Pub Date : 2024-09-06DOI: 10.1038/s42005-024-01790-8
Adrian Skasberg Aasen, Andras Di Giovanni, Hannes Rotzinger, Alexey V. Ustinov, Martin Gärttner
Quantum technologies rely heavily on accurate control and reliable readout of quantum systems. Current experiments are limited by numerous sources of noise that can only be partially captured by simple analytical models and additional characterization of the noise sources is required. We test the ability of readout error mitigation to correct noise found in systems composed of quantum two-level objects (qubits). To probe the limit of such methods, we designed a beyond-classical readout error mitigation protocol based on quantum state tomography (QST), which estimates the density matrix of a quantum system, and quantum detector tomography (QDT), which characterizes the measurement procedure. By treating readout error mitigation in the context of state tomography the method becomes largely readout mode-, architecture-, noise source-, and quantum state-independent. We implement this method on a superconducting qubit and evaluate the increase in reconstruction fidelity for QST. We characterize the performance of the method by varying important noise sources, such as suboptimal readout signal amplification, insufficient resonator photon population, off-resonant qubit drive, and effectively shortened T1 and T2 coherence. As a result, we identified noise sources for which readout error mitigation worked well, and observed decreases in readout infidelity by a factor of up to 30. Significant efforts have been dedicated to mitigate gate errors in quantum devices, while comparatively little attention has been given to the increasing issue of readout errors. The authors present an explicit protocol for comprehensive readout error mitigation with quantum state tomography, and demonstrate its applicability experimentally on a superconducting qubit device.
{"title":"Readout error mitigated quantum state tomography tested on superconducting qubits","authors":"Adrian Skasberg Aasen, Andras Di Giovanni, Hannes Rotzinger, Alexey V. Ustinov, Martin Gärttner","doi":"10.1038/s42005-024-01790-8","DOIUrl":"10.1038/s42005-024-01790-8","url":null,"abstract":"Quantum technologies rely heavily on accurate control and reliable readout of quantum systems. Current experiments are limited by numerous sources of noise that can only be partially captured by simple analytical models and additional characterization of the noise sources is required. We test the ability of readout error mitigation to correct noise found in systems composed of quantum two-level objects (qubits). To probe the limit of such methods, we designed a beyond-classical readout error mitigation protocol based on quantum state tomography (QST), which estimates the density matrix of a quantum system, and quantum detector tomography (QDT), which characterizes the measurement procedure. By treating readout error mitigation in the context of state tomography the method becomes largely readout mode-, architecture-, noise source-, and quantum state-independent. We implement this method on a superconducting qubit and evaluate the increase in reconstruction fidelity for QST. We characterize the performance of the method by varying important noise sources, such as suboptimal readout signal amplification, insufficient resonator photon population, off-resonant qubit drive, and effectively shortened T1 and T2 coherence. As a result, we identified noise sources for which readout error mitigation worked well, and observed decreases in readout infidelity by a factor of up to 30. Significant efforts have been dedicated to mitigate gate errors in quantum devices, while comparatively little attention has been given to the increasing issue of readout errors. The authors present an explicit protocol for comprehensive readout error mitigation with quantum state tomography, and demonstrate its applicability experimentally on a superconducting qubit device.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01790-8.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142182134","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-06DOI: 10.1038/s42005-024-01714-6
Giulio Tani Raffaelli, Margherita Lalli, Francesca Tria
Urn models for innovation capture fundamental empirical laws shared by several real-world processes. The so-called urn model with triggering includes, as particular cases, the urn representation of the two-parameter Poisson-Dirichlet process and the Dirichlet process, seminal in Bayesian non-parametric inference. In this work, we leverage this connection to introduce a general approach for quantifying closeness between symbolic sequences and test it within the framework of the authorship attribution problem. The method demonstrates high accuracy when compared to other related methods in different scenarios, featuring a substantial gain in computational efficiency and theoretical transparency. Beyond the practical convenience, this work demonstrates how the recently established connection between urn models and non-parametric Bayesian inference can pave the way for designing more efficient inference methods. In particular, the hybrid approach that we propose allows us to relax the exchangeability hypothesis, which can be particularly relevant for systems exhibiting complex correlation patterns and non-stationary dynamics. A class of urn-based models accounts for stochastic regularities observed in systems that exhibit innovation in diverse forms and temporal scales, from the appearance of new organisms to the evolution of language to daily new experiences. The authors investigate the predictive power of those models in inference problems, addressing the authorship attribution task as a case study.
