Experimental observation of entanglement duality for identical particles

TL;DR

This paper reports the first experimental observation of entanglement duality in identical photons, demonstrating how quantum indistinguishability leads to dual entanglement features that vanish as particles become distinguishable.

Contribution

It provides the first experimental verification of entanglement duality in identical particles, linking it directly to quantum indistinguishability.

Findings

Entanglement duality observed in photons with different labeling.

Duality disappears as photons become distinguishable.

Confirms entanglement duality as a quantum indistinguishability feature.

Abstract

It was shown recently that entanglement of identical particles has a feature called dualism [Phys. Rev. Lett. 110, 140404 (2013)], which is fundamentally connected with quantum indistinguishability. Here we report an experiment that observes the entanglement duality for the first time with two identical photons, which manifest polarization entanglement when labeled by different paths or path entanglement when labeled by polarization states. By adjusting the mismatch in frequency or arrival time of the entangled photons, we tune the photon indistinguishability from quantum to classical limit and observe that the entanglement duality disappears under emergence of classical distinguishability, confirming it as a characteristic feature of quantum indistinguishable particles.