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    20 October 2026, Volume 46 Issue 5 Previous Issue   

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    Development of high purity and high heralding efficiencysingle-photon source based on PPKTP crystal
    YANG Tingyu, LI Fengpei, CHEN Jianlan, ZHANG Han
    2026, 46 (5):  217-224.  doi: 10.13725/j.cnki.pip.2026.05.001
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    Single-photon sources are crucial for fields such as optical quantum informa-tion processing and secure communication. Current heralded single-photon sources based onspontaneous parametric down-conversion in nonlinear crystals often struggle to simultaneouslyachieve high heralding efficiency and high purity, which directly limits the secure key rateand transmission distance of quantum key distribution. In this paper, we develop a high-purity, high-heralding-efficiency single-photon source based on a PPKTP nonlinear crystal using continuous-wave pumped spontaneous parametric down-conversion. By employing a longcrystal and optimizing the pump beam waist, the photon heralding efficiency and collectionefficiency are significantly improved. Under an experimental condition with a pump powerof 1 mW, source brightness of 6.3 x 104 pairs/(s-mW) and heralding efficiency of 57.3%, asingle-photon purity of 0.994 6 is achieved. Additionally, the source exhibits good stability andstrong suppression of multiphoton noise. The results provide a feasible solution for fabricatinglow-cost, high-quality heralded single-photon sources.

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    Advances in excited-state dynamics of perovskite nanocrystals
    WU Xiaowei, QIAN Haining , ZHANG Chunfeng
    2026, 46 (5):  225-245.  doi: 10.13725/j.cnki.pip.2026.05.002
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    Perovskite semiconductor nanocrystals have demonstrated tremendous potential in lasers, light-emitting diodes, and quantum light sources due to their outstanding light-emitting properties. The performance of these devices is closely tied to the excitedstate dynamics of their constituent nanocrystals. This review systematically summarizes the
    excited states and the associated multiscale dynamics in perovskite semiconductor nanocrystals, including the generation, relaxation, and recombination dynamics of photo-excited carriers; the fine structure and coherent dynamics of band-edge excitons; the spin dynamics; and the coherent control of energy levels under strong optical fields. In addition, the key scientific questions and technical challenges in this field are discussed.

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    Application of the surface Green’s function method in first-principles quantum transport simulations#br#
    CHEN Yifan , LÜ Jin , LI Hong
    2026, 46 (5):  246-254.  doi: 10.13725/j.cnki.pip.2026.05.003
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    The surface Green’s function (SGF) method provides an advanced solution for overcoming the intrinsic limitations of conventional slab models in first-principles quantum transport simulations. Traditional slab models suffer from finite-size effects, spurious coupling between two surfaces, and Fermi-level shifts, leading to slow convergence and distorted results in calculations of work functions, surface states, and electrochemical interfaces. The SGF approach partitions a semi-infinite system into a finite surface region and a semiinfinite bulk region, where the latter acts as an infinite electron reservoir coupled to the surface through a self-energy term, enabling self-consistent calculations under open boundary conditions. Implemented within density functional theory and linear combination of atomic orbitals (LCAO) basis sets, the method evaluates the Green’s function via complex contour integration and efficient recursive algorithms, achieving a computational cost that scales linearly with the number of atomic layers and a band convergence behavior far superior to that of slab models. This review systematically surveys the application of the SGF method in representative scenarios including metal work function calculations, band alignment of semiconductor
    heterojunctions, accurate description of surface states, and modulation of surface chemistry under external electrostatic fields. The results demonstrate the combined advantages of SGF in accuracy, efficiency, and physical soundness, establishing it as a powerful tool for advanced quantum simulations of surfaces and interfaces.
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    Applications and exploration of information theory in biological#br# systems#br#
    ZHAO Peiyi , ZHOU Bangyan , WU Renjie
    2026, 46 (5):  255-270.  doi: 10.13725/j.cnki.pip.2026.05.004
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    Biological systems utilize multi-layered information transmission networks to sense and adapt to their internal and external environments. The inherent nonlinearity, stochasticity, and multi-scale coupling characteristics of these systems pose great challenges to traditional analytical methods. Information theory, as a powerful theoretical framework for quantifying system uncertainty and correlations, employs core metrics such as entropy, mutual
    information, and channel capacity to overcome the limitations of conventional analyses, providing a novel perspective on the flow of information in biological systems. This paper systematically reviews the applications of information theory in network regulation and signal transmission research, detailing its fundamental principles, computational methods, and key application scenarios. We emphasize the unique advantages of mutual information in addressing
    biological noise, revealing nonlinear regulatory relationships, and integrating multi-omics data while analyzing current challenges and future directions for development.

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