It is shown that discharges with negative triangularity have lower turbulence induced transport and better energy confinement, so the tokamaks with negative triangularity are recognized as a better choice for future fusion devices. In order to explore the features of the energetic particle driven instabilities with negative triangularity, the kinetic- magnetohydrodynamic hybrid code M3D-K has been applied to investigate the linear instability and nonlinear evolution of the fishbone driven by energetic ions with different triangularity. Based on EAST like parameters, it is found that negative triangularity destabilizes the ideal internal kink mode, but stabilizes the fishbone instability. Nonlinear simulations show that the fishbone instability with negative triangularity is hard to saturate without fluid nonlinearity. The possible explanation is that the orbits of fast ions locate more centrally with negative triagularity, so the energy exchange between energetic ions and the fishbone is more efficient than that with positive triangularity. These simulation results demonstrate that considering the fishbone driven by energetic particles, the negative triangularity does not confer a obvious advantage over the positive triangularity.
{"title":"Numerical simulations of fishbones driven by fast ions in negative triangularity tokamak","authors":"Ren Zhen-Zhen, Shen Wei","doi":"10.7498/aps.72.20230650","DOIUrl":"https://doi.org/10.7498/aps.72.20230650","url":null,"abstract":"It is shown that discharges with negative triangularity have lower turbulence induced transport and better energy confinement, so the tokamaks with negative triangularity are recognized as a better choice for future fusion devices. In order to explore the features of the energetic particle driven instabilities with negative triangularity, the kinetic- magnetohydrodynamic hybrid code M3D-K has been applied to investigate the linear instability and nonlinear evolution of the fishbone driven by energetic ions with different triangularity. Based on EAST like parameters, it is found that negative triangularity destabilizes the ideal internal kink mode, but stabilizes the fishbone instability. Nonlinear simulations show that the fishbone instability with negative triangularity is hard to saturate without fluid nonlinearity. The possible explanation is that the orbits of fast ions locate more centrally with negative triagularity, so the energy exchange between energetic ions and the fishbone is more efficient than that with positive triangularity. These simulation results demonstrate that considering the fishbone driven by energetic particles, the negative triangularity does not confer a obvious advantage over the positive triangularity.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"5 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76887094","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}
Gao Wei, Yifan Luo, Xing Yu, Ding Peng, Chen Bin-Hui, Han Qing-Yan, Yan Xue-Wen, Zhang Cheng-Yun, Dong Jun
Building core-shell structures have been widely used to enhance and regulate the luminescence properties of rare-earth-doped micro/nano materials. In this work, a variety of different NaErF4 core-shell and core-shell-shell nanocrystals were successfully constructed based on high temperature co-precipitation method by epitaxial growth technology. The upconversion red emission intensity of Er3+ ions in different core-shell structures was effectively enhanced by regulating their structures and doping ions. The experimental structures show that the constructed core-shell nanocrystals are all hexagonal phase structure, and the size of the core-shell structure is about 40 nm. In the near infrared 980 nm laser excitation, the NaErF4 core-shell nanocrystals showed strong single-band red emission. And the single-band red emission intensity of Er3+ ions was enhanced through constructing the NaErF4@NaYbF4:2%Er3+ core-shell structures. The experimental results showed that red emission intensity of Er3+ ions was about 1.4 times higher than that of the NaErF4@NaYbF4 core-shell structures by constructing the NaErF4@NaYbF4:2%Er3+ core-shell structures under 980 nm excitation, and the red/green emission intensity ratio was increased from 5.4 to 6.5. Meanwhile, when NaErF4@NaYbF4:2%Er3+ core-shell structures have recoated the NaYF4 inert shell and introduced trace amounts of Tm3+ ions, the red emission intensity of Er3+ ions was 23.2 and 40.3 times compared with NaErF4@NaYbF4 core-shell structures, and the red/green emission intensity ratio reached 7.5 and 10.2, respectively. The red emssion enhancement of Er3+ ions was mainly caused by bidirectional energy transfer processes of high excitation energy of Yb3+ ions and energy trapping center of Tm3+ ions which effectively changed the densities of population of luminescent energy levels of Er3+ ions. What’s more, the coated NaYF4 inert shell also effectively reduced the surface quenching effect of nanocrystals. The mechanism of red enhancement in different core-shell structures were discussed based on the spectral properties, the processes of interion energy transfer and luminescence kinetics. The constructed NaErF4@NaYbF4:2%Er3+@NaYF4 core-shell structures with high-efficiency red emission in this work has great application potential in the fields of colorful anti-counterfeiting, display and biological imaging.
