Three-party dense coding with a GHZ state
= Three-party dense coding with a GHZ state
If two senders share a GHZ state with a receiver, one sender can encode two bits with $X^xZ^z$ and the other one bit with $X^b$. Sending both qubits to the receiver produces one of eight orthogonal GHZ-basis states, so a joint measurement recovers all three bits.