How does quantum entanglement enable quantum communication?

Quantum entanglement enables quantum communication by creating a fundamental link between particles that allows information to be transmitted or verified in ways that classical physics cannot achieve. When two particles become entangled, their quantum states are correlated so that measuring one instantly determines the state of the other, regardless of the distance between them. This property, called non-locality, forms the basis for protocols like quantum key distribution (QKD), where entangled particles generate shared secrets between two parties. For example, in the E91 protocol, pairs of entangled photons are sent to separate parties. By measuring their photons using randomly chosen bases, they can later compare a subset of results to detect eavesdropping—since any interception would disturb the entangled state, revealing the intrusion.

A key application of entanglement is quantum teleportation, which transfers the state of a qubit from one location to another without physically moving the particle. This relies on pre-shared entanglement: if Alice and Bob share an entangled pair, Alice can perform a joint measurement on her half of the pair and the qubit she wants to teleport. The result of this measurement is sent classically to Bob, who uses it to transform his half of the entangled pair into the original qubit’s state. While this process requires classical communication to complete, the entanglement ensures the qubit’s state is recreated exactly, avoiding the no-cloning theorem. This mechanism is foundational for quantum networks, enabling distributed quantum computing or secure communication between nodes.

Practically, entanglement-based communication faces challenges like decoherence and signal loss over long distances. Current implementations often use photons transmitted through fiber optics or free space. For instance, China’s Micius satellite demonstrated entanglement distribution over 1,200 kilometers, leveraging the vacuum of space to minimize interference. To scale further, quantum repeaters are being developed to extend entanglement through a chain of nodes, using entanglement swapping to link segments. Developers working on these systems must address noise, latency, and error rates—problems familiar in classical networking but amplified in quantum contexts. While still experimental, these efforts highlight entanglement’s role in building future communication infrastructures that prioritize security and quantum-state transfer.