  We investigate in detail the effects of a QND vibrational number measurement
made on single ions in a recently proposed measurement scheme for the
vibrational state of a register of ions in a linear rf trap [C. D'Helon and
G.J. Milburn, Phys. Rev. A 54, 5141 (1996)]. The performance of a measurement
shows some interesting patterns which are closely related to searching.
