Control of state and state entanglement with a single auxiliary   subsystem
  We present a strategy to control the evolution of a quantum system. The novel aspect of this protocol is the use of a \emph{single auxiliary subsystem}. Two applications are given, one which allows for state preservation and another which controls the degree of entanglement of a given initial state. 
R. Rossi Jr., A. R. Bosco de Magalh\~aes, J.G. Peixoto de Faria and M.   C. Nemes