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• REPORT
Daniele P. Anderle, Valerio Bertone, Xu Cao, Lei Chang, Ningbo Chang, Gu Chen, Xurong Chen, Zhuojun Chen, Zhufang Cui, Lingyun Dai, Weitian Deng, Minghui Ding, Xu Feng, Chang Gong, Longcheng Gui, Feng-Kun Guo, Chengdong Han, Jun He, Tie-Jiun Hou, Hongxia Huang, Yin Huang, KrešImir KumeričKi, L. P. Kaptari, Demin Li, Hengne Li, Minxiang Li, Xueqian Li, Yutie Liang, Zuotang Liang, Chen Liu, Chuan Liu, Guoming Liu, Jie Liu, Liuming Liu, Xiang Liu, Tianbo Liu, Xiaofeng Luo, Zhun Lyu, Boqiang Ma, Fu Ma, Jianping Ma, Yugang Ma, Lijun Mao, Cédric Mezrag, Hervé Moutarde, Jialun Ping, Sixue Qin, Hang Ren, Craig D. Roberts, Juan Rojo, Guodong Shen, Chao Shi, Qintao Song, Hao Sun, Paweł Sznajder, Enke Wang, Fan Wang, Qian Wang, Rong Wang, Ruiru Wang, Taofeng Wang, Wei Wang, Xiaoyu Wang, Xiaoyun Wang, Jiajun Wu, Xinggang Wu, Lei Xia, Bowen Xiao, Guoqing Xiao, Ju-Jun Xie, Yaping Xie, Hongxi Xing, Hushan Xu, Nu Xu, Shusheng Xu, Mengshi Yan, Wenbiao Yan, Wencheng Yan, Xinhu Yan, Jiancheng Yang, Yi-Bo Yang, Zhi Yang, Deliang Yao, Zhihong Ye, Peilin Yin, C.-P. Yuan, Wenlong Zhan, Jianhui Zhang, Jinlong Zhang, Pengming Zhang, Yifei Zhang, Chao-Hsi Chang, Zhenyu Zhang, Hongwei Zhao, Kuang-Ta Chao, Qiang Zhao, Yuxiang Zhao, Zhengguo Zhao, Liang Zheng, Jian Zhou, Xiang Zhou, Xiaorong Zhou, Bingsong Zou, Liping Zou
Frontiers of Physics, 2021, 16(6): 64701. https://doi.org/10.1007/s11467-021-1062-0

Lepton scattering is an established ideal tool for studying inner structure of small particles such as nucleons as well as nuclei. As a future high energy nuclear physics project, an Electron-ion collider in China (EicC) has been proposed. It will be constructed based on an upgraded heavy-ion accelerator, High Intensity heavy-ion Accelerator Facility (HIAF) which is currently under construction, together with a new electron ring. The proposed collider will provide highly polarized electrons (with a po- larization of 80%) and protons (with a polarization of 70%) with variable center of mass energies from 15 to 20 GeV and the luminosity of (2–3)×1033 cm2•s1. Polarized deuterons and Helium-3, as well as unpolarized ion beams from Carbon to Uranium, will be also available at the EicC.

The main foci of the EicC will be precision measurements of the structure of the nucleon in the sea quark region, including 3D tomography of nucleon; the partonic structure of nuclei and the parton interaction with the nuclear environment; the exotic states, especially those with heavy flavor quark contents. In addition, issues fundamental to understanding the origin of mass could be addressed by measurements of heavy quarkonia near-threshold production at the EicC. In order to achieve the above-mentioned physics goals, a hermetical detector system will be constructed with cutting-edge technologies.

This document is the result of collective contributions and valuable inputs from experts across the globe. The EicC physics program complements the ongoing scientific programs at the Jefferson Laboratory and the future EIC project in the United States. The success of this project will also advance both nuclear and particle physics as well as accelerator and detector technology in China.

• TOPICAL REVIEW
Zhican Zhou, Fengyou Yang, Shu Wang, Lei Wang, Xiaofeng Wang, Cong Wang, Yong Xie, Qian Liu
Frontiers of Physics, 2022, 17(2): 23204. https://doi.org/10.1007/s11467-021-1114-5

The rapid development of big-data analytics (BDA), internet of things (IoT) and artificial intelligent Technology (AI) demand outstanding electronic devices and systems with faster processing speed, lower power consumption, and smarter computer architecture. Memristor, as a promising Non-Volatile Memory (NVM) device, can effectively mimic biological synapse, and has been widely studied in recent years. The appearance and development of two-dimensional materials (2D material) accelerate and boost the progress of memristor systems owing to a bunch of the particularity of 2D material compared to conventional transition metal oxides (TMOs), therefore, 2D material-based memristors are called as new-generation intelligent memristors. In this review, the memristive (resistive switching) phenomena and the development of new-generation memristors are demonstrated involving grapheme (GR), transition-metal dichalcogenides (TMDs) and hexagonal boron nitride (h-BN) based memristors. Moreover, the related progress of memristive mechanisms is remarked.

