Simultaneous transmission of hyper-entanglement in 3 degrees of freedom through a multicore fiber

TL;DR

This paper demonstrates the simultaneous transmission of hyper-entangled photon pairs in energy-time and polarization degrees of freedom across multicore fibers, achieving high fidelity and enabling integration with existing telecom infrastructure for advanced quantum communication.

Contribution

It introduces a method to transmit hyper-entanglement in multiple degrees of freedom through multicore fibers, maintaining high fidelity and path entanglement across cores.

Findings

Achieved at least 95% fidelity to Bell states in all degrees of freedom.

Successfully transmitted hyper-entangled photons across multiple fiber cores.

Compatible with standard telecommunication wavelengths for practical quantum networks.

Abstract

Entanglement distribution is at the heart of most quantum communication protocols. Inevitable loss of photons along quantum channels is a major obstacle for distributing entangled photons over long distances, as the no-cloning theorem forbids the information to simply be amplified along the way as is done in classical communication. It is therefore desirable for every successfully transmitted photon pair to carry as much entanglement as possible. Spontaneous parametric down-conversion (SPDC) creates photons entangled in multiple high-dimensional degrees of freedom simultaneously, often referred to as hyper-entanglement. In this work, we use a multicore fibre (MCF) to show that energy-time and polarization degrees of freedom can simultaneously be transmitted in multiple fibre cores, even maintaining path entanglement across the cores. We verify a fidelity to the ideal Bell state of at least 95$\%$ in all degrees of freedom. Furthermore, because the entangled photons are created with a center wavelength of 1560 nm, our approach can readily be integrated into modern telecommunication infrastructure, thus paving the way for high-rate quantum key distribution and many other entanglement-based quantum communication protocols.