Heralded Amplification of Path Entangled Quantum States

TL;DR

This paper demonstrates heralded photon amplification for path entangled states, enabling the preservation of high-fidelity entanglement over distances exceeding 50 km, which is crucial for advancing device-independent quantum key distribution.

Contribution

The authors experimentally realize heralded photon amplification for path entangled states and characterize entanglement preservation after loss using displacement-based detection.

Findings

High-fidelity entangled states maintained over 50 km equivalent loss.

Heralded amplification effectively compensates for transmission losses.

Displacement-based detection scheme enables entanglement characterization.

Abstract

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.