Faithful entanglement purification for high-capacity quantum communication with two-photon four-qubit systems

TL;DR

This paper introduces a theoretical scheme for faithful hyperentanglement purification in two-photon systems, enabling high-capacity quantum communication by correcting errors across multiple degrees of freedom with robust quantum circuits.

Contribution

It presents the first fidelity-robust hyperentanglement purification protocol for two-photon systems, utilizing quantum circuits that convert errors into detectable failures.

Findings

Efficient correction of bit-flip errors in polarization and spatial modes.

Maximal hyperentanglement achievable through multiple purification rounds.

Error robustness ensures fidelity despite practical scattering effects.

Abstract

As the hyperentanglement of photon systems presents lots of unique opportunities in high-capacity quantum networking, the hyperentanglement purification protocol (hyper-EPP) becomes a vital project work and the quality of its accomplishment attracts much attention recently. Here we present the first theoretical scheme of faithful hyper-EPP for nonlocal two-photon systems in two degrees of freedom (DOFs) by constructing several fidelity-robust quantum circuits for hyper-encoded photons. With this faithful hyper-EPP, the bit-flip errors in both the polarization and spatial-mode DOFs can be efficiently corrected and the maximal hyperentanglement in two DOFs could be in principle achieved by performing the hyper-EPP multiple rounds. Moreover, the fidelity-robust quantum circuits, parity-check quantum nondemolition detectors, and SWAP gates make this hyper-EPP works faithfully as the errors coming from practical scattering, in these quantum circuits, are converted into a detectable failure rather than infidelity. Furthermore, this hyper-EPP can be directly extended to purify photon systems entangled in single polarization or spatial-mode DOF and that hyperentangled in polarization and multiple-spatial-mode DOFs.