• REVIEW ARTICLE
Erjun Liang, Qiang Sun, Huanli Yuan, Jiaqi Wang, Gaojie Zeng, Qilong Gao
Frontiers of Physics, 2021, 16(5): 53302. https://doi.org/10.1007/s11467-021-1070-0

Negative thermal expansion (NTE) of materials is an intriguing phenomenon challenging the concept of traditional lattice dynamics and of importance for a variety of applications. Progresses in this field develop markedly and update continuously our knowledge on the NTE behavior of materials. In this article, we review the most recent understandings on the underlying mechanisms (anharmonic phonon vibration, magnetovolume effect, ferroelectrorestriction and charge transfer) of thermal shrinkage and the development of NTE materials under each mechanism from both the theoretical and experimental aspects. Besides the low frequency optical phonons which are usually accepted as the origins of NTE in framework structures, NTE driven by acoustic phonons and the interplay between anisotropic elasticity and phonons are stressed. Based on the data documented, some problems affecting applications of NTE materials are discussed and strategies for discovering and design novel framework structured NET materials are also presented.

• RESEARCH ARTICLE
Yixin Yang, Peng Gao, Li-Chen Zhao, Zhan-Ying Yang
Frontiers of Physics, 2022, 17(3): 32503. https://doi.org/10.1007/s11467-021-1127-0

We report a kind of kink-like breathers in one-dimensional Bose–Einstein condensates (BECs) with helicoidal spin–orbit coupling (SOC), on whose two sides the background densities manifest obvious difference (called kink amplitude). The kink amplitude and shape of breather can be adjusted by the strength and period of helicoidal SOC, and its atomic number in two components exchanges periodically with time. The SOC has similar influence on the kink amplitude and the exchanged atomic number, especially when the background wave number is fixed. It indicates that the oscillating intensity of breather can be controlled by adjusting initial kink amplitude. Our work showcases the great potential of realizing novel types of breathers through SOC, and deepens our understanding on the formation mechanisms of breathers in BECs.

• RESEARCH ARTICLE
Sai Li, Pu Shen, Tao Chen, Zheng-Yuan Xue
Frontiers of Physics, 2021, 16(5): 51502. https://doi.org/10.1007/s11467-021-1087-4

High-fidelity quantum gates are essential for large-scale quantum computation. However, any quantum manipulation will inevitably affected by noises, systematic errors and decoherence effects, which lead to infidelity of a target quantum task. Therefore, implementing high-fidelity, robust and fast quantum gates is highly desired. Here, we propose a fast and robust scheme to construct high-fidelity holonomic quantum gates for universal quantum computation based on resonant interaction of three-level quantum systems via shortcuts to adiabaticity. In our proposal, the target Hamiltonian to induce noncyclic non-Abelian geometric phases can be inversely engineered with less evolution time and demanding experimentally, leading to high-fidelity quantum gates in a simple setup. Besides, our scheme is readily realizable in physical system currently pursued for implementation of quantum computation. Therefore, our proposal represents a promising way towards fault-tolerant geometric quantum computation.

• RESEARCH ARTICLE
Xiao-Feng Shi
Frontiers of Physics, 2021, 16(5): 52501. https://doi.org/10.1007/s11467-021-1069-6

Alkaline-earth-like (AEL) atoms with two valence electrons and a nonzero nuclear spin can be excited to Rydberg state for quantum computing. Typical AEL ground states possess no hyperfine splitting, but unfortunately a GHz-scale splitting seems necessary for Rydberg excitation. Though strong magnetic fields can induce a GHz-scale splitting, weak fields are desirable to avoid noise in experiments. Here, we provide two solutions to this outstanding challenge with realistic data of well-studied AEL isotopes. In the first theory, the two nuclear spin qubit states |0〉 and |1〉 are excited to Rydberg states |r〉 with detuning Δ and 0, respectively, where a MHz-scale detuning Δ arises from a weak magnetic field on the order of 1 G. With a proper ratio between Δ and Ω, the qubit state |1〉 can be fully excited to the Rydberg state while |0〉 remains there. In the second theory, we show that by choosing appropriate intermediate states a two-photon Rydberg excitation can proceed with only one nuclear spin qubit state. The second theory is applicable whatever the magnitude of the magnetic field is. These theories bring a versatile means for quantum computation by combining the broad applicability of Rydberg blockade and the incomparable advantages of nuclear-spin quantum memory in two-electron neutral atoms.

