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Quantum algorithm for neighborhood preserving embedding Shi-Jie Pan(潘世杰), Lin-Chun Wan(万林春), Hai-Ling Liu(刘海玲), Yu-Sen Wu(吴宇森), Su-Juan Qin(秦素娟), Qiao-Yan Wen(温巧燕), and Fei Gao(高飞) Chin. Phys. B, 2022, 31 (6): 060304.   DOI: 10.1088/1674-1056/ac523a Abstract （135）   HTML （2）    PDF （911KB）（122）       Knowledge map    Neighborhood preserving embedding (NPE) is an important linear dimensionality reduction technique that aims at preserving the local manifold structure. NPE contains three steps, i.e., finding the nearest neighbors of each data point, constructing the weight matrix, and obtaining the transformation matrix. Liang et al. proposed a variational quantum algorithm (VQA) for NPE [Phys. Rev. A 101 032323 (2020)]. The algorithm consists of three quantum sub-algorithms, corresponding to the three steps of NPE, and was expected to have an exponential speedup on the dimensionality n. However, the algorithm has two disadvantages: (i) It is not known how to efficiently obtain the input of the third sub-algorithm from the output of the second one. (ii) Its complexity cannot be rigorously analyzed because the third sub-algorithm in it is a VQA. In this paper, we propose a complete quantum algorithm for NPE, in which we redesign the three sub-algorithms and give a rigorous complexity analysis. It is shown that our algorithm can achieve a polynomial speedup on the number of data points m and an exponential speedup on the dimensionality n under certain conditions over the classical NPE algorithm, and achieve a significant speedup compared to Liang et al.'s algorithm even without considering the complexity of the VQA.

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Fast prediction of aerodynamic noise induced by the flow around a cylinder based on deep neural network Hai-Yang Meng(孟海洋), Zi-Xiang Xu(徐自翔), Jing Yang(杨京), Bin Liang(梁彬), and Jian-Chun Cheng(程建春) Chin. Phys. B, 2022, 31 (6): 064305.   DOI: 10.1088/1674-1056/ac5e98 Abstract （60）   HTML （0）    PDF （1086KB）（56）       Knowledge map    Accurate and fast prediction of aerodynamic noise has always been a research hotspot in fluid mechanics and aeroacoustics. The conventional prediction methods based on numerical simulation often demand huge computational resources, which are difficult to balance between accuracy and efficiency. Here, we present a data-driven deep neural network (DNN) method to realize fast aerodynamic noise prediction while maintaining accuracy. The proposed deep learning method can predict the spatial distributions of aerodynamic noise information under different working conditions. Based on the large eddy simulation turbulence model and the Ffowcs Williams-Hawkings acoustic analogy theory, a dataset composed of 1216 samples is established. With reference to the deep learning method, a DNN framework is proposed to map the relationship between spatial coordinates, inlet velocity and overall sound pressure level. The root-mean-square-errors of prediction are below 0.82 dB in the test dataset, and the directivity of aerodynamic noise predicted by the DNN framework are basically consistent with the numerical simulation. This work paves a novel way for fast prediction of aerodynamic noise with high accuracy and has application potential in acoustic field prediction.

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Uniaxial stress effect on quasi-one-dimensional Kondo lattice CeCo2Ga8 Kangqiao Cheng(程康桥), Binjie Zhou(周斌杰), Cuixiang Wang(王翠香), Shuo Zou(邹烁), Yupeng Pan(潘宇鹏), Xiaobo He(何晓波), Jian Zhang(张健), Fangjun Lu(卢方君), Le Wang(王乐), Youguo Shi(石友国), and Yongkang Luo(罗永康) Chin. Phys. B, 2022, 31 (6): 067104.   DOI: 10.1088/1674-1056/ac6339 Abstract （48）   HTML （3）    PDF （1321KB）（29）       Knowledge map    Quantum critical phenomena in the quasi-one-dimensional limit remain an open issue. We report the uniaxial stress effect on the quasi-one-dimensional Kondo lattice CeCo$_2$Ga$_8$ by electric transport and AC heat capacity measurements. CeCo$_2$Ga$_8$ is speculated to sit in close vicinity but on the quantum-disordered side of a quantum critical point. Upon compressing the ${c}$ axis, parallel to the Ce-Ce chain, the onset of coherent Kondo effect is enhanced. In contrast, the electronic specific heat diverges more rapidly at low temperature when the intra-chain distance is elongated by compressions along ${a}$ or ${b}$ axis. These results suggest that a tensile intra-chain strain ($\varepsilon_c >0$) pushes CeCo$_2$Ga$_8$ closer to the quantum critical point, while a compressive intra-chain strain ($\varepsilon_c<0$) likely causes departure. Our work provides a rare paradigm of manipulation near a quantum critical point in a quasi-1D Kondo lattice by uniaxial stress, and paves the way for further investigations on the unique feature of quantum criticality in the quasi-1D limit.