{"title":"Inference through innovation processes tested in the authorship attribution task","authors":"Giulio Tani Raffaelli, Margherita Lalli, Francesca Tria","doi":"10.1038/s42005-024-01714-6","DOIUrl":"10.1038/s42005-024-01714-6","url":null,"abstract":"Urn models for innovation capture fundamental empirical laws shared by several real-world processes. The so-called urn model with triggering includes, as particular cases, the urn representation of the two-parameter Poisson-Dirichlet process and the Dirichlet process, seminal in Bayesian non-parametric inference. In this work, we leverage this connection to introduce a general approach for quantifying closeness between symbolic sequences and test it within the framework of the authorship attribution problem. The method demonstrates high accuracy when compared to other related methods in different scenarios, featuring a substantial gain in computational efficiency and theoretical transparency. Beyond the practical convenience, this work demonstrates how the recently established connection between urn models and non-parametric Bayesian inference can pave the way for designing more efficient inference methods. In particular, the hybrid approach that we propose allows us to relax the exchangeability hypothesis, which can be particularly relevant for systems exhibiting complex correlation patterns and non-stationary dynamics. A class of urn-based models accounts for stochastic regularities observed in systems that exhibit innovation in diverse forms and temporal scales, from the appearance of new organisms to the evolution of language to daily new experiences. The authors investigate the predictive power of those models in inference problems, addressing the authorship attribution task as a case study.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01714-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142182132","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-06DOI: 10.1038/s42005-024-01792-6
K. V. S. Chaithanya, Aleksandra Ardaševa, Oliver J. Meacock, William M. Durham, Sumesh P. Thampi, Amin Doostmohammadi
Collectively moving cellular systems often contain a proportion of dead cells or non-motile genotypes. When mixed, nematically aligning motile and non-motile agents are known to segregate spontaneously. However, the role that topological defects and active stresses play in shaping the distribution of the two phases remains unresolved. In this study, we investigate the behaviour of a two-dimensional binary mixture of active and passive nematic fluids to understand how topological defects are transported between the two phases and, ultimately, how this leads to the segregation of topological charges. When the activity of the motile phase is large, and the tension at the interface of motile and non-motile phases is weak, we find that the active phase tends to accumulate +1/2 defects and expel −1/2 defects so that the motile phase develops a net positive charge. Conversely, when the activity of the motile phase is comparatively small and interfacial tension is strong, the opposite occurs so that the active phase develops a net negative charge. We then use these simulations to develop a physical intuition of the underlying processes that drive the charge segregation. Lastly, we quantify the sensitivity of this process on the other model parameters, by exploring the effect that anchoring strength, orientational elasticity, friction, and volume fraction of the motile phase have on topological charge segregation. As +1/2 and −1/2 defects have very different effects on interface morphology and fluid transport, this study offers new insights into the spontaneous pattern formation that occurs when motile and non-motile cells interact. Collectively moving cellular systems often contain both motile and non-motile genotypes, and when mixed, these agents segregate spontaneously. The study reveals that the segregation of topological charges between these agents depends on activity and interfacial tension, with high activity and low tension favoring a positively charged motile phase.
