Entanglementbased

Entanglement-based refers to methods and experiments that use quantum entanglement as a fundamental resource for information processing, communication, and sensing. In contrast to prepare-and-measure approaches, entanglement-based schemes rely on correlations between entangled subsystems that cannot be explained by classical physics. These correlations enable tasks that would be impossible or less secure with separable states alone.

In quantum communication, entanglement-based protocols often implement quantum key distribution by distributing entangled particle pairs to two or more parties. The Ekert 1991 protocol (E91) uses entangled photon pairs and security is tied to a violation of a Bell inequality. Real networks rely on sources such as spontaneous parametric down-conversion and channels like optical fibers or free space. Experimental advances include loophole-free Bell tests and the pursuit of device-independent security, where the security of the key is tied to observed nonlocal correlations rather than trust in the devices; practical device-independent quantum key distribution remains technically demanding.

In quantum computing and networking, entanglement serves as a resource for teleportation, entanglement swapping, and measurement-based quantum computation, where computation proceeds through measurements on a highly entangled resource state such as a cluster state. Entanglement swapping enables extending entanglement across distant nodes, a key capability for quantum repeaters and long-distance networks. Entangled states also underpin quantum metrology, enabling precision measurements beyond classical limits.

Challenges for entanglement-based approaches include generating high-quality entanglement, preserving coherence in the presence of noise and loss, and providing robust security proofs under realistic conditions. The concept encompasses a broad class of protocols unified by the central role of entanglement as a nonlocal quantum resource.