Hyperentanglement concentration for two-photon four-qubit systems with linear optics

TL;DR

This paper presents efficient linear-optics protocols for concentrating hyperentangled two-photon four-qubit states in known and unknown parameter scenarios, enhancing long-distance quantum communication capabilities.

Contribution

It introduces a parameter-splitting method for known states and two Schmidt projection-based protocols for unknown states, all feasible with current technology.

Findings

Parameter-splitting method is highly efficient for known states.

Protocols are feasible with current linear optical technology.

Methods improve hyperentanglement concentration for quantum communication.

Abstract

Hyperentanglement, defined as the entanglement in several degrees of freedom (DOFs) of a quantum system, has attracted much attention recently. Here we investigate the possibility of concentrating the two-photon four-qubit systems in partially hyperentangled states in both the spatial mode and the polarization DOFs with linear optics. We first introduce our parameter-splitting method to concentrate the systems in the partially hyperentangled states with known parameters, including partially hyperentangled Bell states and cluster states. Subsequently, we present another two nonlocal hyperentanglement concentration protocols (hyper-ECPs) for the systems in partially hyperentangled unknown states, resorting to the Schmidt projection method. It will be shown that our parameter-splitting method is very efficient for the concentration of the quantum systems in partially entangled states with known parameters, resorting to linear-optical elements only. All these four hyper-ECPs are feasible with current technology and they may be useful in long-distance quantum communication based on hyperentanglement as they require only linear optical elements.