Pub Date : 2024-08-21DOI: 10.1038/s42005-024-01758-8
Xiaodong Yang, Xinyue Long, Ran Liu, Kai Tang, Yue Zhai, Xinfang Nie, Tao Xin, Jun Li, Dawei Lu
Quantum metrology promises unprecedented precision of parameter estimation, but it is often vulnerable to noise. While significant efforts have been devoted to improving the metrology performance in Markovian environments, practical control schemes specifically designed for non-Markovian noises are much less investigated. Here, we propose two control-enhanced quantum metrology schemes that are suitable for tackling general non-Markovian noises described by noise channels or noise spectra. We conduct experiments to verify the efficacy of these schemes on a nuclear magnetic resonance system. The experimental results involving multiqubit probes show that the parameter estimation precision can be greatly improved, significantly surpassing the standard quantum limit, with our schemes. At present, non-Markovian noises are widely encountered on diverse quantum devices, the proposed schemes are relevant for realistic metrology applications on these platforms. Quantum metrology, a powerful paradigm for surpassing classical measurement precision, has been extensively studied for Markovian noise, while most practical physical processes obey non-Markovian dynamics. In this paper, the authors propose control-enhanced quantum metrology schemes to counteract non-Markovian noise and experimentally verify their efficacy.
{"title":"Control-enhanced non-Markovian quantum metrology","authors":"Xiaodong Yang, Xinyue Long, Ran Liu, Kai Tang, Yue Zhai, Xinfang Nie, Tao Xin, Jun Li, Dawei Lu","doi":"10.1038/s42005-024-01758-8","DOIUrl":"10.1038/s42005-024-01758-8","url":null,"abstract":"Quantum metrology promises unprecedented precision of parameter estimation, but it is often vulnerable to noise. While significant efforts have been devoted to improving the metrology performance in Markovian environments, practical control schemes specifically designed for non-Markovian noises are much less investigated. Here, we propose two control-enhanced quantum metrology schemes that are suitable for tackling general non-Markovian noises described by noise channels or noise spectra. We conduct experiments to verify the efficacy of these schemes on a nuclear magnetic resonance system. The experimental results involving multiqubit probes show that the parameter estimation precision can be greatly improved, significantly surpassing the standard quantum limit, with our schemes. At present, non-Markovian noises are widely encountered on diverse quantum devices, the proposed schemes are relevant for realistic metrology applications on these platforms. Quantum metrology, a powerful paradigm for surpassing classical measurement precision, has been extensively studied for Markovian noise, while most practical physical processes obey non-Markovian dynamics. In this paper, the authors propose control-enhanced quantum metrology schemes to counteract non-Markovian noise and experimentally verify their efficacy.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-08-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01758-8.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142013665","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 : 2024-08-20DOI: 10.1038/s42005-024-01768-6
Michal Stransky, Thomas J. Lane, Alexander Gorel, Sébastien Boutet, Ilme Schlichting, Adrian P. Mancuso, Zoltan Jurek, Beata Ziaja
In the warm dense matter (WDM) regime, where condensed, gas, and plasma phases coexist, matter frequently exhibits unusual properties that cannot be described by contemporary theory. Experiments reporting phenomena in WDM are therefore of interest to advance our physical understanding of this regime, which is found in dwarf stars, giant planets, and fusion ignition experiments. Using 7.1 keV X-ray free electron laser radiation (nominally 5×105 J/cm2), we produced and probed transient WDM in liquid water. Wide-angle X-ray scattering (WAXS) from the probe reveals a new ~9 Å structure that forms within 75 fs. By 100 fs, the WAXS peak corresponding to this new structure is of comparable magnitude to the ambient water peak, which is attenuated. Simulations suggest that the experiment probes a superposition of two regimes. In the first, fluences expected at the focus severely ionize the water, which becomes effectively transparent to the probe. In the second, out-of-focus pump radiation produces O1+ and O2+ ions, which rearrange due to Coulombic repulsion over 10 s of fs. Our simulations account for a decrease in ambient water signal and an increase in low-angle X-ray scattering but not the experimentally observed 9 Å feature, presenting a new challenge for theory. The ionization via high-intensity X-ray irradiation can cause structural rearrangements within the sample. The authors observe a new structure in ionized liquid water emerging within few femtoseconds from the initial ionization, characterized via a peculiar partial order on a length scale much longer than normally found in water.