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Spin freezing in the van der Waals material Mn2Ga2S5 Jie Shen(沈洁), Xitong Xu(许锡童), Miao He(何苗), Yonglai Liu(刘永来), Yuyan Han(韩玉岩), and Zhe Qu(屈哲) Chin. Phys. B, 2022, 31 (6): 067105.   DOI: 10.1088/1674-1056/ac657c Abstract （39）   HTML （0）    PDF （1270KB）（30）       Knowledge map    Geometrical frustration in low-dimensional magnetic systems has been an intriguing research aspect, where the suppression of conventional magnetic order may lead to exotic ground states such as spin glass or spin liquid. In this work we report the synthesis and magnetism study of the monocrystalline Mn$_2$Ga$_2$S$_5$, featuring both the van der Waals structure and a bilayered triangular Mn lattice. Magnetic susceptibility reveals a significant antiferromagnetic interaction with a Curie-Weiss temperature $\theta_{\rm w}\sim-260$ K and a high spin $S=5/2$ Mn$^{2+}$ state. However, no long range magnetic order has been found down to 2 K, and a spin freezing transition is found to occur at around 12 K well below its $\theta_{\rm w}$. This yields a frustration index of $f = -\theta_{\rm w}/T_{\rm f} \approx 22$, an indication that the system is highly frustrated. The absence of a double-peak structure in magnetic specific heat compared with the $TM_2$S$_4$ compounds implies that the spin freezing behavior in Mn$_2$Ga$_2$S$_5$ is a result of the competition between exchange interactions and the 2D crystalline structure. Our results suggest that the layered Mn$_2$Ga$_2$S$_5$ would be an excellent candidate for investigating the physics of 2D magnetism and spin disordered state.

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Experimental observation of pseudogap in a modulation-doped Mott insulator: Sn/Si(111)-(√30×√30)R30° Yan-Ling Xiong(熊艳翎), Jia-Qi Guan(关佳其), Rui-Feng Wang(汪瑞峰), Can-Li Song(宋灿立), Xu-Cun Ma(马旭村), and Qi-Kun Xue(薛其坤) Chin. Phys. B, 2022, 31 (6): 067401.   DOI: 10.1088/1674-1056/ac65f2 Abstract （61）   HTML （1）    PDF （2064KB）（47）       Knowledge map    Unusual quantum phenomena usually emerge upon doping Mott insulators. Using a molecular beam epitaxy system integrated with cryogenic scanning tunneling microscope, we investigate the electronic structure of a modulation-doped Mott insulator Sn/Si(111)-($\sqrt{3}\times \sqrt{3})R$30$^\circ$. In underdoped regions, we observe a universal pseudogap opening around the Fermi level, which changes little with the applied magnetic field and the occurrence of Sn vacancies. The pseudogap gets smeared out at elevated temperatures and alters in size with the spatial confinement of the Mott insulating phase. Our findings, along with the previously observed superconductivity at a higher doping level, are highly reminiscent of the electronic phase diagram in the doped copper oxide compounds.

