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An overview of quantum error mitigation formulas Dayue Qin(秦大粤), Xiaosi Xu(徐晓思), and Ying Li(李颖) Chin. Phys. B, 2022, 31 (9): 090306.   DOI: 10.1088/1674-1056/ac7b1e Abstract （686）   HTML （6）    PDF （953KB）（1927）       Knowledge map    Minimizing the effect of noise is essential for quantum computers. The conventional method to protect qubits against noise is through quantum error correction. However, for current quantum hardware in the so-called noisy intermediate-scale quantum (NISQ) era, noise presents in these systems and is too high for error correction to be beneficial. Quantum error mitigation is a set of alternative methods for minimizing errors, including error extrapolation, probabilistic error cancellation, measurement error mitigation, subspace expansion, symmetry verification, virtual distillation, etc. The requirement for these methods is usually less demanding than error correction. Quantum error mitigation is a promising way of reducing errors on NISQ quantum computers. This paper gives a comprehensive introduction to quantum error mitigation. The state-of-art error mitigation methods are covered and formulated in a general form, which provides a basis for comparing, combining and optimizing different methods in future work.

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Developing improved measures of non-Gaussianity and Gaussianity for quantum states based on normalized Hilbert-Schmidt distance Shaohua Xiang(向少华), Shanshan Li(李珊珊), and Xianwu Mi(米贤武) Chin. Phys. B, 2023, 32 (5): 050309.   DOI: 10.1088/1674-1056/acb0bd Abstract （263）   HTML （3）    PDF （1151KB）（1792）       Knowledge map    Non-Gaussianity of quantum states is a very important source for quantum information technology and can be quantified by using the known squared Hilbert-Schmidt distance recently introduced by Genoni et al. (Phys. Rev. A 78 042327 (2007)). It is, however, shown that such a measure has many imperfects such as the lack of the swapping symmetry and the ineffectiveness evaluation of even Schrödinger-cat-like states with small amplitudes. To deal with these difficulties, we propose an improved measure of non-Gaussianity for quantum states and discuss its properties in detail. We then exploit this improved measure to evaluate the non-Gaussianities of some relevant single-mode non-Gaussian states and multi-mode non-Gaussian entangled states. These results show that our measure is reliable. We also introduce a modified measure for Gaussianity following Mandilara and Cerf (Phys. Rev. A 86 030102(R) (2012)) and establish a conservation relation of non-Gaussianity and Gaussianity of a quantum state.

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Recent advances of interface engineering in inverted perovskite solar cells Shiqi Yu(余诗琪), Zhuang Xiong(熊壮), Zhenhan Wang(王振涵), Haitao Zhou(周海涛), Fei Ma(马飞), Zihan Qu(瞿子涵), Yang Zhao(赵洋), Xinbo Chu(楚新波), and Jingbi You(游经碧) Chin. Phys. B, 2022, 31 (10): 107307.   DOI: 10.1088/1674-1056/ac8e9f Abstract （534）   HTML （8）    PDF （8178KB）（1702）       Knowledge map    Perovskite solar cells (PSCs) have witnessed great achievement in the past decade. Most of previous researches focus on the n—i—p structure of PSCs with ultra-high efficiency. While the n—i—p devices usually used the unstable charge transport layers, such as the hygroscopic doped spiro-OMeTAD, which affect the long-term stability. The inverted device with the p—i—n structure owns better stability when using stable undoped organic molecular or metal oxide materials. There are significant progresses in inverted PSCs, most of them related to charge transport or interface engineering. In this review, we will mainly summarize the inverted PSCs progresses related to the interface engineering. After that, we prospect the future direction on inverted PSCs.

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Development of a cryogen-free dilution refrigerator Zhongqing Ji(姬忠庆), Jie Fan(樊洁), Jing Dong(董靖), Yongbo Bian(边勇波), and Zhi-Gang Cheng(程智刚) Chin. Phys. B, 2022, 31 (12): 120703.   DOI: 10.1088/1674-1056/ac9042 Abstract （763）   HTML （11）    PDF （1053KB）（1207）       Knowledge map    With thermal fluctuation strongly suppressed, low temperature environment is essential for studies of condensed matter physics and developments of quantum technologies. Ultra-low temperature below 20 mK has demonstrated its importance and significance in physical sciences and information techniques. Dilution refrigeration is by far the best feasible and reliable method to generate and keep lattice temperature in this range. With a potential shortage of helium supply, cryogen-free dilution refrigerator (CFDR), eliminating the necessity of regular helium refill, becomes the main facility for the purpose of creating ultralow temperature environments. Here we describe our successful construction of a CFDR which reached a base temperature of around 10.9 mK for continuous circulation and 8.6 mK for single-shot operation. We describe its operating mechanism and the designs of key components, especially some unique designs including heat switch and alumina thermal link. Possible improvements in the future are also discussed.