在凝聚态、气态和等离子态共存的温致密物质（WDM）体系中，物质经常表现出当代理论无法描述的异常特性。因此，报告 WDM 现象的实验对于推进我们对这一机制的物理理解很有意义，矮星、巨行星和核聚变点火实验中都发现了这一机制。利用 7.1 keV X 射线自由电子激光辐射（名义上 5×105 J/cm2），我们在液态水中产生并探测了瞬态 WDM。探针产生的广角 X 射线散射（WAXS）揭示了在 75 fs 内形成的 ~9 Å 新结构。到 100 fs 时，与这种新结构相对应的 WAXS 峰值与环境水峰值的大小相当，而环境水峰值则有所衰减。模拟结果表明，该实验探测了两种状态的叠加。在第一种情况下，焦点处的通量会使水严重电离，从而使水对探针变得透明。在第二种情况下，焦点外的泵辐射产生 O1+ 和 O2+ 离子，由于库仑斥力，这些离子在 10 秒 fs 的时间内重新排列。我们的模拟解释了环境水信号的减少和低角 X 射线散射的增加，但没有解释实验观察到的 9 Å 特征，这对理论提出了新的挑战。通过高强度 X 射线辐照产生的电离可导致样品内部结构重排。作者观察到电离液态水在初始电离后的几飞秒内出现了一种新结构，其特征是在比通常水长得多的长度尺度上出现了一种奇特的偏序。
{"title":"Ionization by XFEL radiation produces distinct structure in liquid water","authors":"Michal Stransky, Thomas J. Lane, Alexander Gorel, Sébastien Boutet, Ilme Schlichting, Adrian P. Mancuso, Zoltan Jurek, Beata Ziaja","doi":"10.1038/s42005-024-01768-6","DOIUrl":"10.1038/s42005-024-01768-6","url":null,"abstract":"In the warm dense matter (WDM) regime, where condensed, gas, and plasma phases coexist, matter frequently exhibits unusual properties that cannot be described by contemporary theory. Experiments reporting phenomena in WDM are therefore of interest to advance our physical understanding of this regime, which is found in dwarf stars, giant planets, and fusion ignition experiments. Using 7.1 keV X-ray free electron laser radiation (nominally 5×105 J/cm2), we produced and probed transient WDM in liquid water. Wide-angle X-ray scattering (WAXS) from the probe reveals a new ~9 Å structure that forms within 75 fs. By 100 fs, the WAXS peak corresponding to this new structure is of comparable magnitude to the ambient water peak, which is attenuated. Simulations suggest that the experiment probes a superposition of two regimes. In the first, fluences expected at the focus severely ionize the water, which becomes effectively transparent to the probe. In the second, out-of-focus pump radiation produces O1+ and O2+ ions, which rearrange due to Coulombic repulsion over 10 s of fs. Our simulations account for a decrease in ambient water signal and an increase in low-angle X-ray scattering but not the experimentally observed 9 Å feature, presenting a new challenge for theory. The ionization via high-intensity X-ray irradiation can cause structural rearrangements within the sample. The authors observe a new structure in ionized liquid water emerging within few femtoseconds from the initial ionization, characterized via a peculiar partial order on a length scale much longer than normally found in water.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01768-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142013677","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}
Li4Ti5O12 (LTO) is known for its zero-strain characteristic in electrochemical applications, making it a suitable material for fast-charging applications. Here, we systematically studied the quasi-equilibrium and non-equilibrium lithium-ion transportation kinetics in LTO thin-film electrodes, across a range of scales from the crystal lattice to the microstructured electrodes. At the crystal lattice scale, during the non-equilibrium lithiation process, lithium ions are dispersedly embedded into the 16c position, resulting in more 8a → 16c migration compared with the quasi-equilibrium lithiation, and forming numerous fast lithium diffusion channels inside the LTO lattice. At the microstructural electrode scale, optical spectrum characterizations supported the “nano-filaments” lithiation model in polycrystalline LTO thin-film electrodes during the lithiation process. Our results reveal the patterns of lithium migration and distribution within the LTO thin film electrode under the non-equilibrium and quasi-equilibrium lithiation process, offering profound insights into the potential optimization strategies for enhancing the performance of fast-charging thin film batteries. Li4Ti5O12 (LTO) is an ideal battery material for fastcharging applications. The authors examine Li+ transport in LTO thin film electrodes, revealing that nonequilibrium processes result in unique Li+ occupation states that enhance Li+ diffusion. Findings suggests engineering Li+ occupations in LTO crystal lattice can improve battery performance.
