# Entanglement A quantum correlation between particles that persists regardless of the distance separating them. When two [[Qubit]]s are entangled, measuring one instantly determines the state of the other — what Einstein dismissed as "spooky action at a distance." This is not communication faster than light (no information is transmitted), but it is a correlation that has no classical equivalent and that [[Quantum Computing]] algorithms exploit to outperform classical computation. Entanglement is the resource that makes quantum algorithms work. [[Shor's Algorithm]] and other quantum speedups depend on creating and manipulating entangled states across many qubits. The more qubits you can entangle while maintaining their coherence, the more powerful your quantum computer. [[Decoherence]] — the loss of entanglement through environmental interaction — is why scaling quantum computers is so difficult. In cryptography, entanglement enables Quantum Key Distribution: any attempt to eavesdrop on an entangled communication channel disturbs the quantum state, alerting the communicators. This is the basis of theoretically unbreakable quantum encryption. ## See Also - [[Qubit]] — the unit that gets entangled - [[Superposition]] — the other key quantum property - [[Decoherence]] — what breaks entanglement - [[Technology Lexicon]] — the full vocabulary (quantum computing section)