{"title":"Transport of topological defects in a biphasic mixture of active and passive nematic fluids","authors":"K. V. S. Chaithanya, Aleksandra Ardaševa, Oliver J. Meacock, William M. Durham, Sumesh P. Thampi, Amin Doostmohammadi","doi":"10.1038/s42005-024-01792-6","DOIUrl":"10.1038/s42005-024-01792-6","url":null,"abstract":"Collectively moving cellular systems often contain a proportion of dead cells or non-motile genotypes. When mixed, nematically aligning motile and non-motile agents are known to segregate spontaneously. However, the role that topological defects and active stresses play in shaping the distribution of the two phases remains unresolved. In this study, we investigate the behaviour of a two-dimensional binary mixture of active and passive nematic fluids to understand how topological defects are transported between the two phases and, ultimately, how this leads to the segregation of topological charges. When the activity of the motile phase is large, and the tension at the interface of motile and non-motile phases is weak, we find that the active phase tends to accumulate +1/2 defects and expel −1/2 defects so that the motile phase develops a net positive charge. Conversely, when the activity of the motile phase is comparatively small and interfacial tension is strong, the opposite occurs so that the active phase develops a net negative charge. We then use these simulations to develop a physical intuition of the underlying processes that drive the charge segregation. Lastly, we quantify the sensitivity of this process on the other model parameters, by exploring the effect that anchoring strength, orientational elasticity, friction, and volume fraction of the motile phase have on topological charge segregation. As +1/2 and −1/2 defects have very different effects on interface morphology and fluid transport, this study offers new insights into the spontaneous pattern formation that occurs when motile and non-motile cells interact. Collectively moving cellular systems often contain both motile and non-motile genotypes, and when mixed, these agents segregate spontaneously. The study reveals that the segregation of topological charges between these agents depends on activity and interfacial tension, with high activity and low tension favoring a positively charged motile phase.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-09-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01792-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142182133","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-05DOI: 10.1038/s42005-024-01777-5
Na Sun, Weixuan Zhang, Hao Yuan, Xiangdong Zhang
Bound states in the continuum (BICs), referring to spatially localized bound states with energies falling within the range of extended modes, have been extensively investigated in single-particle systems, leading to diverse applications in photonics, acoustics, and other classical-wave systems. Recently, there has been theoretical interest in exploring many-body BICs in interacting quantum systems, which necessitate the careful design of impurity potentials or spatial profiles of interaction. Here, we propose a type of many-body BICs localized at boundaries, which can be purely induced by the uniform onsite interaction without requiring any specific design of impurity potential or nonlocal interaction. We numerically show that three or more interacting bosons can concentrate on the boundary of a homogeneous one-dimensional lattice, which is absent at single- and two-particle counterparts. Moreover, the eigenenergy of multi-boson bound states can embed within the continuous energy spectra of extended scattering states, thereby giving rise to interaction-induced boundary many-body BICs. Furthermore, by mapping Fock states of three and four bosons to nonlinear circuit networks, we experimentally simulate boundary many-body BICs. Our findings enrich the comprehension of correlated BICs beyond the single-particle level, and have the potential to inspire future investigations on exploring many-body BICs. Bound states in the continuum (BICs) have been extensively investigated in single-particle systems, leading to diverse applications in photonics, acoustics, and other classical-wave systems. Here, the authors propose a type of interaction-induced many-body BICs at boundaries and experimentally simulate these boundary many-body BICs using nonlinear circuit networks.
