Telecom-band Hyperentangled Photon Pairs from a Fiber-based Source

TL;DR

This paper reports the experimental generation of telecom-band hyperentangled photon pairs in polarization and frequency using a fiber-based source, enabling advanced quantum communication protocols over existing fiber networks.

Contribution

It demonstrates a fiber-based source producing telecom-band hyperentangled photons in polarization and frequency, with high entanglement quality and simultaneous verification of both DoFs.

Findings

Entanglement concurrence above 0.95 for both DoFs

Successful simultaneous verification of polarization and frequency entanglement

Potential for implementing dense coding and high-dimensional QKD

Abstract

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