{"title":"Nonequilibrium fast-lithiation of Li4Ti5O12 thin film anode for LIBs","authors":"Yue Chen, Shaohua Zhang, Jiefeng Ye, Xinyi Zheng, Jian-Min Zhang, Nagarathinam Mangayarkarasi, Yubiao Niu, Hongyi Lu, Guiying Zhao, Jianming Tao, Jiaxin Li, Yingbin Lin, Oleg V. Kolosov, Zhigao Huang","doi":"10.1038/s42005-024-01775-7","DOIUrl":"10.1038/s42005-024-01775-7","url":null,"abstract":"Li4Ti5O12 (LTO) is known for its zero-strain characteristic in electrochemical applications, making it a suitable material for fast-charging applications. Here, we systematically studied the quasi-equilibrium and non-equilibrium lithium-ion transportation kinetics in LTO thin-film electrodes, across a range of scales from the crystal lattice to the microstructured electrodes. At the crystal lattice scale, during the non-equilibrium lithiation process, lithium ions are dispersedly embedded into the 16c position, resulting in more 8a → 16c migration compared with the quasi-equilibrium lithiation, and forming numerous fast lithium diffusion channels inside the LTO lattice. At the microstructural electrode scale, optical spectrum characterizations supported the “nano-filaments” lithiation model in polycrystalline LTO thin-film electrodes during the lithiation process. Our results reveal the patterns of lithium migration and distribution within the LTO thin film electrode under the non-equilibrium and quasi-equilibrium lithiation process, offering profound insights into the potential optimization strategies for enhancing the performance of fast-charging thin film batteries. Li4Ti5O12 (LTO) is an ideal battery material for fastcharging applications. The authors examine Li+ transport in LTO thin film electrodes, revealing that nonequilibrium processes result in unique Li+ occupation states that enhance Li+ diffusion. Findings suggests engineering Li+ occupations in LTO crystal lattice can improve battery performance.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01775-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142013705","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}
Dissipative Kerr soliton microcombs in microresonators have enabled fundamental advances in chip-scale precision metrology, communication, spectroscopy, and parallel signal processing. Here we demonstrate polarization-diverse soliton transitions and deterministic switching dynamics of a self-stabilized microcomb in a strongly-coupled dispersion-managed microresonator driven with a single pump laser. The switching dynamics are induced by the differential thermorefractivity between coupled transverse-magnetic and transverse-electric supermodes during the forward-backward pump detunings. The achieved large soliton existence range and deterministic transitions benefit from the switching dynamics, leading to the cross-polarized soliton microcomb formation when driven in the transverse-magnetic supermode of the single resonator. Secondly, we demonstrate two distinct polarization-diverse soliton formation routes – arising from chaotic or periodically-modulated waveforms via pump power selection. Thirdly, to observe the cross-polarized supermode transition dynamics, we develop a parametric temporal magnifier with picosecond resolution, MHz frame rate and sub-ns temporal windows. We construct picosecond temporal transition portraits in 100-ns recording length of the strongly-coupled solitons, mapping the transitions from multiple soliton molecular states to singlet solitons. This study underpins polarization-diverse soliton microcombs for chip-scale ultrashort pulse generation, supporting applications in frequency and precision metrology, communications, spectroscopy and information processing. Thermal Instability hinders reliable generation of dissipative Kerr solitons in Silicon Nitride microresonators. The authors investigate a regime where polarization-diverse soliton transitions and deterministic dynamics of a self-stabilized microcomb in a dispersion managed microresonator driven with a single pump laser.