{"title":"Enhancing red upconversion emission of Er3+ by building NaErF4@NaYbF4:2%Er3+ core-shell structure","authors":"Gao Wei, Yifan Luo, Xing Yu, Ding Peng, Chen Bin-Hui, Han Qing-Yan, Yan Xue-Wen, Zhang Cheng-Yun, Dong Jun","doi":"10.7498/aps.72.20230762","DOIUrl":"https://doi.org/10.7498/aps.72.20230762","url":null,"abstract":"Building core-shell structures have been widely used to enhance and regulate the luminescence properties of rare-earth-doped micro/nano materials. In this work, a variety of different NaErF<sub>4</sub> core-shell and core-shell-shell nanocrystals were successfully constructed based on high temperature co-precipitation method by epitaxial growth technology. The upconversion red emission intensity of Er<sup>3+</sup> ions in different core-shell structures was effectively enhanced by regulating their structures and doping ions. The experimental structures show that the constructed core-shell nanocrystals are all hexagonal phase structure, and the size of the core-shell structure is about 40 nm. In the near infrared 980 nm laser excitation, the NaErF<sub>4</sub> core-shell nanocrystals showed strong single-band red emission. And the single-band red emission intensity of Er<sup>3+</sup> ions was enhanced through constructing the NaErF<sub>4</sub>@NaYbF<sub>4</sub>:2%Er<sup>3+</sup> core-shell structures. The experimental results showed that red emission intensity of Er<sup>3+</sup> ions was about 1.4 times higher than that of the NaErF<sub>4</sub>@NaYbF<sub>4</sub> core-shell structures by constructing the NaErF<sub>4</sub>@NaYbF<sub>4</sub>:2%Er<sup>3+</sup> core-shell structures under 980 nm excitation, and the red/green emission intensity ratio was increased from 5.4 to 6.5. Meanwhile, when NaErF<sub>4</sub>@NaYbF<sub>4</sub>:2%Er<sup>3+</sup> core-shell structures have recoated the NaYF<sub>4</sub> inert shell and introduced trace amounts of Tm<sup>3+</sup> ions, the red emission intensity of Er<sup>3+</sup> ions was 23.2 and 40.3 times compared with NaErF<sub>4</sub>@NaYbF<sub>4</sub> core-shell structures, and the red/green emission intensity ratio reached 7.5 and 10.2, respectively. The red emssion enhancement of Er<sup>3+</sup> ions was mainly caused by bidirectional energy transfer processes of high excitation energy of Yb<sup>3+</sup> ions and energy trapping center of Tm<sup>3+</sup> ions which effectively changed the densities of population of luminescent energy levels of Er<sup>3+</sup> ions. What’s more, the coated NaYF<sub>4</sub> inert shell also effectively reduced the surface quenching effect of nanocrystals. The mechanism of red enhancement in different core-shell structures were discussed based on the spectral properties, the processes of interion energy transfer and luminescence kinetics. The constructed NaErF<sub>4</sub>@NaYbF<sub>4</sub>:2%Er<sup>3+</sup>@NaYF<sub>4</sub> core-shell structures with high-efficiency red emission in this work has great application potential in the fields of colorful anti-counterfeiting, display and biological imaging.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"56 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76909564","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}
Huang Zhi-Qiu, Zhang Meng, Peng Zhi-Min, Wang Zhen, Yang Qian-suo
Using numerical simulation and a constructed cavity ring-down spectroscopy device, the influence of the finite coherence of the injected laser on the coupling process between the injected light and the cavity longitudinal mode was studied. The finite coherence of the injected light leads to the randomness of the coupling pulse during frequency scanning. The randomness is mainly reflected in two aspects: Firstly, as the coherence length decreases, the random amplitude range of the coupling pulse increases. Secondly, as the coherence of the injected light deteriorates, the coupling pulse changes from a single pulse with intensity evolution to continuous multiple pulses, and the overall width gradually increases with the decrease of the scanning rate. Moreover, with the deterioration of the coherence, when the light intensity of the cavity is used to turn off the injected light, the decrease in the scanning rate can cause more than one injection shut-off and ring-down event in a frequency coupling process, especially when scanning with the length of the cavity. In addition, a theoretical method is proposed to estimate the ring-down time using the strength integral of different time intervals, and the relevant experimental verification is carried out. The experimental results show that the relative error of the ring-down time obtained by the intensity integration method is smaller than that obtained by the traditional fitting method.