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Parallel optimization of underwater acoustic models: A survey Zi-jie Zhu(祝子杰), Shu-qing Ma(马树青), Xiao-Qian Zhu(朱小谦), Qiang Lan(蓝强), Sheng-Chun Piao(朴胜春), and Yu-Sheng Cheng(程玉胜) Chin. Phys. B, 2022, 31 (10): 104301.   DOI: 10.1088/1674-1056/ac7ccc Abstract （540）   HTML （5）    PDF （1765KB）（1191）       Knowledge map    Underwater acoustic models are effective tools for simulating underwater sound propagation. More than 50 years of research have been conducted on the theory and computational models of sound propagation in the ocean. Unfortunately, underwater sound propagation models were unable to solve practical large-scale three-dimensional problems for many years due to limited computing power and hardware conditions. Since the mid-1980s, research on high performance computing for acoustic propagation models in the field of underwater acoustics has flourished with the emergence of high-performance computing platforms, enabling underwater acoustic propagation models to solve many practical application problems that could not be solved before. In this paper, the contributions of research on high-performance computing for underwater acoustic propagation models since the 1980s are thoroughly reviewed and the possible development directions for the future are outlined.

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Superconductivity and unconventional density waves in vanadium-based kagome materials AV3Sb5 Hui Chen(陈辉), Bin Hu(胡彬), Yuhan Ye(耶郁晗), Haitao Yang(杨海涛), and Hong-Jun Gao(高鸿钧) Chin. Phys. B, 2022, 31 (9): 097405.   DOI: 10.1088/1674-1056/ac7f95 Abstract （724）   HTML （6）    PDF （6290KB）（850）       Knowledge map    Recently, the discovery of vanadium-based kagome metal AV3Sb5 (A= K, Rb, Cs) has attracted great interest in the field of superconductivity due to the coexistence of superconductivity, non-trivial surface state and multiple density waves. In this topical review, we present recent works of superconductivity and unconventional density waves in vanadium-based kagome materials AV3Sb5. We start with the unconventional charge density waves, which are thought to correlate to the time-reversal symmetry-breaking orders and the unconventional anomalous Hall effects in AV3Sb5. Then we discuss the superconductivity and the topological band structure. Next, we review the competition between the superconductivity and charge density waves under different conditions of pressure, chemical doping, thickness, and strains. Finally, the experimental evidence of pseudogap pair density wave is discussed.

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Current sensor based on diamond nitrogen-vacancy color center Zi-Yang Shi(史子阳), Wei Gao(高伟), Qi Wang(王启), Hao Guo(郭浩), Jun Tang(唐军), Zhong-Hao Li(李中豪), Huan-Fei Wen(温焕飞), Zong-Min Ma(马宗敏), and Jun Liu(刘俊) Chin. Phys. B, 2023, 32 (7): 070704.   DOI: 10.1088/1674-1056/acc3fe Abstract （416）   HTML （9）    PDF （1692KB）（837）       Knowledge map    High precision current measurement is very important for the calibration of various high-precision equipment and the measurement of other precision detection fields. A new current sensor based on diamond nitrogen-vacancy (NV) color center magnetic measurement method is proposed to realize the accurate measurement of current. This new current method can greatly improve the accuracy of current measurement. Experiments show that the linearity of the current sensor based on diamond NV color center can reach up to 33 ppm, which is superior to other current sensors and solves the problem of low linearity. When the range of input current is 5-40 A, the absolute error of the calculated current is less than 51 μA, and the relative error is 2.42×10-6 at 40 A. Combined with the research content and results of the experiment, the application of the current sensor in the field of current precision measurement is prospected.

