Generation of Polarization Entangled Photon Pairs in the Mid-Infrared and Visible Regions

Photon entanglement is essential for quantum communication, sensing, and computing. While research on frequency-degenerate entangled photons in the near-infrared (NIR) region has advanced significantly, entangled light spanning mid-infrared (MIR) and visible (VIS) frequencies remains under development [1]. For instance, in the MIR region, chiral collective lattice vibration modes that exhibit selectivity for circularly polarized light have been observed in two-dimensional layered materials [2], suggesting the existence of quantum entanglement with electronic states [3]. This entanglement could lead to the conservation of quantum states. For this purpose, it is necessary to generate quantum entangled states of photons in the MIR and VIS regions with high fidelity.