Quantum Message Disruption: A Two-State Model
  A game in which one player makes unitary transformations of a simple system, and another seeks to confound the resulting state by a randomly chosen action is analyzed carefully. It is shown that the second player can reduce any system to a completely random one by rotation through an angle of 120 degrees, about an axis chosen at random. If, on the other hand, the second player is forced to behave ``classically'' by reducing the wave function, then the first play retains an advantage, which the second player may eliminate by repeated measurement using randomly selected bases. 
Paul B. Kantor