• RESEARCH ARTICLE
Zun-Lei Xu, Kai-Kai Duan, Wei Jiang, Shi-Jun Lei, Xiang Li, Zhao-Qiang Shen, Tao Ma, Meng Su, Qiang Yuan, Chuan Yue, Yi-Zhong Fan, Jin Chang
Frontiers of Physics, 2022, 17(3): 34501. https://doi.org/10.1007/s11467-021-1121-6

The DArk Matter Particle Explorer (DAMPE) is a space high-energy cosmic-ray detector covering a wide energy band with a high energy resolution. One of the key scientific goals of DAMPE is to carry out indirect detection of dark matter by searching for high-energy gamma-ray line structure. To promote the sensitivity of gamma-ray line search with DAMPE, it is crucial to improve the acceptance and energy resolution of gamma-ray photons. In this paper, we quantitatively proved that the photon sample with the largest ratio of acceptance to energy resolution is optimal for line search. We therefore developed a line-search sample specifically optimized for the line-search. Meanwhile, in order to increase the statistics, we also selected the so-called BGO-only photons that convert into e+e- pairs only in the BGO calorimeter. The standard, the line-search, and the BGO-only photon samples are then tested for line-search individually and collectively. The results show that a significantly improved limit could be obtained from an appropriate combination of the date sets, and the increase is about 20% for the highest case compared with using the standard sample only.

• RESEARCH ARTICLE
Na-Na Zhang (张娜娜), Ming-Jie Tao (陶明杰), Wan-Ting He (何宛亭), Xin-Yu Chen (陈鑫宇), Xiang-Yu Kong (孔祥宇), Fu-Guo Deng (邓富国), Neill Lambert, Qing Ai (艾清)
Frontiers of Physics, 2021, 16(5): 51501. https://doi.org/10.1007/s11467-021-1064-y

Simulation of open quantum dynamics for various Hamiltonians and spectral densities are ubiquitous for studying various quantum systems. On a quantum computer, only log2N qubits are required for the simulation of an N-dimensional quantum system, hence simulation in a quantum computer can greatly reduce the computational complexity compared with classical methods. Recently, a quantum simulation approach was proposed for studying photosynthetic light harvesting [npj Quantum Inf. 4, 52 (2018)]. In this paper, we apply the approach to simulate the open quantum dynamics of various photosynthetic systems. We show that for Drude–Lorentz spectral density, the dimerized geometries with strong couplings within the donor and acceptor clusters respectively exhibit significantly improved efficiency. We also demonstrate that the overall energy transfer can be optimized when the energy gap between the donor and acceptor clusters matches the optimum of the spectral density. The effects of different types of baths, e.g., Ohmic, sub-Ohmic, and super-Ohmic spectral densities are also studied. The present investigations demonstrate that the proposed approach is universal for simulating the exact quantum dynamics of photosynthetic systems.

• VIEW & PERSPECTIVE
Kim Siang Khaw, Liang Li, Jing Shu
Frontiers of Physics, 2021, 16(6): 64602. https://doi.org/10.1007/s11467-021-1089-2

The first results from the Fermilab Muon g–2 Experiment shed lights on the mystery surrounding the magnetic anomaly of the muon. This could become a window into a new era of particle physics.

• VIEW & PERSPECTIVE
Lena Du, Zhongchang Wang, Guozhong Zhao
Frontiers of Physics, 2022, 17(2): 23602. https://doi.org/10.1007/s11467-022-1152-7

Two-dimensional (2D) materials with atomic thickness, non-volatile resistive switching feature and compatibility with the semiconducting technology are naturally a good media of memristors. 2D materials-based memristors with excellent performance, low-power consumption and high integration density can be integrated with other circuit components to implement the complicate logic computing, which will become a key driving force for the development of artificial intelligence.

