Entanglement links the properties of two or more particles so that measuring one affects predictions about the other, even when they are separated by large distances.
Quantum key distribution (QKD) uses quantum states to detect eavesdropping: interception alters the state and introduces measurable errors. Entanglement-based protocols can distribute keys with strong security guarantees rooted in physics.
Real-world systems must handle signal loss, noisy channels, and practical device limitations, which is why current deployments often combine quantum methods with classical cryptographic infrastructure.