Chinese Physics B

Qi, Wei; Guo, Xiao-Gang; Dong, Liang-Wei; Zhang, Xiao-Fei

doi: 10.1088/1674-1056/ac891apmid: N/A

We study modulational instability of a resonantly polariton condensate in a discrete lattice. Employing a discrete gain-saturation model, we derive the dispersion relation for the modulational instability by means of the linear-stability analysis. Effects of the pumping strength, the nonlinearity, the strength of the detuning, and the coupling strength on the modulation instability are investigated. It is found that the interplay between these parameters will dramatically change the modulational instability condition. We believe that the predicted results in this work can be useful for future possible experiment of exciton-polariton condensate in lattices.

Ma, Xiaoguang; Hu, Fangzhen; Chen, Xi; Wang, Yimeng; Hao, Xiaojian; Gu, Min; Zhang, Qiming

doi: 10.1088/1674-1056/acaf2apmid: N/A

Nonlinear materials have gained wide interest as saturable absorbers and pulse compression for pulsed laser applications due to their unique optical properties. This work investigates the third-order nonlinear phenomenon of tungsten trioxide (WO3) thin films. The giant nonlinear absorption and nonlinear refractive index of WO3 thin films were characterized by Z-scan method at 800 nm. We experimentally observed the giant saturable absorption (SA) and nonlinear refractive index of WO3 thin films prepared by the seedless layer hydrothermal method, with SA coefficient being as high as –2.59 × 105 cm⋅GW−1. The SA coefficient is at least one order of magnitude larger than those of the conventional semiconductors. The nonlinear refractive index n2 of WO3 film has been observed for the first time in recent studies and the corresponding coefficient can be up to 1.793 cm2⋅GW−1. The large third-order nonlinear optical (NLO) response enables WO3 thin films to be promising candidates for optoelectronic and photonic applications in the near-infrared domain.

Li, Zonglin; Tian, Qiang; Hu, Haiyan

doi: 10.1088/1674-1056/aca5ffpmid: N/A

This paper presents an experimental study on the resistance law of a rod vertically penetrating different kinds of multilayer granular rafts with a constant velocity so as to reveal the mechanical properties of the multilayer granular rafts. The resistance was quasi-static under the chosen velocity. Experiments were conducted with different granular thicknesses, rod diameters and combinations of particles and liquids. The study shows that the resistance–displacement relation of the rod has three smooth stages. In the first stage, the resistance rapidly increased. In the second stage, the resistance curve maintained an almost constant slope. In the third stage, the resistance smoothly changed with its slope continuously increasing. Based on the corresponding physical models for each stage, the study reveals the exponential dependence of the load-bearing capacity of the multilayer granular raft on its thickness, and clarifies the capillary effects on the resistance law. The study extends the knowledge of the granular raft from monolayer to multilayer structure.

Feng, Bao; Huang, Hai-Dong; Bian, Yu-Xiang; Jia, Wei; Zhou, Xing-Yu; Wang, Qin

doi: 10.1088/1674-1056/ac9b33pmid: N/A

Quantum key distribution (QKD) in principle can provide unconditional secure communication between distant parts. However, when finite-key length is taken into account, the security can only be ensured within certain security level. In this paper, we adopt the Chernoff bound analysis method to deal with finite-key-size effects, carrying out corresponding investigations on the relationship between the key generation rate and security parameters for different protocols, including BB84, measurement-device-independent and twin-field QKD protocols. Simulation results show that there exists a fundamental limit between the key rate and the security parameters. Therefore, this study can provide valuable references for practical application of QKD, getting a nice balance between the key generation rate and the security level.

Jiang, Xin; Li, Chen-Hao; Yang, Shuo-Xiong; Liang, Jia-Hao; Lai, Long-Kun; Dong, Qing-Yang; Huang, Wei; Liu, Xin-Yu; Luo, Wei-Jun

doi: 10.1088/1674-1056/ac8735pmid: N/A

The reverse gate leakage mechanism of W-gate and TiN-gate AlGaN/GaN high-electron-mobility transistors (HEMTs) with N2 plasma surface treatment is investigated using current–voltage (I–V) and capacitance–voltage (C–V) characteristics and theoretical calculation analysis. It is found that the main reverse gate leakage mechanism of both devices is the trap-assisted tunneling (TAT) mechanism in the entire reverse bias region (–30 V to 0 V). It is also found that the reverse gate leakage current of the W-gate AlGaN/GaN HEMTs is smaller than that of the TiN gate at high reverse gate bias voltage. Moreover, the activation energies of the extracted W-gate and TiN-gate AlGaN/GaN HEMTs are 0.0551 eV–0.127 eV and 0.112 eV–0.201 eV, respectively.

