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Entanglement

Entanglement

January 3, 2025

Entanglement appears when a multi-qubit state cannot be written as a tensor product of single-qubit states.

Bell state example

A canonical entangled state is

Φ+=12(00+11). \lvert \Phi^+ \rangle = \frac{1}{\sqrt{2}} \left( \lvert 00 \rangle + \lvert 11 \rangle \right).

Measuring both qubits in the computational basis always yields either 00 or 11, with equal probability.

Entanglement is a resource for protocols such as superdense coding and quantum teleportation, and it plays a central role in many algorithms.

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Read about Measurement.