{"title":"Polarization-diverse soliton transitions and deterministic switching dynamics in strongly-coupled and self-stabilized microresonator frequency combs","authors":"Wenting Wang, Alwaleed Aldhafeeri, Heng Zhou, Tristan Melton, Xinghe Jiang, Abhinav Kumar Vinod, Mingbin Yu, Guo-Qiang Lo, Dim-Lee Kwong, Chee Wei Wong","doi":"10.1038/s42005-024-01773-9","DOIUrl":"10.1038/s42005-024-01773-9","url":null,"abstract":"Dissipative Kerr soliton microcombs in microresonators have enabled fundamental advances in chip-scale precision metrology, communication, spectroscopy, and parallel signal processing. Here we demonstrate polarization-diverse soliton transitions and deterministic switching dynamics of a self-stabilized microcomb in a strongly-coupled dispersion-managed microresonator driven with a single pump laser. The switching dynamics are induced by the differential thermorefractivity between coupled transverse-magnetic and transverse-electric supermodes during the forward-backward pump detunings. The achieved large soliton existence range and deterministic transitions benefit from the switching dynamics, leading to the cross-polarized soliton microcomb formation when driven in the transverse-magnetic supermode of the single resonator. Secondly, we demonstrate two distinct polarization-diverse soliton formation routes – arising from chaotic or periodically-modulated waveforms via pump power selection. Thirdly, to observe the cross-polarized supermode transition dynamics, we develop a parametric temporal magnifier with picosecond resolution, MHz frame rate and sub-ns temporal windows. We construct picosecond temporal transition portraits in 100-ns recording length of the strongly-coupled solitons, mapping the transitions from multiple soliton molecular states to singlet solitons. This study underpins polarization-diverse soliton microcombs for chip-scale ultrashort pulse generation, supporting applications in frequency and precision metrology, communications, spectroscopy and information processing. Thermal Instability hinders reliable generation of dissipative Kerr solitons in Silicon Nitride microresonators. The authors investigate a regime where polarization-diverse soliton transitions and deterministic dynamics of a self-stabilized microcomb in a dispersion managed microresonator driven with a single pump laser.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-08-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01773-9.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142013685","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 : 2024-08-16DOI: 10.1038/s42005-024-01770-y
Qiaoli Yang, Yu Gao, Zhihui Peng
Exploring the mysterious dark matter is a key quest in modern physics. Currently, detecting axions, a hypothetical particle proposed as a primary component of dark matter, remains a significant challenge due to their weakly interacting nature. Here we show at quantum level that in a cavity permeated by a magnetic field, the single axion-photon conversion rate is enhanced by the cavity quality factor and is quantitatively larger than the classical result by π/2. The axion cavity can be considered a quantum device emitting single photons with temporal separations. This differs from the classical picture and reveals a possibility for the axion cavity experiment to handle the signal sensitivity at the quantum level, e.g., a dual path quantum interferometry with cross-power and second-order correlation measurements. This scheme would greatly reduce the signal scanning time and improve the sensitivity of the axion-photon coupling, potentially leading to the direct observation of axions. Axions are the top contenders for explaining the enigmatic dark matter in the Universe. The authors present the inaugural quantum-level validation of a cavity’s resonant boost to the conversion of axions into photons, thus employing a dual-path interferometry method can greatly enhance the signal-to-noise ratio in the experiments, enabling swifter scans and a better detection sensitivity for the evasive axion dark matter.