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The application of quantum coherence as a resource Si-Yuan Liu(刘思远) and Heng Fan(范桁) Chin. Phys. B, 2023, 32 (11): 110304.   DOI: 10.1088/1674-1056/acfa85 Abstract （327）   HTML （6）    PDF （871KB）（813）       Knowledge map    Quantum coherence is a basic concept in quantum mechanics, representing one of the most fundamental characteristics that distinguishes quantum mechanics from classical physics. Quantum coherence is the basis for multi-particle interference and quantum entanglement. It is also the essential ingredient for various physical phenomena in quantum optics, quantum information, etc. In recent years, with the proposal of a quantum coherence measurement scheme based on a resource theory framework, quantum coherence as a quantum resource has been extensively investigated. This article reviews the resource theories of quantum coherence and introduces the important applications of quantum coherence in quantum computing, quantum information, and interdisciplinary fields, particularly in quantum thermodynamics and quantum biology. Quantum coherence and its applications are still being explored and developed. We hope this review can provide inspiration for relevant research.

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Thermoelectric generators and their applications: Progress, challenges, and future prospects Nassima Radouane Chin. Phys. B, 2023, 32 (5): 057307.   DOI: 10.1088/1674-1056/aca5fd Abstract （353）   HTML （2）    PDF （2763KB）（809）       Knowledge map    Our community currently deals with issues such as rising electricity costs, pollution, and global warming. Scientists work to improve energy harvesting-based power generators in order to reduce their impacts. The Seebeck effect has been used to illustrate the capacity of thermoelectric generators (TEGs) to directly convert thermal energy to electrical energy. They are also ecologically beneficial since they do not include chemical products, function quietly because they lack mechanical structures and/or moving components, and may be built using different fabrication technologies such as three-dimentional (3D) printing, silicon technology, and screen printing, etc. TEGs are also position-independent and have a long operational lifetime. TEGs can be integrated into bulk and flexible devices. This review gives further investigation of TEGs, beginning with a full discussion of their operating principle, kinds, materials utilized, figure of merit, and improvement approaches, which include various thermoelectric material arrangements and utilised technologies. This paper also discusses the use of TEGs in a variety of disciplines such as automobile and biomedical.

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Finesse measurement for high-power optical enhancement cavity Xin-Yi Lu(陆心怡), Xing Liu(柳兴), Qi-Li Tian(田其立), Huan Wang(王焕), Jia-Jun Wang(汪嘉俊), and Li-Xin Yan(颜立新) Chin. Phys. B, 2024, 33 (1): 014205.   DOI: 10.1088/1674-1056/acd8ad Abstract （290）   HTML （1）    PDF （1176KB）（808）       Knowledge map    Finesse is a critical parameter for describing the characteristics of an optical enhancement cavity (OEC). This paper first presents a review of finesse measurement techniques, including a comparative analysis of the advantages, disadvantages, and potential limitations of several main methods from both theoretical and practical perspectives. A variant of the existing method called the free spectral range (FSR) modulation method is proposed and compared with three other finesse measurement methods, i.e., the fast-switching cavity ring-down (CRD) method, the rapidly swept-frequency (SF) CRD method, and the ringing effect method. A high-power OEC platform with a high finesse of approximately 16000 is built and measured with the four methods. The performance of these methods is compared, and the results show that the FSR modulation method and the fast-switching CRD method are more suitable and accurate than the other two methods for high-finesse OEC measurements. The CRD method and the ringing effect method can be implemented in open loop using simple equipment and are easy to perform. Additionally, recommendations for selecting finesse measurement methods under different conditions are proposed, which benefit the development of OEC and its applications.

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Variational quantum simulation of thermal statistical states on a superconducting quantum processer Xue-Yi Guo(郭学仪), Shang-Shu Li(李尚书), Xiao Xiao(效骁), Zhong-Cheng Xiang(相忠诚), Zi-Yong Ge(葛自勇), He-Kang Li(李贺康), Peng-Tao Song(宋鹏涛), Yi Peng(彭益), Zhan Wang(王战), Kai Xu(许凯), Pan Zhang(张潘), Lei Wang(王磊), Dong-Ning Zheng(郑东宁), and Heng Fan(范桁) Chin. Phys. B, 2023, 32 (1): 010307.   DOI: 10.1088/1674-1056/aca7f3 Abstract （827）   HTML （12）    PDF （3465KB）（785）       Knowledge map    Quantum computers promise to solve finite-temperature properties of quantum many-body systems, which is generally challenging for classical computers due to high computational complexities. Here, we report experimental preparations of Gibbs states and excited states of Heisenberg $XX$ and $XXZ$ models by using a 5-qubit programmable superconducting processor. In the experiments, we apply a hybrid quantum-classical algorithm to generate finite temperature states with classical probability models and variational quantum circuits. We reveal that the Hamiltonians can be fully diagonalized with optimized quantum circuits, which enable us to prepare excited states at arbitrary energy density. We demonstrate that the approach has a self-verifying feature and can estimate fundamental thermal observables with a small statistical error. Based on numerical results, we further show that the time complexity of our approach scales polynomially in the number of qubits, revealing its potential in solving large-scale problems.

