Direct generation of multi-photon hyperentanglement

TL;DR

This paper introduces direct protocols for generating multi-photon hyperentangled states without post-selection, enabling more practical quantum communication applications with higher efficiency and scalability.

Contribution

The authors develop new methods for directly producing multi-photon hyperentanglement using cascaded SPDC sources, extending to arbitrary photon numbers, and encoding in multiple degrees of freedom.

Findings

Achieved direct generation of three- and four-photon hyperentanglement.

Calculated generation rates under specific experimental parameters.

Eliminated the need for outcome post-selection in hyperentanglement production.

Abstract

Multi-photon hyperentangement is of fundamental importance in optical quantum information processing. Existing theory and experiment producing multi-photon hyperentangled states have until now relied on the outcome post-selection, a procedure where only the measurement results corresponding to the desired state are considered. Such approach severely limits the usefulness of the resulting hyperentangled states. We present the protocols of direct production of three- and four-photon hyperentanglement and extend the approach to an arbitrary number of photons through a straightforward cascade of spontaneous parametric down-conversion (SPDC) sources. The generated multi-photon hyperentangled states are encoded in polarization-spatial modes and polarization-time bin degrees of freedom, respectively. Numerical calculation shows that if the average photon number $\mu$ is set to 1, the down conversion efficiency is $7.6*10^{-6}$ and the repetition frequency of the laser is $10^9$ Hz, the number of the generation of three-photon and four-photon hyperentanglement after cascading can reach about $5.78*10^{-2}$ and $4.44*10^{-7}$ pairs per second, respectively. By eliminating the constraints of outcome post-selection, our protocols may represent important progresses for multi-photon hyperentangement generation and providing a pivotal role in future multi-party and high-capacity communication networks.