Propagation-induced entanglement revival

TL;DR

This paper demonstrates that angle-OAM entanglement of photon pairs, unlike position-momentum entanglement, can revive after decay during propagation, even in turbulent environments, enabling long-distance quantum communication.

Contribution

The study reveals that angle-OAM entanglement can revive after decay during propagation, both theoretically and experimentally, even under strong turbulence conditions.

Findings

Entanglement in angle-OAM bases revives after initial decay.

Turbulence delays but does not prevent entanglement revival.

Revived entanglement persists over arbitrary distances.

Abstract

The practical implementation of free-space quantum information tasks requires entanglement to be sustained over long distances and in the presence of turbulent and noisy environments. The transverse position-momentum entanglement of photon pairs produced by parametric down-conversion has found several uses in quantum information science, however, it is not suitable for applications involving long-distance propagation as the entanglement decays very rapidly when photons propagate away from their source. Entanglement is lost after a few centimetres of propagation, and the effect becomes even more pronounced in turbulent environments. In contrast, in this article, we show that entanglement in the angle-orbital angular momentum (OAM) bases exhibits a remarkably different behaviour. As with the position-momentum case, initially, the angle-OAM entanglement decays with propagation, but as the photons continue to travel further from the source, the photons regain their strongly correlated behaviour, and the entanglement returns. We theoretically and experimentally demonstrate this behaviour and show that entanglement returns even in the presence of strong turbulence. The only effect of turbulence is to increase the propagation distance for revival, but once revived, the two photons remain entangled up to an arbitrary propagation distance. This work highlights the role that OAM-angle entanglement will play in applications where quantum information is shared over long distances.