{"title":"Boundary-localized many-body bound states in the continuum","authors":"Na Sun, Weixuan Zhang, Hao Yuan, Xiangdong Zhang","doi":"10.1038/s42005-024-01777-5","DOIUrl":"10.1038/s42005-024-01777-5","url":null,"abstract":"Bound states in the continuum (BICs), referring to spatially localized bound states with energies falling within the range of extended modes, have been extensively investigated in single-particle systems, leading to diverse applications in photonics, acoustics, and other classical-wave systems. Recently, there has been theoretical interest in exploring many-body BICs in interacting quantum systems, which necessitate the careful design of impurity potentials or spatial profiles of interaction. Here, we propose a type of many-body BICs localized at boundaries, which can be purely induced by the uniform onsite interaction without requiring any specific design of impurity potential or nonlocal interaction. We numerically show that three or more interacting bosons can concentrate on the boundary of a homogeneous one-dimensional lattice, which is absent at single- and two-particle counterparts. Moreover, the eigenenergy of multi-boson bound states can embed within the continuous energy spectra of extended scattering states, thereby giving rise to interaction-induced boundary many-body BICs. Furthermore, by mapping Fock states of three and four bosons to nonlinear circuit networks, we experimentally simulate boundary many-body BICs. Our findings enrich the comprehension of correlated BICs beyond the single-particle level, and have the potential to inspire future investigations on exploring many-body BICs. Bound states in the continuum (BICs) have been extensively investigated in single-particle systems, leading to diverse applications in photonics, acoustics, and other classical-wave systems. Here, the authors propose a type of interaction-induced many-body BICs at boundaries and experimentally simulate these boundary many-body BICs using nonlinear circuit networks.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01777-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142137880","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-04DOI: 10.1038/s42005-024-01789-1
Riyi Zheng, Jing Lin, Jialuo Liang, Kun Ding, Jiuyang Lu, Weiyin Deng, Manzhu Ke, Xueqin Huang, Zhengyou Liu
The gap in spectra of a physical system is fundamental in physics, while gap topology further restricts possible occurrent gaps of topological boundary states. The emergence of non-Hermiticity unveils a unique gap type known as the point gap, which forecasts the wavefunction localization, known as the non-Hermitian skin effect. Therefore, experimentally identifying the point gap in the complex frequency plane through a real operating frequency can become a tool for the systematic investigation of skin effects. Here, we utilize a Weyl phononic crystal to demonstrate that the point gap constituted by bulk and Fermi-arc surface states can be observed experimentally by a real-space field mapping technique. The identified point gaps forecast various skin effects and their evolutions. We further experimentally demonstrate the hinge skin effect in a parallelogram structure. Our work provides a feasible recipe to explore point gap topology experimentally in a variety of systems and certainly stimulates the research on skin effects in three-dimensional systems. Point gap is signature of non-Hermitian systems, but the experimental identification of nontrivial point gaps is elusive. Here, the authors use a Weyl phononic crystal to demonstrate that the point gap constituted by bulk and Fermi-arc surface states can be observed experimentally by a real-space field mapping technique and discover various skin effects and their evolutions.