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Reconstruction and functionalization of aerogels by controlling mesoscopic nucleation to greatly enhance macroscopic performance Chen-Lu Jiao(焦晨璐), Guang-Wei Shao(邵光伟), Yu-Yue Chen(陈宇岳), and Xiang-Yang Liu(刘向阳) Chin. Phys. B, 2023, 32 (3): 038103.   DOI: 10.1088/1674-1056/acb912 Abstract （843）   HTML （25）    PDF （7614KB）（712）       Knowledge map    This work presents a strategy for the mesoscopic engineering of hierarchically structured sodium alginate (SA) aerogels to enhance the macroscopic performance. The strategy was implemented by meso-functionalizing and reorganizing SA aerogels via controlled heterogeneous nucleation, in which microcrystalline cellulose-manganese dioxide (MCC-MnO2) nano-crystallites worked as template. Due to the short rod-like structure and abundant hydroxyl groups of MCC-MnO2, the organized mesostructure of SA aerogels was reconstructed during the assembly of SA molecule chains, which gave rise to a significant enhancement in macroscopic performance of SA areogels. For instance, the functionalized and reconstructed MCC-MnO2/SA aerogels acquired a more than 70% increase in mechanical strength with an excellent deformation recovery. Furthermore, an almost double enhancement of removal capacity for metal ions (i.e., Cu2+ and Pb2+) and organic dyes (i.e., congo red and methylene blue) was obtained for MnO2/SA aerogels, with an 87% repossession of the pollutants removal performance after 5 operation cycles.

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Intrinsic electronic structure and nodeless superconducting gap of YBa2Cu3O7-δ observed by spatially-resolved laser-based angle resolved photoemission spectroscopy Shuaishuai Li(李帅帅), Taimin Miao(苗泰民), Chaohui Yin(殷超辉), Yinghao Li(李颖昊), Hongtao Yan(闫宏涛), Yiwen Chen(陈逸雯), Bo Liang(梁波), Hao Chen(陈浩), Wenpei Zhu(朱文培), Shenjin Zhang(张申金), Zhimin Wang(王志敏), Fengfeng Zhang(张丰丰), Feng Yang(杨峰), Qinjun Peng(彭钦军), Chengtian Lin(林成天), Hanqing Mao(毛寒青), Guodong Liu(刘国东), Zuyan Xu(许祖彦), Lin Zhao(赵林), and X J Zhou(周兴江) Chin. Phys. B, 2023, 32 (11): 117401.   DOI: 10.1088/1674-1056/acf498 Abstract （408）   HTML （10）    PDF （6820KB）（712）       Knowledge map    The spatially-resolved laser-based high-resolution angle resolved photoemission spectroscopy (ARPES) measurements have been performed on the optimally-doped YBa2Cu3O7-δ (Y123) superconductor. For the first time, we found the region from the cleaved surface that reveals clear bulk electronic properties. The intrinsic Fermi surface and band structures of Y123 were observed. The Fermi surface-dependent and momentum-dependent superconducting gap was determined which is nodeless and consistent with the d+is gap form.

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Experimental realization of two-dimensional single-layer ultracold gases of 87Rb in an accordion lattice Liangwei Wang(王良伟), Kai Wen(文凯), Fangde Liu(刘方德), Yunda Li(李云达), Pengjun Wang(王鹏军), Lianghui Huang(黄良辉), Liangchao Chen(陈良超), Wei Han(韩伟), Zengming Meng(孟增明), and Jing Zhang(张靖) Chin. Phys. B, 2022, 31 (10): 103401.   DOI: 10.1088/1674-1056/ac873c Abstract （1184）   HTML （25）    PDF （1293KB）（710）       Knowledge map    We experimentally realize two-dimensional (2D) single-layer ultracold gases of 87Rb by dynamically tuning the periodicity of a standing wave, known as accordion lattice. In order to load 87Rb Bose—Einstein condensate into single dark fringe node of the blue detuning optical lattice, we reduce the lattice periodicity from 26.7 μ to 3.5 μ with the help of an acousto-optic deflector (AOD) to compress the three-dimensional BEC adiabatically into a flat and uniform quasi-2D single-layer. We describe the experimental procedure of the atoms loading into the accordion lattice in detail and present the characteristics of the quasi-2D ultracold gases. This setup provides an important platform for studying in- and out-of equilibrium physics, phase transition and 2D topological matter.

