Device-independent quantum key distribution (DI-QKD) represents one of the most fascinating challenges in quantum communication, exploiting concepts of fundamental physics, namely Bell tests of nonlocality, to ensure the security of a communication link. This requires the loophole-free violation of a Bell inequality, which is intrinsically difficult due to losses in fibre optic transmission channels. Heralded photon amplification is a teleportation-based protocol that has been proposed as a means to overcome transmission loss for DI-QKD. Here we demonstrate heralded photon amplification for path entangled states and characterise the entanglement before and after loss by exploiting a recently developed displacement-based detection scheme. We demonstrate that by exploiting heralded photon amplification we are able to reliably maintain high fidelity entangled states over loss-equivalent distances of more than 50~km.
@article{arxiv.1612.01802,
title = {Heralded Amplification of Path Entangled Quantum States},
author = {F. Monteiro and E. Verbanis and V. Caprara Vivoli and A. Martin and N. Gisin and H. Zbinden and R. T. Thew},
journal= {arXiv preprint arXiv:1612.01802},
year = {2016}
}