Tang, Yi-Fan; Lin, Shu-Yu

doi: 10.1088/1674-1056/ac9fc0pmid: N/A

Source illusion is an important issue in acoustic fields that has significant applications in various practical scenarios. Recent progress in acoustic metasurfaces has broken the limitation of manipulating large-scale waves at subwavelength scales and enables a better illusion capability, while there is still a problem that most previous studies are hampered by a lack of tuning capability. Here we propose a reconfigurable source illusion device capable of providing azimuthally-dependent phase delay in real-time via changing the static voltage distribution. The resulting device is implemented by employing an adjustable piezoelectric metasurface with a subwavelength thickness that can achieve a full 2π-phase shift while maintaining efficient transmittance. The effectiveness of our mechanism is demonstrated via two distinctive source illusion phenomena of shifting and transforming a simple point source without changing the device geometry. We anticipate that our methodology, which does not require a large device size or a complicated phased array, will open up new avenues for the miniaturization and integration of source illusion devices and may promote their on-chip applications in a variety of fields, such as acoustic camouflage and manipulation precision.

Wang, Ying; Qi, Feng; Zhang, Zi-Xu; Wang, Jin-Kuan

doi: 10.1088/1674-1056/aca9c7pmid: N/A

Terahertz (THz) imaging has drawn significant attention because THz wave has a unique capability to transient, ultra-wide spectrum and low photon energy. However, the low resolution has always been a problem due to its long wavelength, limiting their application of fields practical use. In this paper, we proposed a complex one-shot super-resolution (COSSR) framework based on a complex convolution neural network to restore superior THz images at 0.35 times wavelength by extracting features directly from a reference measured sample and groundtruth without the measured PSF. Compared with real convolution neural network-based approaches and complex zero-shot super-resolution (CZSSR), COSSR delivers at least 6.67, 0.003, and 6.96% superior higher imaging efficacy in terms of peak signal to noise ratio (PSNR), mean square error (MSE), and structural similarity index measure (SSIM), respectively, for the analyzed data. Additionally, the proposed method is experimentally demonstrated to have a good generalization and to perform well on measured data. The COSSR provides a new pathway for THz imaging super-resolution (SR) reconstruction below the diffraction limit.

Zeng, Jing; Song, Yaju; Lu, Jing; Zhou, Lan

doi: 10.1088/1674-1056/acac18pmid: N/A

We investigate the non-Markovianity (NM) of a waveguide QED with a two-level atom as the system and a semi-infinite rectangular waveguide as the environment, where the transverse magnetic (TMmn) modes define the quantum channels of guided photons. The perfect mirror imposed by the finite end exerts a retarded feedback mechanism to allow for information backflow, which leads to NM dynamics. For the energy separation of the atom far away from the cutoff frequencies of transverse modes, the delay differential equations are obtained with single-excitation initial in the atom. Our attention is focused on the effects of multiple quantum channels involved in guiding photons on the degree of non-Markovian behavior. An asymptotic value of the non-Markovianity N1can be found as the atom–mirror distance is large enough, however, the asymptotic value of N2of the atom interacting with the effective double-modes is lower than that of the atom interacting with the effective single-mode. We also show that N1is a constant, and the analytical expression for N2is related to the parameters associated with the modes, which is related to the interference of the two modes.

Zhang, Xiaoya; Cheng, Yingjie; Zhao, Chunyu; Gao, Jingwan; Kan, Dongxiao; Wang, Yizhan; Qi, Duo; Wei, Yingjin

doi: 10.1088/1674-1056/aca6dapmid: N/A

Fe/Co-based diatomic catalysts decorated on an N-doped graphene substrate are investigated by first-principles calculations to improve the electrochemical properties of Li–S batteries. Our results demonstrate that FeCoN8@Gra not only possesses moderate adsorption energies towards Li2Snspecies, but also exhibits superior catalytic activity for both reduction and oxidation reactions of the sulfur cathode. Moreover, the metallic property of the diatomic catalysts can be well maintained after Li2Snadsorption, which could help the sulfur cathode to maintain high conductivity during the whole charge–discharge process. Given these exceptional properties, it is expected that FeCoN8@Gra could be a promising diatomic catalyst for Li–S batteries and afford insights for further development of advanced Li–S batteries.

Du, Ming-Jing; Sun, Bao-Jun; Kai, Ge

doi: 10.1088/1674-1056/ac9368pmid: N/A

This paper is aimed at solving the nonlinear time-fractional partial differential equation with two small parameters arising from option pricing model in financial economics. The traditional reproducing kernel (RK) method which deals with this problem is very troublesome. This paper proposes a new method by adaptive multi-step piecewise interpolation reproducing kernel (AMPIRK) method for the first time. This method has three obvious advantages which are as follows. Firstly, the piecewise number is reduced. Secondly, the calculation accuracy is improved. Finally, the waste time caused by too many fragments is avoided. Then four numerical examples show that this new method has a higher precision and it is a more timesaving numerical method than the others. The research in this paper provides a powerful mathematical tool for solving time-fractional option pricing model which will play an important role in financial economics.