High-dimensional quantum key distribution (QKD) based on entangled qudits has emerged as a promising route for advancing the performance and practicality of quantum communication. By extending beyond the qubit framework, qudit entanglement enables the encoding of multiple bits per particle and offers greater robustness against noise, loss, and eavesdropping. In this review, we present qudit-based entanglement QKD protocols and their experimental demonstrations. We first introduce the basic concepts of qudits and provide an overview of foundational qubit-based entanglement QKD schemes, such as Ekert '91 (E91) and Bennett–Brassard–Mermin '92 (BBM92), which establish the core principles of entanglement-based secure key generation. Subsequently, we examine the generalization of these protocols to entangled qudits, highlighting how higher dimensionality enhances secure key rates and noise tolerance. Finally, we survey experimental demonstrations of qudit-based entanglement QKD across photonic platforms and outline prospects, showing that high-dimensional entanglement can be reliably generated, distributed, and measured for QKD with high stability and scalability. Remarkably, these achievements not only verify the feasibility of practical high-dimensional QKD, but also demonstrate clear advantages over qubit-based systems. Overall, theoretical frameworks and experimental realizations reviewed here position photonic qudit-based entanglement QKD as a promising resource for scalable, high-speed, and secure quantum communication networks, unveiling its potential as a central component in the future of quantum information technologies.
Light-sheet fluorescence microscopy (LSFM) has emerged as a powerful optical imaging technique for studying complex biological systems, particularly in neuroscience. By selectively illuminating a thin optical plane and combining it with camera-based widefield detection, LSFM enables rapid volumetric imaging with reduced photobleaching and phototoxicity compared to point-scanning approaches, such as confocal and multiphoton microscopy. Originally developed for imaging small, transparent organisms, LSFM has evolved into a versatile platform capable of probing large specimens, including whole mouse brains and human tissue samples, through the integration of advanced optical clearing techniques and sophisticated data-analysis tools. This review is focused on the optical principles underlying LSFM, the recent technological developments in light-sheet generation and system configurations, and their impact on imaging performances in highly-scattering tissues. It also discusses practical considerations related to the multiple optical clearing methodologies developed in recent decades and highlights representative applications in brain structural mapping. Finally, it outlines current challenges in data handling and imaging artifacts, and briefly considers future directions for integrating LSFM with complementary imaging modalities.
Materials that exhibit reversible field-tunable responses to electric and magnetic stimuli enable adaptive modulation of mechanical, dielectric, and magnetic properties. This review focuses on electro-magnetorheological (EMR) hybrid materials that concurrently exploit electric polarization and magnetization-induced structure formation, with particular emphasis on protocol-dependent, non-additive behavior under superimposed fields. The underlying electrorheological (ER) and magnetorheological (MR) response mechanisms are analyzed from classical dipolar models to advanced descriptions that incorporate interfacial polarization phenomena, effective (microstructure-mediated) magnetoelectric coupling, and nonlinear structural dynamics. Microscopic interaction mechanisms are consistently linked to the macroscopic rheological and functional behavior of EMR fluids, gels, and elastomers, with an emphasis on viscoelastic properties, electrical conductivity, and cross-field coupling effects. The impact of field orientation, application sequence, and driving frequency on emergent material behavior is critically evaluated. The design and synthesis concepts for bifunctional particles and hierarchical composites are summarized. Key challenges related to colloidal and structural stability, response reproducibility, scalable manufacturing routes, and environmental sustainability are also discussed. Emerging multiscale and data-driven modeling frameworks are highlighted as enabling tools for predictive material design and optimization of EMR materials. Standardization needs in measurement protocols and reporting practices are addressed. The focus is on synchronized in situ structural characterization combined with dielectric and electrical measurements. These methods are used to rigorously discriminate additive superposition of ER and MR responses from genuinely non-additive cross-field coupling. Finally, perspectives on applications and device-integration strategies for EMR-based components and systems are outlined.
The Casimir effect, a fundamental manifestation of quantum vacuum fluctuations, has evolved from a curiosity between idealized metallic plates to a versatile probe of quantum and material properties in structured and time-dependent media. This review traces the progression of Casimir force research from its classical formulation in noble metals like gold (Au) to cutting-edge developments involving metamaterials and time crystals. Beyond surveying recent experimental and theoretical advances, we provide a unifying framework that bridges Casimir physics with essential solid-state principles—including band theory, dielectric response, and temporal periodicity—critical for understanding forces in real and engineered materials. Special attention is given to non-equilibrium and dynamically modulated systems, where time-periodic structures can profoundly alter vacuum-induced interactions. By synthesizing insights from quantum field theory and condensed matter physics, this review offers a comprehensive perspective on the rich interplay between quantum fluctuations, material response, and temporal symmetry breaking.
Primordial black holes (PBHs) may have formed in the early Universe and may account for all or part of the dark matter. In this review, we summarize the current observational constraints on PBHs across the full mass range, highlight potential evidence for their existence, and outline the prospects for future searches, particularly with gravitational-wave observatories. We also discuss different PBH formation scenarios, identify the corresponding mass functions, and present the observational constraints in each case.