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Atomic optical spatial mode extractor for vector beams based on polarization-dependent absorption Hong Chang(常虹), Xin Yang(杨欣), Jinwen Wang(王金文), Yan Ma(马燕), Xinqi Yang(杨鑫琪), Mingtao Cao(曹明涛), Xiaofei Zhang(张晓斐), Hong Gao(高宏), Ruifang Dong(董瑞芳), and Shougang Zhang(张首刚) Chin. Phys. B, 2023, 32 (3): 034207.   DOI: 10.1088/1674-1056/acac19 Abstract （611）   HTML （8）    PDF （8912KB）（686）       Knowledge map    Vector beams with spiral phase and spatially varying polarization profiles have many applications from optical micromanipulation to materials processing. Here, we propose and demonstrate an atomic spatial mode extracting scheme for the vector beam based on polarization-dependent absorption in the atom vapor. By employing the linear polarization pump beam which induces polarization sensitive absorption in the atomic ensemble, a counter-propagated weak probe vector beam is extracted by spatial absorption, and extracted part still maintains the original polarization and the vortex phase. The topological charges of the extracted mode are verified by interfering with the Gaussian beam, and it can be found that the orbital angular momentum is conserved in the extracting process. Our work will have potential applications in non-destructive spatial mode identification, and is also useful for studying higher-dimensional quantum information based on atomic ensembles.

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Image segmentation of exfoliated two-dimensional materials by generative adversarial network-based data augmentation Xiaoyu Cheng(程晓昱), Chenxue Xie(解晨雪), Yulun Liu(刘宇伦), Ruixue Bai(白瑞雪), Nanhai Xiao(肖南海), Yanbo Ren(任琰博), Xilin Zhang(张喜林), Hui Ma(马惠), and Chongyun Jiang(蒋崇云) Chin. Phys. B, 2024, 33 (3): 030703.   DOI: 10.1088/1674-1056/ad23d8 Abstract （645）   HTML （43）    PDF （1065KB）（682）       Knowledge map    Mechanically cleaved two-dimensional materials are random in size and thickness. Recognizing atomically thin flakes by human experts is inefficient and unsuitable for scalable production. Deep learning algorithms have been adopted as an alternative, nevertheless a major challenge is a lack of sufficient actual training images. Here we report the generation of synthetic two-dimensional materials images using StyleGAN3 to complement the dataset. DeepLabv3Plus network is trained with the synthetic images which reduces overfitting and improves recognition accuracy to over 90%. A semi-supervisory technique for labeling images is introduced to reduce manual efforts. The sharper edges recognized by this method facilitate material stacking with precise edge alignment, which benefits exploring novel properties of layered-material devices that crucially depend on the interlayer twist-angle. This feasible and efficient method allows for the rapid and high-quality manufacturing of atomically thin materials and devices.

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Orientation determination of nitrogen-vacancy center in diamond using a static magnetic field Yangpeng Wang(王杨鹏), Rujian Zhang(章如健), Yan Yang(杨燕), Qin Wu(吴琴), Zhifei Yu(于志飞), and Bing Chen(陈冰) Chin. Phys. B, 2023, 32 (7): 070301.   DOI: 10.1088/1674-1056/acc0f7 Abstract （311）   HTML （6）    PDF （1149KB）（677）       Knowledge map    Nitrogen-vacancy (NV) centers in a bulk diamond are often employed to realize measurement of multiple physical quantities, which depends on orientation information of NV axis. We report a fast and effective method to determine the orientation of NV axis with the aid of a static magnetic field. By measuring the optically detected magnetic resonance spectra, we can precisely extract the polar angle information between the NV axis and the known magnetic field. Combining with the polar angle information of different kinds of NV centers, we employ the Nelder-Mead algorithm to get the optimal solution of the orientation of NV axis. This method is simple and efficient, and is easily applied in NV-based quantum sensing.