{"title":"Experimental probe of point gap topology from non-Hermitian Fermi-arcs","authors":"Riyi Zheng, Jing Lin, Jialuo Liang, Kun Ding, Jiuyang Lu, Weiyin Deng, Manzhu Ke, Xueqin Huang, Zhengyou Liu","doi":"10.1038/s42005-024-01789-1","DOIUrl":"10.1038/s42005-024-01789-1","url":null,"abstract":"The gap in spectra of a physical system is fundamental in physics, while gap topology further restricts possible occurrent gaps of topological boundary states. The emergence of non-Hermiticity unveils a unique gap type known as the point gap, which forecasts the wavefunction localization, known as the non-Hermitian skin effect. Therefore, experimentally identifying the point gap in the complex frequency plane through a real operating frequency can become a tool for the systematic investigation of skin effects. Here, we utilize a Weyl phononic crystal to demonstrate that the point gap constituted by bulk and Fermi-arc surface states can be observed experimentally by a real-space field mapping technique. The identified point gaps forecast various skin effects and their evolutions. We further experimentally demonstrate the hinge skin effect in a parallelogram structure. Our work provides a feasible recipe to explore point gap topology experimentally in a variety of systems and certainly stimulates the research on skin effects in three-dimensional systems. Point gap is signature of non-Hermitian systems, but the experimental identification of nontrivial point gaps is elusive. Here, the authors use a Weyl phononic crystal to demonstrate that the point gap constituted by bulk and Fermi-arc surface states can be observed experimentally by a real-space field mapping technique and discover various skin effects and their evolutions.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01789-1.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142130458","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-03DOI: 10.1038/s42005-024-01776-6
Paweł Ordyna, Carsten Bähtz, Erik Brambrink, Michael Bussmann, Alejandro Laso Garcia, Marco Garten, Lennart Gaus, Sebastian Göde, Jörg Grenzer, Christian Gutt, Hauke Höppner, Lingen Huang, Uwe Hübner, Oliver Humphries, Brian Edward Marré, Josefine Metzkes-Ng, Thomas Miethlinger, Motoaki Nakatsutsumi, Özgül Öztürk, Xiayun Pan, Franziska Paschke-Brühl, Alexander Pelka, Irene Prencipe, Thomas R. Preston, Lisa Randolph, Hans-Peter Schlenvoigt, Jan-Patrick Schwinkendorf, Michal Šmíd, Sebastian Starke, Radka Štefaníková, Erik Thiessenhusen, Toma Toncian, Karl Zeil, Ulrich Schramm, Thomas E. Cowan, Thomas Kluge
Ultra-intense lasers that ionize atoms and accelerate electrons in solids to near the speed of light can lead to kinetic instabilities that alter the laser absorption and subsequent electron transport, isochoric heating, and ion acceleration. These instabilities can be difficult to characterize, but X-ray scattering at keV photon energies allows for their visualization with femtosecond temporal resolution on the few nanometer mesoscale. Here, we perform such experiment on laser-driven flat silicon membranes that shows the development of structure with a dominant scale of 60 nm in the plane of the laser axis and laser polarization, and 95 nm in the vertical direction with a growth rate faster than 0.1 fs−1. Combining the XFEL experiments with simulations provides a complete picture of the structural evolution of ultra-fast laser-induced plasma density development, indicating the excitation of plasmons and a filamentation instability. Particle-in-cell simulations confirm that these signals are due to an oblique two-stream filamentation instability. These findings provide new insight into ultra-fast instability and heating processes in solids under extreme conditions at the nanometer level with possible implications for laser particle acceleration, inertial confinement fusion, and laboratory astrophysics. Ultrafast relativistic plasma instabilities accompany and influence laser matter interactions that accelerate particlebeams with potential applications in e.g radiotherapy or fussion fast ignition scenarios. Here, the authors use Small Angle X-ray Scattering to observe such instabilities on a femtosecond, tens of nanometer scale in solids, and draw conclusions on the underlying plasma dynamics.
超强激光可将固体中的原子电离和电子加速到接近光速，从而导致动力学不稳定性，改变激光吸收和随后的电子传输、等速加热和离子加速。这些不稳定性可能难以表征，但在 keV 光子能量下的 X 射线散射可以在几纳米的中尺度上以飞秒级的时间分辨率将其可视化。在这里，我们在激光驱动的平面硅膜上进行了这样的实验，结果表明，在激光轴和激光偏振平面上，结构的主要尺度为 60 纳米，在垂直方向上为 95 纳米，其增长速度快于 0.1 fs-1。将 XFEL 实验与模拟相结合，可以全面了解超快激光诱导等离子体密度发展的结构演变，表明等离子体的激发和丝状不稳定性。粒子间模拟证实，这些信号是由斜双流丝状不稳定性引起的。这些发现为纳米级极端条件下固体中的超快不稳定性和加热过程提供了新的视角，可能对激光粒子加速、惯性约束聚变和实验室天体物理学产生影响。超快相对论等离子体不稳定性伴随并影响着激光物质相互作用，从而加速粒子束，并有可能应用于放射治疗或冲击快速点火等场景。在这里，作者利用小角 X 射线散射观测了固体中飞秒级、数十纳米级的不稳定性，并得出了有关潜在等离子体动力学的结论。
