Generation of Polarization‐Entangled Photon Pairs Based on Beam Displacers

Abstract The generation of high‐fidelity entangled states is crucial for quantum technologies, including quantum communication, quantum computing, and quantum metrology. Here, a polarization‐entangled photon‐pair source is demonstrated based on beam displacers and a type‐II periodically poled potassium titanyl phosphate crystal, employing a degenerate quasi‐phase‐matched spontaneous parametric down‐conversion process. The configuration features a fully linear architecture with a compact and robust design. Its performance is characterized by high‐visibility quantum interference fringes ( and ), high quantum state fidelity (), and significant violation of Bell inequality (). The system offers excellent stability, ease of alignment, and high integrability, making it suitable for operation in challenging and long‐term environments. In particular, quantum key distribution benefits from entangled photon sources with high fidelity to ensure secure and efficient information transmission.