Controlled emission of entangled multiphoton states from cascaded quantum wells

We propose a deterministic source of entangled multiphoton states based on spontaneous emission from a ladder of a cascaded quantum well structure. The coupling between the quantum wells enables a many-path evolution with the emission of photon-number combination states in three modes. The tripartite multiphoton state can be used for controlling the entanglement between two multiphoton modes by measuring the third. We further discuss an application as a qubit-pair source with an error-detection ancilla.