• TOPICAL REVIEW
Si-Yu Li, Lin He
Frontiers of Physics, 2022, 17(3): 33201. https://doi.org/10.1007/s11467-021-1125-2

Graphene quantum dots (GQDs) not only have potential applications on spin qubit, but also serve as essential platforms to study the fundamental properties of Dirac fermions, such as Klein tunneling and Berry phase. By now, the study of quantum confinement in GQDs still attract much attention in condensed matter physics. In this article, we review the experimental progresses on quantum confinement in GQDs mainly by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Here, the GQDs are divided into Klein GQDs, bound-state GQDs and edge-terminated GQDs according to their different confinement strength. Based on the realization of quasi-bound states in Klein GQDs, external perpendicular magnetic field is utilized as a manipulation approach to trigger and control the novel properties by tuning Berry phase and electron–electron (e–e) interaction. The tip-induced edge-free GQDs can serve as an intuitive mean to explore the broken symmetry states at nanoscale and single-electron accuracy, which are expected to be used in studying physical properties of different two-dimensional materials. Moreover, high-spin magnetic ground states are successfully introduced in edge-terminated GQDs by designing and synthesizing triangulene zigzag nanographenes.

• TOPICAL REVIEW
Jiahao Fan, Huaqing Huang
Frontiers of Physics, 2022, 17(1): 13203. https://doi.org/10.1007/s11467-021-1100-y

With the rapid development of topological states in crystals, the study of topological states has been extended to quasicrystals in recent years. In this review, we summarize the recent progress of topological states in quasicrystals, particularly focusing on one-dimensional (1D) and 2D systems. We first give a brief introduction to quasicrystalline structures. Then, we discuss topological phases in 1D quasicrystals where the topological nature is attributed to the synthetic dimensions associated with the quasiperiodic order of quasicrystals. We further present the generalization of various types of crystalline topological states to 2D quasicrystals, where real-space expressions of corresponding topological invariants are introduced due to the lack of translational symmetry in quasicrystals. Finally, since quasicrystals possess forbidden symmetries in crystals such as five-fold and eight-fold rotation, we provide an overview of unique quasicrystalline symmetry-protected topological states without crystalline counterpart.

• VIEW & PERSPECTIVE
Qingquan Kong, Xuguang An, Jing Zhang, Weitang Yao, Chenghua Sun
Frontiers of Physics, 2022, 17(4): 43601. https://doi.org/10.1007/s11467-022-1183-0

Searching for high-performance and cost-effective catalysts is of particular importance for the practical electrocatalysis applications. The heterojunctions with components in different dimensions show unique physical and chemical properties, which can offer large space for rational design of electrocatalysts. In this paper, we firstly reviewed recently related works, and then proposed a few perspectives on exploring heterojunction for electrocatalysis applications.

• RESEARCH ARTICLE
Annan Fan, Shi-Dong Liang
Frontiers of Physics, 2022, 17(3): 33501. https://doi.org/10.1007/s11467-021-1122-5

Non-Hermitian systems as theoretical models of open or dissipative systems exhibit rich novel physical properties and fundamental issues in condensed matter physics. We propose a generalized local–global correspondence between the pseudo-boundary states in the complex energy plane and topological invariants of quantum states. We find that the patterns of the pseudo-boundary states in the complex energy plane mapped to the Brillouin zone are topological invariants against the parameter deformation. We demonstrate this approach by the non-Hermitian Chern insulator model. We give the consistent topological phases obtained from the Chern number and vorticity. We also find some novel topological invariants embedded in the topological phases of the Chern insulator model, which enrich the phase diagram of the non-Hermitian Chern insulators model beyond that predicted by the Chern number and vorticity. We also propose a generalized vorticity and its flipping index to understand physics behind this novel local–global correspondence and discuss the relationships between the local–global correspondence and the Chern number as well as the transformation between the Brillouin zone and the complex energy plane. These novel approaches provide insights to how topological invariants may be obtained from local information as well as the global property of quantum states, which is expected to be applicable in more generic non-Hermitian systems.

• RESEARCH ARTICLE
Qingquan Kong, Xuguang An, Lin Huang, Xiaolian Wang, Wei Feng, Siyao Qiu, Qingyuan Wang, Chenghua Sun
Frontiers of Physics, 2021, 16(5): 53506. https://doi.org/10.1007/s11467-021-1066-9

Heterojunction structure has been extensively employed for the design of novel catalysts. In the present study, density functional theory was utilized to investigate the electronic structure and hydrogen evolution performance of Ti3C2O2 MXene quantum dots/graphene (QDs/G) heterostructure. Results show that a slight distortion can be observed in graphene after hybriding with QDs, due to which the electronic structure of QDs have been changed. Associated with such QDs-graphene interaction, the catalytic activity of Ti3C2O2 QDs has been optimized, leading to excellent HER catalytic performance.

