Controlled quantum secret sharing

We present a new protocol in which a secret multiqubit quantum state vertical bar Psi > is shared by n players and m controllers, where vertical bar Psi > is the encoding state of a quantum secret sharing scheme. The players may be considered as field agents responsible for carrying out a task, using the secret information encrypted in vertical bar Psi >, while the controllers are superiors who decide if and when the task should be carried out and who to do it. Our protocol only requires ancillary Bell states and Bell- basis measurements.