Based on our recently published work [Front. Phys. 21, 093201 (2026)], we extend the analysis to the density-operator evolution of a two-mode entangled quantum system subject to amplitude decay and show that the output state retains the same functional structure as the initial density operator throughout the decay. We further examine the evolutions of several quantum statistical distributions and the von Neumann entropy used to quantify entanglement during the process. This work offers a systematic approach to studying two-mode entangled open systems and yields results on the von Neumann entropy that may help facilitate entanglement measurement.

Quantum secure direct communication (QSDC) enables the direct transmission of confidential information without pre-shared keys. However, device imperfections in practical systems can lead to information leakage. The Trojan-horse attack (THA), a stealthy side-channel threat, steals information by injecting photons into encoding devices and analyzing the reflected light. This paper focuses on the single-photon-based (DL04) protocol, establishing for the first time a comprehensive THA model against it. By combining weak coherent pulse (WCP) sources with the decoy-state method, we systematically analyze the security under THA during both the first and second rounds of transmission, derive analytical expressions for the secrecy message capacity, and quantitatively evaluate the impact of attack strength on system performance through numerical simulations. Our results demonstrate that the system’s security is highly sensitive to the average number of reflected Trojan photons, {\mu }_{\mathrm{o}\mathrm{u}\mathrm{t}}. For a first-round attack, the secrecy message capacity remains nearly identical to the attack-free case when {\mu }_{\mathrm{o}\mathrm{u}\mathrm{t}}\le {10}^{-8}, but drops to zero when {\mu }_{\mathrm{o}\mathrm{u}\mathrm{t}} increases to {10}^{-3}. In contrast, the second round of attacks had a weaker impact. Even at the strongest attack intensity ({\mu }_{\mathrm{o}\mathrm{u}\mathrm{t}}={10}^{-2}), the system could still maintain a certain level of secrecy message capacity. When THA simultaneously targets both the first and second rounds, the overall security of the system is predominantly governed by the more sensitive first-round attack, whose security boundary remains largely comparable to that observed in a single first-round attack scenario. Furthermore, We perform parameter optimization to achieve the optimal secrecy message capacity for each channel attenuation. Our study provides the first quantitative security bound for THA on DL04 protocol, offering practical guidance for encoder isolation requirements in future implementations.

Nonlayered two-dimensional (2D) β-In₂S₃ nanostructures have demonstrated outstanding electronic and optoelectronic properties, which requires its large-scale single-crystalline films to suppress carrier scattering. However, the weak energy for In−S chemical bonds and inherent nonlayered structure with three dimensional bonds make it highly challenging to achieve large area 2D β-In₂S₃ nanoflakes, which is still limited by the high nucleation density and three-dimensional isotropic growth tendency. Herein, we propose a universal strategy of suppressing nucleation and slow-kinetic epitaxial growth of large domain 2D nonlayered β-In₂S₃ nanoflakes via water molecules for the optoelectronic applications. The water molecules acted as the function of partially oxidized In₂S₃ nucleus via mild oxidation, which reduced the nucleation density by approximately three orders of magnitude and enabled the formation of large-area single-crystal with an average domain size of 120 μm and a maximum size approaching 270 μm. The structural characteristics and electronic structures of our β-In₂S₃ samples characterized by various characterization techniques showed unique single-crystalline nature and modified Fermi level properties. Furthermore, the diverse nanostructures of β-In₂S₃ could be precisely tuned from triangular nanosheets to nanowires by controlling the growth conditions. The two-terminal β-In₂S₃ photodetectors exhibited excellent performance with a high photoresponsivity of 44 A·W⁻¹ and a fast response speed with rise and decay times of 6 and 7 ms, respectively, revealing the superior physical properties of large domain 2D β-In₂S₃. This work provides a universal water-assisted strategy for synthesizing large-area 2D non-layered materials and paves the way for significant potential of high-quality large-scale single-crystalline β-In₂S₃ for advanced optoelectronic devices applications.

In nanoscale metal-oxide-semiconductor field-effect transistors (MOSFETs), excess noise has been experimentally observed as the channel length is scaled down. Theoretical analyses indicate that as the channel length decreases, the dominant component of excess noise gradually changes from modified thermal noise to suppressed shot noise. However, no clear quantitative analysis has been provided regarding the specific conditions for this transition. In this paper, based on a device current model, we analyze the transition conditions under which shot noise replaces thermal noise as the dominant component of excess noise. In the modeling process, we comprehensively consider short-channel effects, including the electric field distribution, mobility reduction caused by electron temperature gradients, and the hot-carrier effect. Meanwhile, we use 3D Monte Carlo simulations to analyze the channel current noise components in MOSFETs with different channel lengths, and we simulate the effects of drain–source voltage, gate voltage, temperature, and substrate doping density on the transition of excess noise components. The simulation results show that the transition trend of excess noise components is consistent with predictions from the physical model: the critical channel length for the transition from thermal noise to shot noise in nanoscale MOSFETs is approximately 20 nm. The model and simulation results presented in this paper agree with reported experimental measurements and provide a theoretical foundation for the quantitative analysis of excess noise components in nanoscale MOSFETs.

Space-time modulation provides a powerful approach for controlling wave behavior and enables forms of wave manipulation that are unattainable in stationary systems. Here, we propose a generalized transfer matrix method for analyzing wave propagation in periodic space-time modulated systems. The proposed method relaxes the commonly assumed sinusoidal modulation constraint and accommodates an arbitrary number of time-varying components with general periodic modulations. A two-membrane acoustic system subjected to three representative periodic modulations — namely, square-wave modulation, triangular-wave modulation, and sawtooth-wave modulation — is investigated. The results demonstrate that the proposed method enables accurate and efficient analysis of weakly modulated space-time periodic systems. This framework provides a versatile tool for analyzing complex space-time modulated structures and may facilitate the development of advanced acoustic devices for applications such as underwater communication, medical ultrasound, and noise control.