• RESEARCH ARTICLE
Lei Qiao, Ning-hua Wu, Tianhao Li, Siqi Wu, Zhuyi Zhang, Miaocong Li, Jiang Ma, Baijiang Lv, Yupeng Li, Chenchao Xu, Qian Tao, Chao Cao, Guang-Han Cao, Zhu-An Xu
Frontiers of Physics, 2021, 16(6): 63501. https://doi.org/10.1007/s11467-021-1076-7

We investigated the coexistence of superconductivity and antiferromagnetic order in the compound Er2O2Bi with anti-ThCr2Si2-type structure through resistivity, magnetization, specific heat measurements and first-principle calculations. The superconducting transition temperature Tc of 1.23 K and antiferromagnetic transition temperature TN of 3 K are observed in the sample with the best nominal composition. The superconducting upper critical field Hc2(0) and electron-phonon coupling constant λeph in Er2O2Bi are similar to those in the previously reported non-magnetic superconductor Y2O2Bi with the same structure, indicating that the superconductivity in Er2O2Bi may have the same origin as in Y2O2Bi. The first-principle calculations of Er2O2Bi show that the Fermi surface is mainly composed of the Bi 6p orbitals both in the paramagnetic and antiferromagnetic state, implying minor effect of the 4f electrons on the Fermi surface. Besides, upon increasing the oxygen incorporation in Er2OxBi, Tc increases from 1 to 1.23 K and TN decreases slightly from 3 K to 2.96 K, revealing that superconductivity and antiferromagnetic order may compete with each other. The Hall effect measurements indicate that hole-type carrier density indeed increases with increasing oxygen content, which may account for the variations of Tc and TN with different oxygen content.

• RESEARCH ARTICLE
Yu-Cheng Chen, Ming Gong, Peng Xue, Hai-Dong Yuan, Cheng-Jie Zhang
Frontiers of Physics, 2021, 16(5): 53601. https://doi.org/10.1007/s11467-021-1063-z

In conventional quantum mechanics, quantum no-deleting and no-cloning theorems indicate that two different and nonorthogonal states cannot be perfectly and deterministically deleted and cloned, respectively. Here, we investigate the quantum deleting and cloning in a pseudo-unitary system. We first present a pseudo-Hermitian Hamiltonian with real eigenvalues in a two-qubit system. By using the pseudo-unitary operators generated from this pseudo-Hermitian Hamiltonian, we show that it is possible to delete and clone a class of two different and nonorthogonal states, and it can be generalized to arbitrary two different and nonorthogonal pure qubit states. Furthermore, state discrimination, which is strongly related to quantum no-cloning theorem, is also discussed. Last but not least, we simulate the pseudo-unitary operators in conventional quantum mechanics with post-selection, and obtain the success probability of simulations. Pseudo-unitary operators are implemented with a limited efficiency due to the post-selections. Thus, the success probabilities of deleting and cloning in the simulation by conventional quantum mechanics are less than unity, which maintain the quantum no-deleting and no-cloning theorems.

• REVIEW ARTICLE
Aviv Karnieli, Yongyao Li, Ady Arie
Frontiers of Physics, 2022, 17(1): 12301. https://doi.org/10.1007/s11467-021-1102-9

The geometric phase of light has been demonstrated in various platforms of the linear optical regime, raising interest both for fundamental science as well as applications, such as flat optical elements. Recently, the concept of geometric phases has been extended to nonlinear optics, following advances in engineering both bulk nonlinear photonic crystals and nonlinear metasurfaces. These new technologies offer a great promise of applications for nonlinear manipulation of light. In this review, we cover the recent theoretical and experimental advances in the field of geometric phases accompanying nonlinear frequency conversion. We first consider the case of bulk nonlinear photonic crystals, in which the interaction between propagating waves is quasi-phase-matched, with an engineerable geometric phase accumulated by the light. Nonlinear photonic crystals can offer efficient and robust frequency conversion in both the linearized and fully-nonlinear regimes of interaction, and allow for several applications including adiabatic mode conversion, electromagnetic nonreciprocity and novel topological effects for light. We then cover the rapidly-growing field of nonlinear Pancharatnam-Berry metasurfaces, which allow the simultaneous nonlinear generation and shaping of light by using ultrathin optical elements with subwavelength phase and amplitude resolution. We discuss the macroscopic selection rules that depend on the rotational symmetry of the constituent meta-atoms, the order of the harmonic generations, and the change in circular polarization. Continuous geometric phase gradients allow the steering of light beams and shaping of their spatial modes. More complex designs perform nonlinear imaging and multiplex nonlinear holograms, where the functionality is varied according to the generated harmonic order and polarization. Recent advancements in the fabrication of three dimensional nonlinear photonic crystals, as well as the pursuit of quantum light sources based on nonlinear metasurfaces, offer exciting new possibilities for novel nonlinear optical applications based on geometric phases.

