Entanglement is a uniquely quantum link between two or more particles. When particles become entangled the particles share a single, joint quantum state. Measuring a property of one particle instantly determines the corresponding property of its entangled partner, no matter how far apart they are.
Einstein famously called this “spooky action at a distance,” and it remains one of the most counterintuitive features of quantum mechanics. Importantly, entanglement cannot be used to send information faster than light, but the correlations it creates are real and have been confirmed in countless experiments.
For quantum computing, entanglement is essential. It is the resource that multi-qubit gates create, and it is what allows a quantum processor to represent and manipulate correlations that a classical computer cannot efficiently track. In a silicon spin qubit device, neighbouring quantum dots are tuned so that their electrons interact, generating the entanglement that quantum algorithms rely on.