Polarization-entanglement conserving frequency conversion of photons

TL;DR

This paper demonstrates a robust and flexible method for coherently converting the frequency of polarization-entangled photons, preserving their entanglement for quantum network applications, verified by Bell inequality violation and high fidelity.

Contribution

It presents the first experimental demonstration of polarization-entanglement preserving frequency conversion, enabling better integration of quantum communication components.

Findings

Successful entanglement conversion verified by Bell inequality violation

Fidelity of entanglement transfer close to unity

Implementation is robust and practical for quantum networks

Abstract

Entangled photons play a pivotal role in the distribution of quantum information in quantum networks. However, the frequency bands for optimal transmission and storage of photons are not necessarily the same. Here we experimentally demonstrate the coherent frequency conversion of photons entangled in their polarization, a widely used degree of freedom in photonic quantum information processing. We verify the successful entanglement conversion by violating a Clauser-Horne-Shimony-Holt (CHSH) Bell inequality and fully confirm that our characterised fidelity of entanglement transfer is close to unity using both state and process tomography. Our implementation is robust and flexible, making it a practical building block for future quantum networks.