• RESEARCH ARTICLE
Jing-Kai Fang, Jun-Han Huang, Han-Qing Wu, Dao-Xin Yao
Frontiers of Physics, 2022, 17(3): 33503. https://doi.org/10.1007/s11467-021-1124-3

By using Lanczos exact diagonalization and quantum Monte Carlo combined with stochastic analytic continuation, we study the dynamical properties of the S = 1 antiferromagnetic Heisenberg chain with different strengths of bond disorder. In the weak disorder region, we find weakly coupled bonds which can induce additional low-energy excitation below the one-magnon mode. As the disorder increases, the average Haldane gap closes at δ ~ 0.5 with more and more low-energy excitations coming out. After the critical disorder strength δc ~ 1, the system reaches a random-singlet phase with prominent sharp peak at ω = 0 and broad continuum at ω > 0 of the dynamic spin structure factor. In addition, we analyze the distribution of random spin domains and numerically find three kinds of domains hosting effective spin-1/2 quanta or spin-1 sites in between. These “spins” can form the weakly coupled longrange singlets due to quantum fluctuation which contribute to the sharp peak at ω = 0.

• RESEARCH ARTICLE
Qing-Hua Ke, Yue-Ming Zhou, Yi-Jie Liao, Jin-Tai Liang, Yong Zhao, Jia Tan, Min Li, Pei-Xiang Lu
Frontiers of Physics, 2021, 16(5): 52503. https://doi.org/10.1007/s11467-021-1084-7

By numerically solving the three-dimensional time-dependent Schrödinger equation, we have invest-tigated multiphoton ionization of hydrogen atom in the two-color circularly polarized (TCCP) laser fields consisting of a strong 400 nm and a much weaker 800 nm pulses. Due to the presence of perturb-bative 800 nm laser pulse, sideband peaks emerge between the above-threshold ionization rings in the photoelectron momentum distributions. Our numerical results show that the sideband peaks exhibit one-lobe structure in the co-rotating TCCP laser fields, while it displays the three-lobe structure in the counter-rotating TCCP laser fields. Moreover, the photoelectron yield of sidebands in the co-rotating TCCP fields is much higher than those of the counter-rotating TCCP fields. These phenomena could be well explained from the perspective of the photon-absorption channels via the selection rules. In-terestingly, an obvious phase shift between the sidebands of different orders from the co-rotating and counter-rotating TCCP fields is observed. This shift indicates the helicity-dependent time delay in the one-photon continuum-continuum transition process.

• RESEARCH ARTICLE
Peng-Hong Lu, Xiao-Fei Zhang, Chao-Qing Dai
Frontiers of Physics, 2022, 17(4): 42501. https://doi.org/10.1007/s11467-021-1134-1

We consider the dynamics and formation of vortices from ring dark solitons in a two-dimensional Bose–Einstein condensate with the Rashba spin–orbit coupling based on the time-dependent coupled Gross–Pitaevskii equation. Compared with previous results, the system exhibits complex dynamical behaviors in the presence of the spin–orbit coupling. With the modulation of the spin–orbit coupling, not only the lifetime of ring dark solitons is greatly prolonged, but also their attenuation kinetics is significantly affected. For two shallow ring dark solitons with the equal strength of the spin–orbit coupling, the radius of ring dark solitons increases to a maximum value over time and then shrinks into a minimum value. Due to the effect of the snake instability, ring dark solitons split into a series of ring-like clusters of vortex pairs, which perform complex oscillations. This indicates that the system is strongly dependent on the presence of the spin–orbit coupling. Furthermore, the effect of different initial modulation depths on the dynamics of ring dark solitons is investigated.

• RESEARCH ARTICLE
Xiao-Dong Zhang, Kang Liu, Jun-Wei Fu, Hong-Mei Li, Hao Pan, Jun-Hua Hu, Min Liu
Frontiers of Physics, 2021, 16(6): 63500. https://doi.org/10.1007/s11467-021-1079-4

Electrocatalytic CO2 reduction reaction (CO2RR) to obtain C2 products has drawn widespread attentions. Copper-based materials are the most reported catalysts for CO2 reduction to C2 products. Design of high-efficiency pseudo-copper catalysts according to the key characteristics of copper (Cu) is an important strategy to understand the reaction mechanism of C2 products. In this work, density function theory (DFT) calculations are used to predict nickel–zinc (NiZn) alloy catalysts with the criteria similar structure and intermediate adsorption property to Cu catalyst. The calculated tops of 3d states of NiZn3(001) catalysts are the same as Cu(100), which is the key parameter affecting the adsorption of intermediate products. As a result, NiZn3(001) exhibits similar adsorption properties with Cu(100) on the crucial intermediates *CO2, *CO and *H. Moreover, we further studied CO formation, CO hydrogenation and C–C coupling process on Ni–Zn alloys. The free energy profile of C2 products formation shows that the energy barrier of C2 products formation on NiZn3(001) is even lower than Cu(100). These results indicate that NiZn3 alloy as pseudo-copper catalyst can exhibit a higher catalytic activity and selectivity of C2 products during CO2RR. This work proposes a feasible pseudo-copper catalyst and provides guidance to design high-efficiency catalysts for CO2RR to C2 or multi-carbon products.

