Quantum entanglement is a physical phenomenon that occurs when a group of particles is generated, interact, or share spatial proximity in a way such that the quantum state of each particle of the group cannot be described independently of the state of the others.

Even when the particles are separated by a large distance, measurements on one instantly correlate with measurements on the other, a feature Einstein famously called \"spooky action at a distance\". Modern experiments have confirmed this phenomenon repeatedly, forming the backbone of quantum computing and quantum cryptography.