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Non-volatile multi-state magnetic domain transformation in a Hall balance Yang Gao(高阳), Jingyan Zhang(张静言), Pengwei Dou(窦鹏伟), Zhuolin Li(李卓霖), Zhaozhao Zhu(朱照照), Yaqin Guo(郭雅琴), Chaoqun Hu(胡超群), Weidu Qin(覃维都), Congli He(何聪丽), Shipeng Shen(申世鹏), Ying Zhang(张颖), and Shouguo Wang(王守国) Chin. Phys. B, 2022, 31 (6): 067502.   DOI: 10.1088/1674-1056/ac65f5 Abstract （37）   HTML （0）    PDF （7265KB）（25）       Knowledge map    High performance of the generation, stabilization and manipulation of magnetic skyrmions prompts the application of topological multilayers in spintronic devices. Skyrmions in synthetic antiferromagnets (SAF) have been considered as a promising alternative to overcome the limitations of ferromagnetic skyrmions, such as the skyrmion Hall effect and stray magnetic field. Here, by using the Lorentz transmission electron microscopy, the interconversion between the single domain, labyrinth domain and skyrmion state can be observed by the combined manipulation of electric current and magnetic field in a Hall balance (a SAF with the core structure of [Co/Pt]4/NiO/[Co/Pt]4 showing perpendicular magnetic anisotropy). Furthermore, high-density room temperature skyrmions can be stabilized at zero field while the external stimulus is removed and the skyrmion density is tunable. The generation and manipulation method of skyrmions in Hall balance in this study opens up a promising way to engineer SAF-skyrmion-based memory devices.

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Force-constant-decayed anisotropic network model: An improved method for predicting RNA flexibility Wei-Bu Wang(王韦卜), Xing-Yuan Li(李兴元), and Ji-Guo Su(苏计国) Chin. Phys. B, 2022, 31 (6): 068704.   DOI: 10.1088/1674-1056/ac560e Abstract （57）   HTML （0）    PDF （1413KB）（29）       Knowledge map    RNA is an important biological macromolecule, which plays an irreplaceable role in many life activities. RNA functions are largely determined by its tertiary structure and the intrinsic dynamics encoded in the structure. Thus, how to effective extract structure-encoded dynamics is of great significance for understanding RNA functions. Anisotropic network model (ANM) is an efficient method to investigate macromolecular dynamical properties, which has been widely used in protein studies. However, the performance of the conventional ANM in describing RNA flexibility is not as good as that on proteins. In this study, we proposed a new approach, named force-constant-decayed anisotropic network model (fcd-ANM), to improve the performance in investigating the dynamical properties encoded in RNA structures. In fcd-ANM, nucleotide pairs in RNA structure were connected by springs and the force constant of springs was decayed exponentially based on the separation distance to describe the differences in the inter-nucleotide interaction strength. The performance of fcd-ANM in predicting RNA flexibility was evaluated using a non-redundant structure database composed of 51 RNAs. The results indicate that fcd-ANM significantly outperforms the conventional ANM in reproducing the experimental B-factors of nucleotides in RNA structures, and the Pearson correlation coefficient between the predicted and experimental nucleotide B-factors was distinctly improved by 21.05% compared to the conventional ANM. Fcd-ANM can serve as a more effective method for analysis of RNA dynamical properties.

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Gauss quadrature based finite temperature Lanczos method Jian Li(李健) and Hai-Qing Lin(林海青) Chin. Phys. B, 2022, 31 (5): 050203.   DOI: 10.1088/1674-1056/ac5986 Abstract （337）   HTML （4）    PDF （782KB）（336）       Knowledge map    The finite temperature Lanczos method (FTLM), which is an exact diagonalization method intensively used in quantum many-body calculations, is formulated in the framework of orthogonal polynomials and Gauss quadrature. The main idea is to reduce finite temperature static and dynamic quantities into weighted summations related to one- and two-dimensional Gauss quadratures. Then lower order Gauss quadrature, which is generated from Lanczos iteration, can be applied to approximate the initial weighted summation. This framework fills the conceptual gap between FTLM and kernel polynomial method, and makes it easy to apply orthogonal polynomial techniques in the FTLM calculation.