{"title":"Quantum dual-path interferometry scheme for axion dark matter searches","authors":"Qiaoli Yang, Yu Gao, Zhihui Peng","doi":"10.1038/s42005-024-01770-y","DOIUrl":"10.1038/s42005-024-01770-y","url":null,"abstract":"Exploring the mysterious dark matter is a key quest in modern physics. Currently, detecting axions, a hypothetical particle proposed as a primary component of dark matter, remains a significant challenge due to their weakly interacting nature. Here we show at quantum level that in a cavity permeated by a magnetic field, the single axion-photon conversion rate is enhanced by the cavity quality factor and is quantitatively larger than the classical result by π/2. The axion cavity can be considered a quantum device emitting single photons with temporal separations. This differs from the classical picture and reveals a possibility for the axion cavity experiment to handle the signal sensitivity at the quantum level, e.g., a dual path quantum interferometry with cross-power and second-order correlation measurements. This scheme would greatly reduce the signal scanning time and improve the sensitivity of the axion-photon coupling, potentially leading to the direct observation of axions. Axions are the top contenders for explaining the enigmatic dark matter in the Universe. The authors present the inaugural quantum-level validation of a cavity’s resonant boost to the conversion of axions into photons, thus employing a dual-path interferometry method can greatly enhance the signal-to-noise ratio in the experiments, enabling swifter scans and a better detection sensitivity for the evasive axion dark matter.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01770-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141991741","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}
Exploiting the utility of near-term quantum devices is a long-standing challenge whereas hybrid quantum machine learning emerges as a promising candidate. Here we propose a quantum-enhanced deep generative algorithm based on programmable quantum circuit-induced quantum latent codes. To validate the effectiveness of the algorithm, we conduct optical ghost imaging experiments, collecting dataset under varying physical sampling rates. Leveraging a physically enhanced loss function and a pretrained neural network, the quantum algorithm exhibits superior reconstruction performance compared to conventional algorithms. We observe the learnable quantum latent space enhances the out-of-distribution generalization capability of the pretrained model. In the context of computer vision problems, numerical results indicate that quantum latent space can increase the generation diversity of the pretrained model. Furthermore, the algorithm outperforms classical counterparts, particularly in image inpainting and colorization, by a significant margin. Our study demonstrates the utility of hybrid quantum-classical algorithms in enhancing generalization capability, highlighting the potential of near-term quantum devices in large-scale generative artificial intelligence. Quantum circuits can generate hard distributions. Exploiting this known fact, the authors train a mixture of parametric quantum circuits and classical neural networks and show that the addition of the quantum part can enhance the expressive power of the model for generative AI.
{"title":"Quantum deep generative prior with programmable quantum circuits","authors":"Tailong Xiao, Xinliang Zhai, Jingzheng Huang, Jianping Fan, Guihua Zeng","doi":"10.1038/s42005-024-01765-9","DOIUrl":"10.1038/s42005-024-01765-9","url":null,"abstract":"Exploiting the utility of near-term quantum devices is a long-standing challenge whereas hybrid quantum machine learning emerges as a promising candidate. Here we propose a quantum-enhanced deep generative algorithm based on programmable quantum circuit-induced quantum latent codes. To validate the effectiveness of the algorithm, we conduct optical ghost imaging experiments, collecting dataset under varying physical sampling rates. Leveraging a physically enhanced loss function and a pretrained neural network, the quantum algorithm exhibits superior reconstruction performance compared to conventional algorithms. We observe the learnable quantum latent space enhances the out-of-distribution generalization capability of the pretrained model. In the context of computer vision problems, numerical results indicate that quantum latent space can increase the generation diversity of the pretrained model. Furthermore, the algorithm outperforms classical counterparts, particularly in image inpainting and colorization, by a significant margin. Our study demonstrates the utility of hybrid quantum-classical algorithms in enhancing generalization capability, highlighting the potential of near-term quantum devices in large-scale generative artificial intelligence. Quantum circuits can generate hard distributions. Exploiting this known fact, the authors train a mixture of parametric quantum circuits and classical neural networks and show that the addition of the quantum part can enhance the expressive power of the model for generative AI.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01765-9.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141986157","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 : 2024-08-14DOI: 10.1038/s42005-024-01767-7
Jin-Yu Zou, Bo Fu, Shun-Qing Shen
Two-dimensional topological semimetals are typically characterized by the vorticity of gapless points, and can be classified according to the band representations. However, the topological properties involving the distribution of the Berry curvature in the entire Brillouin zone are often overlooked. In this study, we investigate a two-band two-dimensional topological semimetal protected by C4zT magnetic symmetry, exhibiting a two-fold band degeneracy at the Γ(0, 0) and M(π, π) points. Due to the presence of C4zT symmetry, the Brillouin zone is divided into two patches characterized by half-quantized Berry curvature fluxes with opposite signs. In multi-band case, the half-quantization deviates, indicating the fragile nature. The semimetal presents counter-propagating half-edge channels, accompanied by power-law decaying and oscillating edge currents. The band topology leads to unconventional Landau levels featuring anisotropic edge modes. Each massless Dirac cone, associated with the half-quantized Berry curvature flux, exhibits an integer quantum Hall conductance. Additionally, we calculate the local orbital magnetization with open boundary conditions in both the x and y directions. This reveals isolated magnetization islands, highlighting an experimentally observable magnetic phenomenon in this topological semimetal. A two-dimensional semimetal is featured by its low energy physics near the degeneracy points, while the topology over the whole Brillouin zone is rarely studied. The authors find that the Brillouin zone of the C4zT symmetric semimetal is partitioned into two patches characterized by half quantized Berry curvature fluxes with opposite signs, accompanied by the topological transport phenomena.