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Bismuth doping enhanced tunability of strain-controlled magnetic anisotropy in epitaxial Y3Fe5O12(111) films Yunpeng Jia(贾云鹏), Zhengguo Liang(梁正国), Haolin Pan(潘昊霖), Qing Wang(王庆), Qiming Lv(吕崎鸣), Yifei Yan(严轶非), Feng Jin(金锋), Dazhi Hou(侯达之), Lingfei Wang(王凌飞), and Wenbin Wu(吴文彬) Chin. Phys. B, 2023, 32 (2): 027501.   DOI: 10.1088/1674-1056/ac67cc Abstract （928）   HTML （8）    PDF （893KB）（671）       Knowledge map    Y3Fe5O12 (YIG) and BiY2Fe5O12 (Bi:YIG) films were epitaxially grown on a series of (111)-oriented garnet substrates using pulsed laser deposition. Structural and ferromagnetic resonance characterizations demonstrated the high epitaxial quality, extremely low magnetic loss and coherent strain state in these films. Using these epitaxial films as model systems, we systematically investigated the evolution of magnetic anisotropy (MA) with epitaxial strain and chemical doping. For both the YIG and Bi:YIG films, the compressive strain tends to align the magnetic moment in the film plane while the tensile strain can compete with the demagnetization effect and stabilize perpendicular MA. We found that the strain-induced lattice elongation/compression along the out-of-plane [111] axis is the key parameter that determines the MA. More importantly, the strain-induced tunability of MA can be enhanced significantly by Bi doping; meanwhile, the ultralow damping feature persists. We clarified that the cooperation between strain and chemical doping could realize an effective control of MA in garnet-type ferrites, which is essential for spintronic applications.

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Room-temperature creation and manipulation of skyrmions in MgO/FeNiB/Mo multilayers Wen-Hui Liang(梁文会), Jian Su(苏鉴), Yu-Tong Wang(王雨桐), Ying Zhang(张颖), Feng-Xia Hu(胡凤霞), and Jian-Wang Cai(蔡建旺) Chin. Phys. B, 2023, 32 (12): 127504.   DOI: 10.1088/1674-1056/acf5d4 Abstract （553）   HTML （0）    PDF （6693KB）（666）       Knowledge map    Magnetic skyrmions in multilayer structures are considered as a new direction for the next generation of storage due to their small size, strong anti-interference ability, high current-driven mobility, and compatibility with existing spintronic technology. In this work, we present a tunable room temperature skyrmion platform based on multilayer stacks of MgO/FeNiB/Mo. We systematically studied the creation of magnetic skyrmions in MgO/FeNiB/Mo multilayer structures with perpendicular magnetic anisotropy (PMA). In these structures, the magnetic anisotropy changes from PMA to in-plane magnetic anisotropy (IMA) as the thickness of FeNiB layer increases. By adjusting the applied magnetic field and electric current, stable and high-density skyrmions can be obtained in the material system. The discovery of this material broadens the exploration of new materials for skyrmion and promotes the development of spintronic devices based on skyrmions.

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Recent progress on valley polarization and valley-polarized topological states in two-dimensional materials Fei Wang(王斐), Yaling Zhang(张亚玲), Wenjia Yang(杨文佳), Huisheng Zhang(张会生), and Xiaohong Xu(许小红) Chin. Phys. B, 2024, 33 (1): 017306.   DOI: 10.1088/1674-1056/ad0713 Abstract （310）   HTML （29）    PDF （1820KB）（662）       Knowledge map    Valleytronics, using valley degree of freedom to encode, process, and store information, may find practical applications in low-power-consumption devices. Recent theoretical and experimental studies have demonstrated that two-dimensional (2D) honeycomb lattice systems with inversion symmetry breaking, such as transition-metal dichalcogenides (TMDs), are ideal candidates for realizing valley polarization. In addition to the optical field, lifting the valley degeneracy of TMDs by introducing magnetism is an efficient way to manipulate the valley degree of freedom. In this paper, we first review the recent progress on valley polarization in various TMD-based systems, including magnetically doped TMDs, intrinsic TMDs with both inversion and time-reversal symmetry broken, and magnetic TMD heterostructures. When topologically nontrivial bands are empowered into valley-polarized systems, valley-polarized topological states, namely valley-polarized quantum anomalous Hall effect can be realized. Therefore, we have also reviewed the theoretical proposals for realizing valley-polarized topological states in 2D honeycomb lattices. Our paper can help readers quickly grasp the latest research developments in this field.