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Pressure-induced phase transitions in the ZrXY (X= Si, Ge, Sn;Y= S, Se, Te) family compounds Qun Chen(陈群), Juefei Wu(吴珏霏), Tong Chen(陈统), Xiaomeng Wang(王晓梦), Chi Ding(丁弛), Tianheng Huang(黄天衡), Qing Lu(鲁清), and Jian Sun(孙建) Chin. Phys. B, 2022, 31 (5): 056201.   DOI: 10.1088/1674-1056/ac5989 Abstract （176）   HTML （3）    PDF （6039KB）（225）       Knowledge map    Pressure is an effective and clean way to modify the electronic structures of materials, cause structural phase transitions and even induce the emergence of superconductivity. Here, we predicted several new phases of the ZrXY family at high pressures using the crystal structures search method together with first-principle calculations. In particular, the ZrGeS compound undergoes an isosymmetric phase transition from P4/nmm-I to P4/nmm-II at approximately 82 GPa. Electronic band structures show that all the high-pressure phases are metallic. Among these new structures, P4/nmm-II ZrGeS and P4/mmm ZrGeSe can be quenched to ambient pressure with superconducting critical temperatures of approximately 8.1 K and 8.0 K, respectively. Our study provides a way to tune the structure, electronic properties, and superconducting behavior of topological materials through pressure.

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Water contact angles on charged surfaces in aerosols Yu-Tian Shen(申钰田), Ting Lin(林挺), Zhen-Ze Yang(杨镇泽), Yong-Feng Huang(黄永峰), Ji-Yu Xu(徐纪玉), and Sheng Meng(孟胜) Chin. Phys. B, 2022, 31 (5): 056801.   DOI: 10.1088/1674-1056/ac5c2f Abstract （127）   HTML （1）    PDF （903KB）（88）       Knowledge map    Interactions between water and solid substrates are of fundamental importance to various processes in nature and industry. Electric control is widely used to modify interfacial water, where the influence of surface charges is inevitable. Here we obtain positively and negatively charged surfaces using LiTaO3 crystals and observe that a large net surface charge up to 0.1 C/m2 can nominally change the contact angles of pure water droplets comparing to the same uncharged surface. However, even a small amount of surface charge can efficiently increase the water contact angle in the presence of aerosols. Our results indicate that such surface charges can hardly affect the structure of interfacial water molecular layers and the morphology of the macroscopic droplet, while adsorption of a small amount of organic contaminants from aerosols with the help of Coulomb attraction can notably decrease the wettability of solid surface. Our results not only provide a fundamental understanding of the interactions between charged surfaces and water, but also help to develop new techniques on electric control of wettability and microfluidics in real aerosol environments.

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Generalization of the theory of three-dimensional quantum Hall effect of Fermi arcs in Weyl semimetal Mingqi Chang(苌名起), Yunfeng Ge(葛云凤), and Li Sheng(盛利) Chin. Phys. B, 2022, 31 (5): 057304.   DOI: 10.1088/1674-1056/ac5c32 Abstract （111）   HTML （2）    PDF （2213KB）（83）       Knowledge map    The quantum Hall effect (QHE), which is usually observed in two-dimensional systems, was predicted theoretically and observed experimentally in three-dimensional (3D) topological semimetal. However, there are some inconsistencies between the theory and the experiments showing the theory is imperfect. Here, we generalize the theory of the 3D QHE of Fermi arcs in Weyl semimetal. Through calculating the sheet Hall conductivity of a Weyl semimetal slab, we show that the 3D QHE of Fermi arcs can occur in a large energy range and the thickness dependences of the QHE in different Fermi energies are distinct. When the Fermi energy is near the Weyl nodes, the Fermi arcs give rise to the QHE which is independent of the thickness of the slab. When the Fermi energy is not near the Weyl nodes, the two Fermi arcs form a complete Fermi loop with the assistance of bulk states giving rise to the QHE which is dependent on the sample thickness. We also demonstrate how the band anisotropic terms influence the QHE of Fermi arcs. Our theory complements the imperfections of the present theory of 3D QHE of Fermi arcs.

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Asymmetric Fraunhofer pattern in Josephson junctions from heterodimensional superlattice V5S8 Juewen Fan(范珏雯), Bingyan Jiang(江丙炎), Jiaji Zhao(赵嘉佶), Ran Bi(毕然), Jiadong Zhou(周家东), Zheng Liu(刘政), Guang Yang(杨光), Jie Shen(沈洁), Fanming Qu(屈凡明), Li Lu(吕力), Ning Kang(康宁), and Xiaosong Wu(吴孝松) Chin. Phys. B, 2022, 31 (5): 057402.   DOI: 10.1088/1674-1056/ac5d30 Abstract （177）   HTML （2）    PDF （1074KB）（158）       Knowledge map    Introduction of spin-orbit coupling (SOC) in a Josephson junction (JJ) gives rise to unusual Josephson effects. We investigate JJs based on a newly discovered heterodimensional superlattice V5S8 with a special form of SOC. The unique homointerface of our JJs enables elimination of extrinsic effects due to interfaces and disorder. We observe asymmetric Fraunhofer patterns with respect to both the perpendicular magnetic field and the current. The asymmetry is influenced by an in-plane magnetic field. Analysis of the pattern points to a nontrivial spatial distribution of the Josephson current that is intrinsic to the SOC in V5S8.