We investigated the gate-tunable spin transistor structured as a ferromagnet–topological insulator–ferromagnet junction implemented on a zigzag phosphorene nanoribbon. By applying a gate voltage to the device region, the wave vector of the channel can be effectively modulated, thereby shifting the resonance condition of the junction and enabling efficient tuning of the spin-dependent conductance. The conductance of the junction can be switched between e^2/h and 0, corresponding to the ON and OFF states, respectively. Our work demonstrates a feasible strategy for realizing spin transistors and highlights the potential of such systems for future spintronic applications.

Two-dimensional (2D) materials that exhibit magnetism and piezoelectricity offer exciting opportunities for next-generation spintronic and multifunctional devices. The recently synthesized 2D hexagonal Fe₂O₃ provides a promising platform [Nat. Mater. 20, 1073 (2021)], yet its atomic structure remains unidentified. Herein, we report that high-throughput first-principles screening reveals a viable monolayer structure that can serve as a candidate for experimental realization. The proposed hexagonal Fe₂O₃ monolayer features a large direct band gap of 3.1 eV and hosts a robust chiral antiferromagnetic order stabilized by the interplay between triangular-lattice-induced geometric frustration and strong magnetic anisotropy. The absence of inversion symmetries gives rise to a pronounced in-plane piezoelectric response, with a d₁₁ coefficient of −29.51 pm/V. Remarkably, these key electronic, magnetic, and piezoelectric properties remain robust under biaxial strain, highlighting the hexagonal Fe₂O₃ monolayer as a multifunctional candidate for piezoelectrically engineered spintronic applications.

The bulk photovoltaic effect (BPVE) is mostly studied in ferroelectric and piezoelectric systems with a sizable intrinsic and induced electric dipole moment. While most studies of BPVE are based on the conventional positive piezoelectric materials, their responses in negative piezoelectric systems remain rare. In this work, based on a minimum tight-binding model simulation, we adopt a chain model to illustrate how the BPVE evolves under mechanical deformation in negative piezoelectrics. We find that the BPVE responses are mainly governed by strain-induced shift vector variations. This is in contrast to the conventional positive piezoelectrics. Moreover, such a mechanism is further illustrated in realistic quasi-layered negative piezoelectrics, i.e., rhombohedral GeX (X = S, Se, Te), via density functional theory calculations. Our work provides in-depth insights into BPVE engineering in unconventional negative piezoelectrics.

Driving non-superconducting materials into a superconducting state through specific modulation is a key focus in the field of superconductivity. Pressure is a powerful method that can switch a three-dimensional (3D) material between non-superconducting and superconducting states. In the two-dimensional (2D) case, strain engineering plays a similar role to pressure. However, purely strain-induced superconductivity in 2D systems remains exceedingly scarce. Using first-principles calculations, we demonstrate that a superconducting transition can be induced solely by applying biaxial tensile strain in a 2D carbon allotrope, THO-graphene, which is composed of triangles, hexagons, and octagons. Free-standing THO-graphene is non-superconducting. Surprisingly, the electron-phonon coupling in strained THO-graphene is enhanced strong enough to pair electrons and realize superconductivity, with the highest superconducting transition temperature reaching 45 K. This work not only provides a notable example of controlling metal-superconductor transition in 2D system just via strain, but also sets a new record of superconducting transition temperature for 2D elemental superconductors. We propose a template-assisted epitaxial growth strategy to obtain THO-graphene, with 2H-MoTe₂ as substrate.

We investigate a one-dimensional system featuring simultaneous off-diagonal and diagonal quasiperiodic modulations. By analyzing the fractal dimension, we map out the delocalization−localization phase diagram. We demonstrate that delocalized and localized states can be distinguished via the Wigner distribution, while extended, critical, and localized phases are separated using the Wigner entropy. Furthermore, we explore the quantum thermodynamic properties, revealing that localized states facilitate the emergence of a quantum heater mode, alongside the appearance of a refrigerator mode. In addition, the efficiency of the quantum engine and the coefficient of performance of the quantum refrigerator are analyzed and discussed. These findings enhance our understanding of localization phenomena and expand the thermodynamic applications of quasiperiodic systems.

Iron antimonide (FeSb₂) is a prototypical correlated narrow-gap system that exhibits a metal−insulator-like crossover and a concomitant diamagnetic-to-paramagnetic transition. However, the microscopic physical origin of these anomalous electrical and magnetic behaviors has been the subject of a long-standing debate. Two competing physical pictures have been proposed: the Kondo insulator (KI) framework, which attributes the gap formation to Kondo hybridization, and the spin-state excitation (SSE) mechanism, which emphasizes a thermally activated transition from a low-spin state to a high-spin state. In this review, we provide a critical overview of key experimental results from electrical transport, magnetic properties, and a broad range of spectroscopic probes, assessing how each supports or challenges these competing physical pictures. Particular attention is paid to recent advances in element- and orbital-sensitive spectroscopies, such as X-ray absorption spectroscopy (XAS), which together offer direct insights into the evolution of the Fe spin state and electronic structure. Additional anomalous properties, such as the colossal thermoelectric effect and spin-structure instabilities, are also discussed in the end. These emerging features not only underscore the complexity of this correlated narrow-gap system but also suggest rich, unresolved physics beyond existing models, inviting further investigation into its fundamental behavior and potential applications.