二维拓扑半金属通常以无间隙点的涡度为特征，并可根据带状表示进行分类。然而，涉及贝里曲率在整个布里渊区分布的拓扑特性却常常被忽视。在本研究中，我们研究了一种受 C4zT 磁对称性保护的双带二维拓扑半金属，它在Γ(0, 0) 点和 M(π, π) 点表现出双倍带退性。由于 C4zT 对称性的存在，布里渊区被划分为两块，其特征是具有相反符号的半量化贝里曲率通量。在多波段情况下，半量化出现偏差，表明其性质脆弱。半金属呈现出反向传播的半边通道，并伴有幂律衰减和振荡边缘电流。带拓扑结构导致了以各向异性边缘模式为特征的非常规朗道水平。与半量化贝里曲率通量相关的每个无质量狄拉克锥都表现出整数量子霍尔电导。此外，我们还利用 x 和 y 方向的开放边界条件计算了局部轨道磁化。这揭示了孤立的磁化岛，凸显了这种拓扑半金属中可通过实验观察到的磁现象。二维半金属的特点是其在退化点附近的低能物理学，而整个布里渊区的拓扑结构却很少被研究。作者发现，C4zT 对称半金属的布里渊区被分割成两块，其特征是具有相反符号的半量化贝里曲率通量，并伴有拓扑输运现象。
{"title":"Topological properties of C4zT-symmetric semimetals","authors":"Jin-Yu Zou, Bo Fu, Shun-Qing Shen","doi":"10.1038/s42005-024-01767-7","DOIUrl":"10.1038/s42005-024-01767-7","url":null,"abstract":"Two-dimensional topological semimetals are typically characterized by the vorticity of gapless points, and can be classified according to the band representations. However, the topological properties involving the distribution of the Berry curvature in the entire Brillouin zone are often overlooked. In this study, we investigate a two-band two-dimensional topological semimetal protected by C4zT magnetic symmetry, exhibiting a two-fold band degeneracy at the Γ(0, 0) and M(π, π) points. Due to the presence of C4zT symmetry, the Brillouin zone is divided into two patches characterized by half-quantized Berry curvature fluxes with opposite signs. In multi-band case, the half-quantization deviates, indicating the fragile nature. The semimetal presents counter-propagating half-edge channels, accompanied by power-law decaying and oscillating edge currents. The band topology leads to unconventional Landau levels featuring anisotropic edge modes. Each massless Dirac cone, associated with the half-quantized Berry curvature flux, exhibits an integer quantum Hall conductance. Additionally, we calculate the local orbital magnetization with open boundary conditions in both the x and y directions. This reveals isolated magnetization islands, highlighting an experimentally observable magnetic phenomenon in this topological semimetal. A two-dimensional semimetal is featured by its low energy physics near the degeneracy points, while the topology over the whole Brillouin zone is rarely studied. The authors find that the Brillouin zone of the C4zT symmetric semimetal is partitioned into two patches characterized by half quantized Berry curvature fluxes with opposite signs, accompanied by the topological transport phenomena.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01767-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141986153","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 : 2024-08-14DOI: 10.1038/s42005-024-01708-4
Hong Chul Choi, Seung Hun Lee, Bohm-Jung Yang
UTe2 is a promising candidate for spin-triplet superconductors, in which a paramagnetic normal state becomes superconducting due to spin fluctuations. Here, we theoretically show that electron correlation induces a dramatic change in the normal state fermiology with an emergent correlated Fermi surface (FS) driven by Kondo resonance at low temperatures. This emergent correlated FS can account for various unconventional superconducting properties in a unified way. In particular, the geometry of the correlated FS can naturally host topological superconductivity in the presence of odd-parity pairings, which become the leading instability due to strong ferromagnetic spin fluctuations. Moreover, two pairs of odd-parity channels appear as nearly degenerate solutions which may lead to time-reversal breaking multicomponent superconductivity. The resulting time-reversal-breaking superconducting state is a Weyl superconductor in which Weyl points migrate along the correlated FS as the relative magnitude of nearly degenerate pairing solutions varies. UTe2 is a promising candidate for spin-triplet unconventional topological superconductivity. The authors theoretically show that electron correlation induces a dramatic change in the normal state fermiology of this material with an emergent correlated Fermi surface driven by Kondo resonance at low temperatures, which can account for various unconventional superconducting properties in a unified way.