{"title":"Visualizing plasmons and ultrafast kinetic instabilities in laser-driven solids using X-ray scattering","authors":"Paweł Ordyna, Carsten Bähtz, Erik Brambrink, Michael Bussmann, Alejandro Laso Garcia, Marco Garten, Lennart Gaus, Sebastian Göde, Jörg Grenzer, Christian Gutt, Hauke Höppner, Lingen Huang, Uwe Hübner, Oliver Humphries, Brian Edward Marré, Josefine Metzkes-Ng, Thomas Miethlinger, Motoaki Nakatsutsumi, Özgül Öztürk, Xiayun Pan, Franziska Paschke-Brühl, Alexander Pelka, Irene Prencipe, Thomas R. Preston, Lisa Randolph, Hans-Peter Schlenvoigt, Jan-Patrick Schwinkendorf, Michal Šmíd, Sebastian Starke, Radka Štefaníková, Erik Thiessenhusen, Toma Toncian, Karl Zeil, Ulrich Schramm, Thomas E. Cowan, Thomas Kluge","doi":"10.1038/s42005-024-01776-6","DOIUrl":"10.1038/s42005-024-01776-6","url":null,"abstract":"Ultra-intense lasers that ionize atoms and accelerate electrons in solids to near the speed of light can lead to kinetic instabilities that alter the laser absorption and subsequent electron transport, isochoric heating, and ion acceleration. These instabilities can be difficult to characterize, but X-ray scattering at keV photon energies allows for their visualization with femtosecond temporal resolution on the few nanometer mesoscale. Here, we perform such experiment on laser-driven flat silicon membranes that shows the development of structure with a dominant scale of 60 nm in the plane of the laser axis and laser polarization, and 95 nm in the vertical direction with a growth rate faster than 0.1 fs−1. Combining the XFEL experiments with simulations provides a complete picture of the structural evolution of ultra-fast laser-induced plasma density development, indicating the excitation of plasmons and a filamentation instability. Particle-in-cell simulations confirm that these signals are due to an oblique two-stream filamentation instability. These findings provide new insight into ultra-fast instability and heating processes in solids under extreme conditions at the nanometer level with possible implications for laser particle acceleration, inertial confinement fusion, and laboratory astrophysics. Ultrafast relativistic plasma instabilities accompany and influence laser matter interactions that accelerate particlebeams with potential applications in e.g radiotherapy or fussion fast ignition scenarios. Here, the authors use Small Angle X-ray Scattering to observe such instabilities on a femtosecond, tens of nanometer scale in solids, and draw conclusions on the underlying plasma dynamics.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01776-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142130460","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-03DOI: 10.1038/s42005-024-01784-6
Young Dae Yoon, Modhuchandra Laishram, Thomas Earle Moore, Gunsu S. Yun
Magnetic flux ropes are pivotal structures and building blocks in astrophysical and laboratory plasmas, and various equilibrium models have thus been studied in the past. However, flux ropes in general form at non-equilibrium, and their pathway from formation to relaxation is a crucial process that determines their eventual properties. Here we show that any localized current parallel to a background magnetic field will evolve into a flux rope via non-equilibrium processes. The detailed kinetic dynamics are exhaustively explained through single-particle and Vlasov analyses and verified through particle-in-cell simulations. This process is consistent with many proposed mechanisms of flux rope generation such as magnetic reconnection. A spacecraft observation of an example flux rope is also presented; by invoking the non-equilibrium process, its structure and properties can be explicated down to all six components of the temperature tensor. Flux ropes are fundamental structures that govern much of the dynamics in astrophysical and space plasmas. The authors show how out-of-equilibrium processes can form small-scale flux ropes and compare them to simulations and spacecraft observations.
