and attenuation of the VOA on fading memory ability, consistency and separation of the RC system based on the two kinds of dynamic responses are investigated experimentally. Thus the range of the VOA attenuation is determined. The network performance of the polarization dynamics RC system is evaluated by processing the Santa Fe time series prediction task and the multi-waveform recognition task. The prediction error can be as low as 0.0058 for the time series prediction task, and the accuracy can be as high as 100% for the recognition task under the appropriate system parameters and only 30 virtual nodes. The experimental results show that the polarization dynamics RC system has good prediction performance and classification ability, which are comparable to the existing intensity dynamics RC system based on the ring laser. The system","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"23 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85187686","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dirac quantum materials comprise a broad category of condensed matter systems characterized by low-energy excitations described by the Dirac equation. These excitations, which can manifest as either collective states or band structure effects, have been identified in a wide range of systems, from exotic quantum fluids to crystalline materials. Over the past several decades, they have sparked extensive experimental and theoretical investigations in various materials, such as topological insulators and topological semimetals. The study of Dirac quantum materials has also opened up new possibilities for topological quantum computing, giving rise to a burgeoning field of physics and offering a novel platform for realizing rich topological phases, including various quantum Hall effects and topological superconducting phases. Furthermore, the topologically non-trivial band structures of Dirac quantum materials give rise to plentiful intriguing transport phenomena, including longitudinal negative magnetoresistance, quantum interference effects, and helical magnetic effects, among others. Currently, numerous transport phenomena in Dirac quantum materials remain poorly understood from a theoretical standpoint, such as linear magnetoresistance in weak fields, anomalous Hall effects in nonmagnetic materials, and three-dimensional quantum Hall effects. Investigating these transport properties will not only deepen our understanding of Dirac quantum materials but also provide crucial insights for their potential applications in spintronics and quantum computing. This review provides a comprehensive overview of the quantum transport theory and quantum anomaly effects related to the Dirac equation, with a focus on massive Dirac fermions and quantum anomalous semimetals. Additionally, it offers insights into the realization of parity anomaly and half-quantized quantum Hall effects in semi-magnetic topological insulators. Lastly, the review discusses the key scientific questions of interest in the field of quantum transport theory.
{"title":"Recent progress of transport theory in Dirac quantum materials","authors":"Wang Huan-Wen, Fu Bo, Shen Shun-Qing","doi":"10.7498/aps.72.20230672","DOIUrl":"https://doi.org/10.7498/aps.72.20230672","url":null,"abstract":"Dirac quantum materials comprise a broad category of condensed matter systems characterized by low-energy excitations described by the Dirac equation. These excitations, which can manifest as either collective states or band structure effects, have been identified in a wide range of systems, from exotic quantum fluids to crystalline materials. Over the past several decades, they have sparked extensive experimental and theoretical investigations in various materials, such as topological insulators and topological semimetals. The study of Dirac quantum materials has also opened up new possibilities for topological quantum computing, giving rise to a burgeoning field of physics and offering a novel platform for realizing rich topological phases, including various quantum Hall effects and topological superconducting phases. Furthermore, the topologically non-trivial band structures of Dirac quantum materials give rise to plentiful intriguing transport phenomena, including longitudinal negative magnetoresistance, quantum interference effects, and helical magnetic effects, among others. Currently, numerous transport phenomena in Dirac quantum materials remain poorly understood from a theoretical standpoint, such as linear magnetoresistance in weak fields, anomalous Hall effects in nonmagnetic materials, and three-dimensional quantum Hall effects. Investigating these transport properties will not only deepen our understanding of Dirac quantum materials but also provide crucial insights for their potential applications in spintronics and quantum computing. This review provides a comprehensive overview of the quantum transport theory and quantum anomaly effects related to the Dirac equation, with a focus on massive Dirac fermions and quantum anomalous semimetals. Additionally, it offers insights into the realization of parity anomaly and half-quantized quantum Hall effects in semi-magnetic topological insulators. Lastly, the review discusses the key scientific questions of interest in the field of quantum transport theory.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"64 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85208264","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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