  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.
