Dense Coding with Extended GHZ-W State via Local Measurements

Two schemes, with entanglement concentration and via generalized measurement, for dense coding are investigated by using a extended four-qubit GHZ-W state, where the supervisors (David and Cliff) can control the average amount of information transmitted from the sender (Alice) to the receiver (Bob) by adjusting the measurement angles θ ₃ and θ ₄. We show that the results for the average amounts of information are unique from the different two schemes.