{"title":"Non-equilibrium formation and relaxation of magnetic flux ropes at kinetic scales","authors":"Young Dae Yoon, Modhuchandra Laishram, Thomas Earle Moore, Gunsu S. Yun","doi":"10.1038/s42005-024-01784-6","DOIUrl":"10.1038/s42005-024-01784-6","url":null,"abstract":"Magnetic flux ropes are pivotal structures and building blocks in astrophysical and laboratory plasmas, and various equilibrium models have thus been studied in the past. However, flux ropes in general form at non-equilibrium, and their pathway from formation to relaxation is a crucial process that determines their eventual properties. Here we show that any localized current parallel to a background magnetic field will evolve into a flux rope via non-equilibrium processes. The detailed kinetic dynamics are exhaustively explained through single-particle and Vlasov analyses and verified through particle-in-cell simulations. This process is consistent with many proposed mechanisms of flux rope generation such as magnetic reconnection. A spacecraft observation of an example flux rope is also presented; by invoking the non-equilibrium process, its structure and properties can be explicated down to all six components of the temperature tensor. Flux ropes are fundamental structures that govern much of the dynamics in astrophysical and space plasmas. The authors show how out-of-equilibrium processes can form small-scale flux ropes and compare them to simulations and spacecraft observations.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01784-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142130473","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-02DOI: 10.1038/s42005-024-01781-9
Aitor De Andres, Shikha Bhadoria, Javier Tello Marmolejo, Alexander Muschet, Peter Fischer, Hamid Reza Barzegar, Thomas Blackburn, Arkady Gonoskov, Dag Hanstorp, Mattias Marklund, Laszlo Veisz
Acceleration of electrons in vacuum directly by intense laser fields holds great promise for the generation of high-charge, ultrashort, relativistic electron bunches. While the energy gain is expected to be higher with tighter focusing, this does not account for the reduced acceleration range, which is limited by diffraction. Here, we present the results of an experimental investigation that exposed nanotips to relativistic few-cycle laser pulses. We demonstrate the vacuum laser acceleration of electron beams with 100s pC charge and 15 MeV energy. Two different focusing geometries, with normalized vector potential a0 of 9.8 and 3.8, produced comparable overall charge and electron spectra, despite a factor of almost ten difference in peak intensity. Our results are in good agreement with 3D particle-in-cell simulations, which indicate the importance of dephasing. Accelerating electrons in vacuum by intense laser fields is a promising yet experimentally challenging field. Here, the authors demonstrate acceleration of 100’s of pC of 15 MeV electrons by shining few-cycle laser pulses on nanotips and further investigate the process by using different focusing geometries that leads to unexpected results.
{"title":"Unforeseen advantage of looser focusing in vacuum laser acceleration","authors":"Aitor De Andres, Shikha Bhadoria, Javier Tello Marmolejo, Alexander Muschet, Peter Fischer, Hamid Reza Barzegar, Thomas Blackburn, Arkady Gonoskov, Dag Hanstorp, Mattias Marklund, Laszlo Veisz","doi":"10.1038/s42005-024-01781-9","DOIUrl":"10.1038/s42005-024-01781-9","url":null,"abstract":"Acceleration of electrons in vacuum directly by intense laser fields holds great promise for the generation of high-charge, ultrashort, relativistic electron bunches. While the energy gain is expected to be higher with tighter focusing, this does not account for the reduced acceleration range, which is limited by diffraction. Here, we present the results of an experimental investigation that exposed nanotips to relativistic few-cycle laser pulses. We demonstrate the vacuum laser acceleration of electron beams with 100s pC charge and 15 MeV energy. Two different focusing geometries, with normalized vector potential a0 of 9.8 and 3.8, produced comparable overall charge and electron spectra, despite a factor of almost ten difference in peak intensity. Our results are in good agreement with 3D particle-in-cell simulations, which indicate the importance of dephasing. Accelerating electrons in vacuum by intense laser fields is a promising yet experimentally challenging field. Here, the authors demonstrate acceleration of 100’s of pC of 15 MeV electrons by shining few-cycle laser pulses on nanotips and further investigate the process by using different focusing geometries that leads to unexpected results.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01781-9.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142130457","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-02DOI: 10.1038/s42005-024-01788-2
Grigorii P. Mikitik
Specific properties, such as surface Fermi arcs, features of quantum oscillations and of various responses to a magnetic field, distinguish Dirac semimetals from ordinary materials. These properties are determined by Dirac points at which a contact of two electron-energy bands occurs and in the vicinity of which these bands disperse linearly in the quasimomentum. This work shows that almost the same properties are inherent in a wider class of materials in which the Dirac spectrum can have a noticeable gap comparable with the Fermi energy. In other words, the degeneracy of the bands at the point and their linear dispersion are not necessary for the existence of these properties. The only sufficient condition is the following: In the vicinity of such a quasi-Dirac point, the two close bands are well described by a two-band model that takes into account the strong spin-orbit interaction. To illustrate the results, the spectrum of ZrTe5 is considered. This spectrum contains a special quasi-Dirac point, similar to that in bismuth. Dirac semimetals are 3D materials where the conduction and valence bands meet at what are called Dirac points. The author shows that almost all the properties inherent in the Dirac semimetals are exhibited by a wider class of materials that need not have the gapless Dirac points.