• RESEARCH ARTICLE
Jun-Yi Qu, Ming Tang, Ying Liu, Shu-Guang Guan
Frontiers of Physics, 2021, 16(5): 51503. https://doi.org/10.1007/s11467-021-1082-9

The reversible spreading processes with repeated infection widely exist in nature and human society, such as gonorrhea propagation and meme spreading. Identifying influential spreaders is an important issue in the reversible spreading dynamics on complex networks, which has been given much attention. Except for structural centrality, the nodes’ dynamical states play a significant role in their spreading influence in the reversible spreading processes. By integrating the number of outgoing edges and infection risks of node’s neighbors into structural centrality, a new measure for identifying influential spreaders is articulated which considers the relative importance of structure and dynamics on node influence. The number of outgoing edges and infection risks of neighbors represent the positive effect of the local structural characteristic and the negative effect of the dynamical states of nodes in identifying influential spreaders, respectively. We find that an appropriate combination of these two characteristics can greatly improve the accuracy of the proposed measure in identifying the most influential spreaders. Notably, compared with the positive effect of the local structural characteristic, slightly weakening the negative effect of dynamical states of nodes can make the proposed measure play the best performance. Quantitatively understanding the relative importance of structure and dynamics on node influence provides a significant insight into identifying influential nodes in the reversible spreading processes.

• VIEW & PERSPECTIVE
Mai Tal, Danielle Ben Haim, Tal Ellenbogen
Frontiers of Physics, 2022, 17(1): 12302. https://doi.org/10.1007/s11467-021-1123-4
• RESEARCH ARTICLE
Wenyu Sun, Tong Liu, Maoqiang Jing, Liangliang Wang, Bin Zhong, Weimin Song
Frontiers of Physics, 2021, 16(6): 64501. https://doi.org/10.1007/s11467-021-1085-6

Initial State Radiation (ISR) plays an important role in e+e collision experiments such as the BESIII. To correct the ISR effects in measurements of hadronic cross-sections of e+e annihilation, an iterative method that weights simulated ISR events is proposed here to assess the efficiency of event selection and the ISR correction factor for the observed cross-section. The simulated ISR events were generated only once, and the obtained cross-sectional line shape was used iteratively to weigh the same simulated ISR events to evaluate the efficiency and corrections until the results converge. Compared with the method of generating ISR events iteratively, the proposed weighting method provides consistent results, and reduces the computational time and disk space required by a factor of five or more, thus speeding-up e+e hadronic cross-section measurements.

• PERSPECTIVE
Changqing Xiang, Cheng-Wei Wu, Wu-Xing Zhou, Guofeng Xie, Gang Zhang
Frontiers of Physics, 2022, 17(1): 13202. https://doi.org/10.1007/s11467-021-1090-9

In recent years, lithium ion (Li-ion) batteries have served as significant power sources in portable electronic devices and electric vehicles because of their high energy density and rate capability. There are growing concerns towards the safety of Li-ion batteries, in which thermal conductivities of anodes, cathodes, electrolytes and separator play key roles for determining the thermal energy transport in Li-ion battery. In this review, we summarize the state-of-the-art studies on the thermal conductivities of commonly used anodes, cathodes, electrolytes and separator in Li-ion batteries, including both theoretical and experimental reports. First, the thermal conductivities of anodes and cathodes are discussed, and the effects of delithiation degree and temperature of materials are also discussed. Then, we review the thermal conductivities of commonly used electrolytes, especially on solid electrolytes. Finally, the basic concept of interfacial thermal conductance and simulation methods are presented, as well as the interfacial thermal conductance between separator and cathodes. This perspective review would provide atomic perspective knowledge to understand thermal transport in Li-ion battery, which will be beneficial to the thermal management and temperature control in electrochemical energy storage devices.