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Dynamical signatures of the one-dimensional deconfined quantum critical point Ning Xi(西宁) and Rong Yu(俞榕) Chin. Phys. B, 2022, 31 (5): 057501.   DOI: 10.1088/1674-1056/ac5987 Abstract （109）   HTML （4）    PDF （3436KB）（83）       Knowledge map    We study the critical scaling and dynamical signatures of fractionalized excitations at two different deconfined quantum critical points (DQCPs) in an S = 1/2 spin chain using the time evolution of infinite matrix product states. The scaling of the correlation functions and the dispersion of the conserved current correlations explicitly show the emergence of enhanced continuous symmetries at these DQCPs. The dynamical structure factors in several different channels reveal the development of deconfined fractionalized excitations at the DQCPs. Furthermore, we find an effective spin-charge separation at the DQCP between the ferromagnetic (FM) and valence bond solid (VBS) phases, and identify two continua associated with different types of fractionalized excitations at the DQCP between the X-direction and Z-direction FM phases. Our findings not only provide direct evidence for the DQCP in one dimension but also shed light on exploring the DQCP in higher dimensions.

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Effects of phosphorus doping on the physical properties of axion insulator candidate EuIn2As2 Feihao Pan(潘斐豪), Congkuan Tian(田丛宽), Jiale Huang(黄嘉乐), Daye Xu(徐大业), Jinchen Wang (汪晋辰), Peng Cheng(程鹏), Juanjuan Liu(刘娟娟), and Hongxia Zhang(张红霞) Chin. Phys. B, 2022, 31 (5): 057502.   DOI: 10.1088/1674-1056/ac5d2c Abstract （59）   HTML （0）    PDF （1336KB）（71）       Knowledge map    We report an investigation on the single crystal growth, magnetic and transport properties of EuIn2(As1-xPx)2 (0≤x≤ 1). The physical properties of axion insulator candidate EuIn2As2 can be effectively tuned by P-doping. With increasing x, the c-axis lattice parameter decreases linearly, the magnetic transition temperature gradually increases and ferromagnetic interactions are enhanced. This is similar to the previously reported high pressure effect on EuIn2As2. For x=0.40, a spin glass state at Tg=10 K emerges together with the observations of a butter-fly shaped magnetic hysteresis and slow magnetic behavior. Besides, magnetic transition has great influence on the charge carriers in this system and negative colossal magnetoresistance is observed for all P-doped samples. Our findings suggest that EuIn2(As1-xPx)2 is a promising material playground for exploring novel topological states.

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Solving quantum rotor model with different Monte Carlo techniques Weilun Jiang(姜伟伦), Gaopei Pan(潘高培), Yuzhi Liu(刘毓智), and Zi-Yang Meng(孟子杨) Chin. Phys. B, 2022, 31 (4): 040504.   DOI: 10.1088/1674-1056/ac4f52 Abstract （399）   HTML （1）    PDF （1004KB）（362）       Knowledge map    We systematically test the performance of several Monte Carlo update schemes for the (2+1)d XY phase transition of quantum rotor model. By comparing the local Metropolis (LM), LM plus over-relaxation (OR), Wolff-cluster (WC), hybrid Monte Carlo (HM), hybrid Monte Carlo with Fourier acceleration (FA) schemes, it is clear that among the five different update schemes, at the quantum critical point, the WC and FA schemes acquire the smallest autocorrelation time and cost the least amount of CPU hours in achieving the same level of relative error, and FA enjoys a further advantage of easily implementable for more complicated interactions such as the long-range ones. These results bestow one with the necessary knowledge of extending the quantum rotor model, which plays the role of ferromagnetic/antiferromagnetic critical bosons or Z2 topological order, to more realistic and yet challenging models such as Fermi surface Yukawa-coupled to quantum rotor models.