{"title":"The influence of the finite coherence of injected light on the ring-down cavity measurement method and the intensity integral method for the ring-down time determination","authors":"Huang Zhi-Qiu, Zhang Meng, Peng Zhi-Min, Wang Zhen, Yang Qian-suo","doi":"10.7498/aps.72.20230448","DOIUrl":"https://doi.org/10.7498/aps.72.20230448","url":null,"abstract":"Using numerical simulation and a constructed cavity ring-down spectroscopy device, the influence of the finite coherence of the injected laser on the coupling process between the injected light and the cavity longitudinal mode was studied. The finite coherence of the injected light leads to the randomness of the coupling pulse during frequency scanning. The randomness is mainly reflected in two aspects: Firstly, as the coherence length decreases, the random amplitude range of the coupling pulse increases. Secondly, as the coherence of the injected light deteriorates, the coupling pulse changes from a single pulse with intensity evolution to continuous multiple pulses, and the overall width gradually increases with the decrease of the scanning rate. Moreover, with the deterioration of the coherence, when the light intensity of the cavity is used to turn off the injected light, the decrease in the scanning rate can cause more than one injection shut-off and ring-down event in a frequency coupling process, especially when scanning with the length of the cavity. In addition, a theoretical method is proposed to estimate the ring-down time using the strength integral of different time intervals, and the relevant experimental verification is carried out. The experimental results show that the relative error of the ring-down time obtained by the intensity integration method is smaller than that obtained by the traditional fitting method.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"21 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77210397","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}
Nong Jie, Zhang Yi-Yi, Wei Xue-Ling, Jiang Xin-Peng, Li Ning, Wang Dong-Ying, Xiao Si-Yang, Chen Hong-Ting, Zhang Zhen-Rong, Yang Jun-Bo
The "cat's eye effect" in the optical window of all kinds of photoelectric equipment is the main basis of a laser active detection system, which poses a great threat to military equipment and combatants. However, under the condition of ensuring high visible transmittance, the sniper stealth scheme for anti-laser active detection remains to be discussed. In this paper, genetic algorithm was used to reverse design the metasurface anti-reflection film. Si3N4 and Ag were composed of three-layer anti-reflection film, and rectangular array of metal micro-nano structures were added on the top layer to form a wavelength selective absorber, so as to achieve the effect of low reflection and high absorption at laser wavelength. By combining the device design with genetic algorithm, the parameter combination that best meets the target performance of the device is obtained. The average transmittance at 380nm~780nm is 88% meanwhile the maximum transmittance peak of 94%. The reflectance at 1550nm of 10%, and the absorption rate of 80% are achieved. In order to better meet the requirements of practical application, we further designed the cross metal array to obtain polarization insensitive characteristics. The metasurface anti-reflective membrane with improved structure can achieve an average visible transmittance of 82% and a reflectance of 5% at 1550nm. The two metasurface anti-reflection film designed in this paper does not require additional devices, and the imaging quality can be guaranteed. At the same time, it can effectively reduce the laser echo energy, so as to achieve the effect of high quality visible light transmittance and laser stealth compatibility.
{"title":"Research on Dielectric/Metal/Dielectric film system for high transmittance compatible laser stealth","authors":"Nong Jie, Zhang Yi-Yi, Wei Xue-Ling, Jiang Xin-Peng, Li Ning, Wang Dong-Ying, Xiao Si-Yang, Chen Hong-Ting, Zhang Zhen-Rong, Yang Jun-Bo","doi":"10.7498/aps.72.20230855","DOIUrl":"https://doi.org/10.7498/aps.72.20230855","url":null,"abstract":"The \"cat's eye effect\" in the optical window of all kinds of photoelectric equipment is the main basis of a laser active detection system, which poses a great threat to military equipment and combatants. However, under the condition of ensuring high visible transmittance, the sniper stealth scheme for anti-laser active detection remains to be discussed. In this paper, genetic algorithm was used to reverse design the metasurface anti-reflection film. Si3N4 and Ag were composed of three-layer anti-reflection film, and rectangular array of metal micro-nano structures were added on the top layer to form a wavelength selective absorber, so as to achieve the effect of low reflection and high absorption at laser wavelength. By combining the device design with genetic algorithm, the parameter combination that best meets the target performance of the device is obtained. The average transmittance at 380nm~780nm is 88% meanwhile the maximum transmittance peak of 94%. The reflectance at 1550nm of 10%, and the absorption rate of 80% are achieved. In order to better meet the requirements of practical application, we further designed the cross metal array to obtain polarization insensitive characteristics. The metasurface anti-reflective membrane with improved structure can achieve an average visible transmittance of 82% and a reflectance of 5% at 1550nm. The two metasurface anti-reflection film designed in this paper does not require additional devices, and the imaging quality can be guaranteed. At the same time, it can effectively reduce the laser echo energy, so as to achieve the effect of high quality visible light transmittance and laser stealth compatibility.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"580 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76259113","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}
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}
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