{"title":"Correlated normal state fermiology and topological superconductivity in UTe2","authors":"Hong Chul Choi, Seung Hun Lee, Bohm-Jung Yang","doi":"10.1038/s42005-024-01708-4","DOIUrl":"10.1038/s42005-024-01708-4","url":null,"abstract":"UTe2 is a promising candidate for spin-triplet superconductors, in which a paramagnetic normal state becomes superconducting due to spin fluctuations. Here, we theoretically show that electron correlation induces a dramatic change in the normal state fermiology with an emergent correlated Fermi surface (FS) driven by Kondo resonance at low temperatures. This emergent correlated FS can account for various unconventional superconducting properties in a unified way. In particular, the geometry of the correlated FS can naturally host topological superconductivity in the presence of odd-parity pairings, which become the leading instability due to strong ferromagnetic spin fluctuations. Moreover, two pairs of odd-parity channels appear as nearly degenerate solutions which may lead to time-reversal breaking multicomponent superconductivity. The resulting time-reversal-breaking superconducting state is a Weyl superconductor in which Weyl points migrate along the correlated FS as the relative magnitude of nearly degenerate pairing solutions varies. UTe2 is a promising candidate for spin-triplet unconventional topological superconductivity. The authors theoretically show that electron correlation induces a dramatic change in the normal state fermiology of this material with an emergent correlated Fermi surface driven by Kondo resonance at low temperatures, which can account for various unconventional superconducting properties in a unified way.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01708-4.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141980520","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 : 2024-08-14DOI: 10.1038/s42005-024-01763-x
Luuk Coopmans, Marcello Benedetti
Quantum Boltzmann machines (QBMs) are machine-learning models for both classical and quantum data. We give an operational definition of QBM learning in terms of the difference in expectation values between the model and target, taking into account the polynomial size of the data set. By using the relative entropy as a loss function, this problem can be solved without encountering barren plateaus. We prove that a solution can be obtained with stochastic gradient descent using at most a polynomial number of Gibbs states. We also prove that pre-training on a subset of the QBM parameters can only lower the sample complexity bounds. In particular, we give pre-training strategies based on mean-field, Gaussian Fermionic, and geometrically local Hamiltonians. We verify these models and our theoretical findings numerically on a quantum and a classical data set. Our results establish that QBMs are promising machine learning models. The quantum Boltzmann machine (QBM) is a machine learning model with applications ranging from generative modeling to the initialization of neural networks and physics models of experimental data. Here the authors show that QBMs can be trained sample efficiently and that the sample complexity can be further reduced with pre-training strategies.
{"title":"On the sample complexity of quantum Boltzmann machine learning","authors":"Luuk Coopmans, Marcello Benedetti","doi":"10.1038/s42005-024-01763-x","DOIUrl":"10.1038/s42005-024-01763-x","url":null,"abstract":"Quantum Boltzmann machines (QBMs) are machine-learning models for both classical and quantum data. We give an operational definition of QBM learning in terms of the difference in expectation values between the model and target, taking into account the polynomial size of the data set. By using the relative entropy as a loss function, this problem can be solved without encountering barren plateaus. We prove that a solution can be obtained with stochastic gradient descent using at most a polynomial number of Gibbs states. We also prove that pre-training on a subset of the QBM parameters can only lower the sample complexity bounds. In particular, we give pre-training strategies based on mean-field, Gaussian Fermionic, and geometrically local Hamiltonians. We verify these models and our theoretical findings numerically on a quantum and a classical data set. Our results establish that QBMs are promising machine learning models. The quantum Boltzmann machine (QBM) is a machine learning model with applications ranging from generative modeling to the initialization of neural networks and physics models of experimental data. Here the authors show that QBMs can be trained sample efficiently and that the sample complexity can be further reduced with pre-training strategies.","PeriodicalId":10540,"journal":{"name":"Communications Physics","volume":null,"pages":null},"PeriodicalIF":5.4,"publicationDate":"2024-08-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s42005-024-01763-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141980507","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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