GHZ state

Multi-partite entanglement

The W state is, in a certain sense, "less entangled" than the GHZ state; however, that entanglement is more robust against qubit loss, in the sense that a 3-qubit W state remains a bipartite entangled state when one of the qubits is discarded. If one qubit is measured in the Z basis, the entanglement between the other two qubits is lost with probability 1/3, but is promoted to maximal entanglement with probability 2/3. By contrast, for the 3-qubit GHZ state, discarding a qubit results in a separable mixed state, and a Z measurement on a qubit will always leave behind a pure product state. Both the GHZ state and the W state can be generalized to systems with more than 3 qubits, and both retain their own characteristics: The N-qubit GHZ state becomes unentangled if even one qubit is lost, and the N-qubit W state keeps some entanglement even if only two qubits remain.