{"title":"Quasi-Dirac points in electron-energy spectra of crystals","authors":"Grigorii P. Mikitik","doi":"10.1038/s42005-024-01788-2","DOIUrl":"10.1038/s42005-024-01788-2","url":null,"abstract":"Specific properties, such as surface Fermi arcs, features of quantum oscillations and of various responses to a magnetic field, distinguish Dirac semimetals from ordinary materials. These properties are determined by Dirac points at which a contact of two electron-energy bands occurs and in the vicinity of which these bands disperse linearly in the quasimomentum. This work shows that almost the same properties are inherent in a wider class of materials in which the Dirac spectrum can have a noticeable gap comparable with the Fermi energy. In other words, the degeneracy of the bands at the point and their linear dispersion are not necessary for the existence of these properties. The only sufficient condition is the following: In the vicinity of such a quasi-Dirac point, the two close bands are well described by a two-band model that takes into account the strong spin-orbit interaction. To illustrate the results, the spectrum of ZrTe5 is considered. This spectrum contains a special quasi-Dirac point, similar to that in bismuth. Dirac semimetals are 3D materials where the conduction and valence bands meet at what are called Dirac points. The author shows that almost all the properties inherent in the Dirac semimetals are exhibited by a wider class of materials that need not have the gapless Dirac points.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01788-2.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142130464","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-02DOI: 10.1038/s42005-024-01791-7
Jing-Dong Bao, Xiang-Rong Wang
Physical aging appears in many systems ranging from glassy/granular materials, blinking quantum dots to laser-cooled atoms. Aging is a process with three fingerprints: (i) slow, non-exponential relaxation, (ii) breaking of time-translation-invariance, and (iii) dynamical scaling. Here, we show that all these features are present in our minimal Langevin model for aging. A natural extension of the Einstein relation, which was expected to be true in an equilibrium state, is conjectured to hold in aging processes where both the damping and the temperature decrease with time in power-law forms. The generalized Einstein relation can be used to tackle the difficult problem of determining non-ergodic behaviours. The model shows a power-law-type diffusion away from the critical point and a logarithmic Sinai-type ultra-slow diffusion at the critical point. Application to granular gases is also discussed. The authors propose a minimal Langevin model with time-dependent noise, diffusion coefficient, and friction coefficient, which is appropriate to describe cooling environments (granular gases, laser cooling). Assuming that the temperature and the friction coefficient decay in a power-law manner, the generalized Einstein relation is analysed.
{"title":"Generalized Einstein relation for aging processes","authors":"Jing-Dong Bao, Xiang-Rong Wang","doi":"10.1038/s42005-024-01791-7","DOIUrl":"10.1038/s42005-024-01791-7","url":null,"abstract":"Physical aging appears in many systems ranging from glassy/granular materials, blinking quantum dots to laser-cooled atoms. Aging is a process with three fingerprints: (i) slow, non-exponential relaxation, (ii) breaking of time-translation-invariance, and (iii) dynamical scaling. Here, we show that all these features are present in our minimal Langevin model for aging. A natural extension of the Einstein relation, which was expected to be true in an equilibrium state, is conjectured to hold in aging processes where both the damping and the temperature decrease with time in power-law forms. The generalized Einstein relation can be used to tackle the difficult problem of determining non-ergodic behaviours. The model shows a power-law-type diffusion away from the critical point and a logarithmic Sinai-type ultra-slow diffusion at the critical point. Application to granular gases is also discussed. The authors propose a minimal Langevin model with time-dependent noise, diffusion coefficient, and friction coefficient, which is appropriate to describe cooling environments (granular gases, laser cooling). Assuming that the temperature and the friction coefficient decay in a power-law manner, the generalized Einstein relation is analysed.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01791-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142130452","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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