• RESEARCH ARTICLE
Na Kang, Wenhui Wan, Yanfeng Ge, Yong Liu
Frontiers of Physics, 2021, 16(6): 63506. https://doi.org/10.1007/s11467-021-1088-3

In this paper, we systematically investigated the structural and magnetic properties of CrTe by combining particle swarm optimization algorithm and first-principles calculations. By considering the electronic correlation effect, we predicted the ground-state structure of CrTe to be NiAs-type (space group P63/mmc) structure at ambient pressure, consistent with the experimental observation. Moreover, we found two extra meta-stable Cmcaand $R3 ¯m$ structures which have negative formation enthalpy and stable phonon dispersion at ambient pressure. The Cmcastructure is a layered antiferromagnetic metal. The cleaved energy of a single layer is 0.464 J/m2 , indicating the possible synthesis of CrTe monolayer. The $R3 ¯m$ structure is a ferromagnetic half-metal. When external pressure is applied, the ground-state structure of CrTe transitions from P63/mmc structure to $R3 ¯m$ structure at a pressure of 34 GPa, then to $R3 ¯m$ structure at 42 GPa. We thought these results help to motivate experimental studies of the CrTe compounds in the application of spintronics.

• RESEARCH ARTICLE
Qi-Ping Su, Hanyu Zhang, Chui-Ping Yang
Frontiers of Physics, 2021, 16(6): 61501. https://doi.org/10.1007/s11467-021-1098-1

We present a way to transfer maximally- or partially-entangled states of n single-photon-state (SPS) qubits onto ncoherent-state (CS) qubits, by employing 2nmicrowave cavities coupled to a superconducting flux qutrit. The two logic states of a SPS qubit here are represented by the vacuum state and the single-photon state of a cavity, while the two logic states of a CS qubit are encoded with two coherent states of a cavity. Because of using only one superconducting qutrit as the coupler, the circuit architecture is significantly simplified. The operation time for the state transfer does not increase with the increasing of the number of qubits. When the dissipation of the system is negligible, the quantum state can be transferred in a deterministic way since no measurement is required. Furthermore, the higher-energy intermediate level of the coupler qutrit is not excited during the entire operation and thus decoherence from the qutrit is greatly suppressed. As a specific example, we numerically demonstrate that the high-fidelity transfer of a Bell state of two SPS qubits onto two CS qubits is achievable within the present-day circuit QED technology. Finally, it is worthy to note that when the dissipation is negligible, entangled states of n CS qubits can be transferred back onto n SPS qubits by performing reverse operations. This proposal is quite general and can be extended to accomplish the same task, by employing a natural or artificial atom to couple 2nmicrowave or optical cavities.

• TOPICAL REVIEW
Zi Wang, Luqin Wang, Jiangzhi Chen, Chen Wang, Jie Ren
Frontiers of Physics, 2022, 17(1): 13201. https://doi.org/10.1007/s11467-021-1095-4

The second law of thermodynamics dictates that heat simultaneously flows from the hot to cold bath on average. To go beyond this picture, a range of works in the past decade show that, other than the average dynamical heat flux determined by instantaneous thermal bias, a non-trivial flux contribution of intrinsic geometric origin is generally present in temporally driven systems. This additional heat flux provides a free lunch for the pumped heat and could even drive heat against the bias. We review here the emergence and development of this so called “geometric heat pump”, originating from the topological geometric phase effect, and cover various quantum and classical transport systems with different internal dynamics. The generalization from the adiabatic to the non-adiabatic regime and the application of control theory are also discussed. Then, we briefly discuss the symmetry restriction on the heat pump effect, such as duality, supersymmetry and time-reversal symmetry. Finally, we examine open problems concerning the geometric heat pump process and elucidate their prospective significance in devising thermal machines with high performance.

• RESEARCH ARTICLE
Guoyu Luo, Xinyu Lv, Lu Wen, Zhiqiang Li, Zhenbing Dai
Frontiers of Physics, 2022, 17(2): 23502. https://doi.org/10.1007/s11467-021-1146-x

We theoretically study the band structures and the valley Chern numbers of the AB–AB and AB–BA stacked twisted double bilayer graphene under heterostrain effect. In the absence of heterostrain, due to the constrains by the spatial symmetries, the central two flat bands of the AB–AB are topological trivial bands, while in the AB–BA they have a finite Chern number. The heterostrain breaks all the point group symmetries and the constrains are lifted, hence the topological properties of the two arrangements can be tuned by different strain magnitudes ϵ and directions ϕ. The heterostrain has dissimilar impacts on the Chern numbers of the AB–AB and AB–BA, owing to their different band gaps, and these gaps can be modified by a vertical electric field. Our results show that the topological transitions for both arrangements occur in the ϵ range of 0.1%–0.4%, which can be realized in the graphene-based sample.