 They showed that only phase super-sensitivity is an unambiguous indicator of a NOON state; furthermore they introduced criteria for determining if it has been achieved based on the observed visibility and efficiency.Phase super sensitivity of NOON states with "N" = 2 was demonstrated and super resolution, but not super sensitivity as the efficiency was too low, of NOON states up to "N" = 4 photons was also demonstrated experimentally.NOON states were first introduced by Barry C. Sanders in the context of studying quantum decoherence in Schrödinger cat states.