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Non-invasive and low-artifact in vivo brain imaging by using a scanning acoustic-photoacoustic dual mode microscopy Wentian Chen(陈文天), Chao Tao(陶超), Zizhong Hu(胡仔仲), Songtao Yuan(袁松涛), Qinghuai Liu(刘庆淮), and Xiaojun Liu(刘晓峻) Chin. Phys. B, 2022, 31 (4): 044304.   DOI: 10.1088/1674-1056/ac4a6f Abstract （233）   HTML （0）    PDF （2890KB）（202）       Knowledge map    Photoacoustic imaging is a potential candidate for in vivo brain imaging, whereas, its imaging performance could be degraded by inhomogeneous multi-layered media, consisted of scalp and skull. In this work, we propose a low-artifact photoacoustic microscopy (LAPAM) scheme, which combines conventional acoustic-resolution photoacoustic microscopy with scanning acoustic microscopy to suppress the reflection artifacts induced by multi-layers. Based on similar propagation characteristics of photoacoustic signals and ultrasonic echoes, the ultrasonic echoes can be employed as the filters to suppress the reflection artifacts to obtain low-artifact photoacoustic images. Phantom experiment is used to validate the effectiveness of this method. Furthermore, LAPAM is applied for in-vivo imaging mouse brain without removing the scalp and the skull. Experimental results show that the proposed method successfully achieves the low-artifact brain image, which demonstrates the practical applicability of LAPAM. This work might improve the photoacoustic imaging quality in many biomedical applications which involve tissues with complex acoustic properties, such as brain imaging through scalp and skull.

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The 50 nm-thick yttrium iron garnet films with perpendicular magnetic anisotropy Shuyao Chen(陈姝瑶), Yunfei Xie(谢云飞), Yucong Yang(杨玉聪), Dong Gao(高栋), Donghua Liu(刘冬华), Lin Qin(秦林), Wei Yan(严巍), Bi Tan(谭碧), Qiuli Chen(陈秋丽), Tao Gong(龚涛), En Li(李恩), Lei Bi(毕磊), Tao Liu(刘涛), and Longjiang Deng(邓龙江) Chin. Phys. B, 2022, 31 (4): 048503.   DOI: 10.1088/1674-1056/ac4cc4 Abstract （240）   HTML （0）    PDF （1413KB）（190）       Knowledge map    Yttrium iron garnet (YIG) films possessing both perpendicular magnetic anisotropy (PMA) and low damping would serve as ideal candidates for high-speed energy-efficient spintronic and magnonic devices. However, it is still challenging to achieve PMA in YIG films thicker than 20 nm, which is a major bottleneck for their development. In this work, we demonstrate that this problem can be solved by using substrates with moderate lattice mismatch with YIG so as to suppress the excessive strain-induced stress release as increasing the YIG thickness. After carefully optimizing the growth and annealing conditions, we have achieved out-of-plane spontaneous magnetization in YIG films grown on sGGG substrates, even when they are as thick as 50 nm. Furthermore, ferromagnetic resonance and spin pumping induced inverse spin Hall effect measurements further verify the good spin transparency at the surface of our YIG films.

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Self-screening of the polarized electric field in wurtzite gallium nitride along [0001] direction Qiu-Ling Qiu(丘秋凌), Shi-Xu Yang(杨世旭), Qian-Shu Wu(吴千树), Cheng-Lang Li(黎城朗), Qi Zhang(张琦), Jin-Wei Zhang(张津玮), Zhen-Xing Liu(刘振兴), Yuan-Tao Zhang(张源涛), and Yang Liu(刘扬) Chin. Phys. B, 2022, 31 (4): 047103.   DOI: 10.1088/1674-1056/ac4746 Abstract （116）   HTML （0）    PDF （743KB）（88）       Knowledge map    The strong polarization effect of GaN-based materials is widely used in high-performance devices such as white-light-emitting diodes (white LEDs), high electron mobility transistors (HEMTs), and GaN polarization superjunctions. However, the current researches on the polarization mechanism of GaN-based materials are not sufficient. In this paper, we studied the influence of polarization on electric field and energy band characteristics of Ga-face GaN bulk materials by using a combination of theoretical analysis and semiconductor technology computer-aided design (TCAD) simulation. The self-screening effect in Ga-face bulk GaN under ideal and non-ideal conditions is studied respectively. We believe that the formation of high-density two-dimensional electron gas (2DEG) in GaN is the accumulation of screening charges. We also clarify the source and accumulation of the screening charges caused by the GaN self-screening effect in this paper and aim to guide the design and optimization of high-performance GaN-based devices.

