Advancements in Entangled Photon Pairs in 2D Van der Waal Materials for On‐Chip Quantum Device Applications

ABSTRACT The next generation of technology is rooted in quantum‐based advancements. The entangled photon pair (EPP) sources play a pivotal role in such a wide range of advancements in quantum‐based device applications, including quantum‐ high‐precision sensors, communication, computing, cryptography, and so on. The bulk nonlinear crystals continue to dominate the current landscape of EPPs generation. However, emerging 2D quantum materials have demonstrated remarkable breakthroughs in both quantum photonics, nonlinear optics, and EPPs generation compared to conventional crystals. Their phase‐matching‐free spontaneous parametric down‐conversion (SPDC), ultrashort coherence length, lowest crystal symmetry, exceptionally large and anisotropic second‐order nonlinear susceptibility (), and seamless compatibility with on‐chip, silicon‐based photonic integration positions them as highly promising candidates for EPPs generation and next‐generation quantum photonic and quantum device technologies. This review article highlights recent breakthroughs and advancements in the generation of EPPs in 2D van der Waals (vdW) materials, with a focus on their applicability to quantum technologies and plausible on‐chip quantum integrated photonic device technology. The article begins by discussing the fundamental principles of EPPs generation. It provides a comprehensive review of the origin and generation of entangled photons in emerging layered vdW materials, alongside various optical quantum characterization techniques. The review then explores key physical parameters of the quantum states associated with EPPs. Additionally, it examines concepts related to the realization of paired photon generation at the quantum limit. The final section focuses on the potential for on‐chip integrated quantum device applications. Beyond highlighting recent advancements in quantum‐based research, the review also outlines the current limitations and future prospects aimed at advancing the field.