Quantum Entanglement
A quantum phenomenon where two or more particles become correlated such that the state of one instantly determines the state of the other, regardless of distance.
Quantum entanglement is a phenomenon in which two or more quantum particles become correlated in a way that has no classical analogue. When particles are entangled, the quantum state of each particle cannot be described independently, so measuring one particle instantly determines the state of the other, no matter how far apart they are.
Entanglement is a resource in quantum computing. Two-qubit quantum gates create entanglement between qubits, allowing quantum computers to process information in ways that classical computers cannot efficiently simulate.
Einstein famously called entanglement 'spooky action at a distance' and used it in an argument against quantum mechanics. Subsequent experiments, particularly those of John Bell in the 1960s and experimental confirmations in the 1980s through today, have confirmed that entanglement is a real feature of nature.