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Measuring Loschmidt echo via Floquet engineering in superconducting circuits Shou-Kuan Zhao(赵寿宽), Zi-Yong Ge(葛自勇), Zhong-Cheng Xiang(相忠诚), Guang-Ming Xue(薛光明), Hai-Sheng Yan(严海生), Zi-Ting Wang(王子婷), Zhan Wang(王战), Hui-Kai Xu(徐晖凯), Fei-Fan Su(宿非凡), Zhao-Hua Yang(杨钊华), He Zhang(张贺), Yu-Ran Zhang(张煜然), Xue-Yi Guo(郭学仪), Kai Xu(许凯), Ye Tian(田野), Hai-Feng Yu(于海峰), Dong-Ning Zheng(郑东宁), Heng Fan(范桁), and Shi-Ping Zhao(赵士平) Chin. Phys. B, 2022, 31 (3): 030307.   DOI: 10.1088/1674-1056/ac40f8 Abstract （436）   HTML （0）    PDF （1107KB）（483）       Knowledge map    The Loschmidt echo is a useful diagnostic for the perfection of quantum time-reversal process and the sensitivity of quantum evolution to small perturbations. The main challenge for measuring the Loschmidt echo is the time reversal of a quantum evolution. In this work, we demonstrate the measurement of the Loschmidt echo in a superconducting 10-qubit system using Floquet engineering and discuss the imperfection of an initial Bell-state recovery arising from the next-nearest-neighbor (NNN) coupling present in the qubit device. Our results show that the Loschmidt echo is very sensitive to small perturbations during quantum-state evolution, in contrast to the quantities like qubit population that is often considered in the time-reversal experiment. These properties may be employed for the investigation of multiqubit system concerning many-body decoherence and entanglement, etc., especially when devices with reduced or vanishing NNN coupling are used.

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Electronic structure and spin–orbit coupling in ternary transition metal chalcogenides Cu2TlX2 (X = Se, Te) Na Qin(秦娜), Xian Du(杜宪), Yangyang Lv(吕洋洋), Lu Kang(康璐), Zhongxu Yin(尹中旭), Jingsong Zhou(周景松), Xu Gu(顾旭), Qinqin Zhang(张琴琴), Runzhe Xu(许润哲), Wenxuan Zhao(赵文轩), Yidian Li(李义典), Shuhua Yao(姚淑华), Yanfeng Chen(陈延峰), Zhongkai Liu(柳仲楷), Lexian Yang(杨乐仙), and Yulin Chen(陈宇林) Chin. Phys. B, 2022, 31 (3): 037101.   DOI: 10.1088/1674-1056/ac3ecd Abstract （307）   HTML （1）    PDF （5919KB）（315）       Knowledge map    Ternary transition metal chalcogenides provide a rich platform to search and study intriguing electronic properties. Using angle-resolved photoemission spectroscopy and ab initio calculation, we investigate the electronic structure of Cu$_{2}$Tl$X_{2}$ ($X=\text{Se, Te}$), ternary transition metal chalcogenides with quasi-two-dimensional crystal structure. The band dispersions near the Fermi level are mainly contributed by the Te/Se p orbitals. According to our ab-initio calculation, the electronic structure changes from a semiconductor with indirect band gap in Cu$_{2}$TlSe$_{2}$ to a semimetal in Cu$_{2}$TlTe$_{2}$, suggesting a band-gap tunability with the composition of Se and Te. By comparing ARPES experimental data with the calculated results, we identify strong modulation of the band structure by spin-orbit coupling in the compounds. Our results provide a ternary platform to study and engineer the electronic properties of transition metal chalcogenides related to large spin-orbit coupling.

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