Telecom-band hyperentangled photon pairs from a fiber-based source

Hyperentanglement, the simultaneous and independent entanglement of quantum\nparticles in multiple degrees of freedom, is a powerful resource that can be\nharnessed for efficient quantum information processing. In photonic systems,\nthe two degrees of freedom (DoF) often used to carry quantum and classical\ninformation are polarization and frequency, thanks to their robustness in\ntransmission, both in free space and in optical fibers. Telecom-band\nhyperentangled photons generated in optical fibers are of particular interest\nbecause they are compatible with existing fiber-optic infrastructure, and can\nbe distributed over fiber networks with minimal loss. Here, we experimentally\ndemonstrate the generation of telecom-band biphotons hyperentangled in both the\npolarization and frequency DoFs using a periodically-poled silica fiber and\nobserve entanglement concurrences above 0.95 for both polarization and\nfrequency DOFs. Furthermore, by concatenating a Hong-Ou-Mandel interference\ntest for frequency entanglement and full state tomography for polarization\nentanglement in a single experiment, we can demonstrate simultaneous\nentanglement in both the polarization and frequency DOFs. The states produced\nby our hyperentanglement source can enable protocols such as dense coding and\nhigh-dimensional quantum key distribution.\n