Grover close-quote s quantum searching algorithm is optimal

I show that for any number of oracle lookups up to about π/4√ (N) , Grover close-quote s quantum searching algorithm gives the maximal possible probability of finding the desired element. I explain why this is also true for quantum algorithms which use measurements during the computation. I also show that unfortunately quantum searching cannot be parallelized better than by assigning different parts of the search space to independent quantum computers. copyright 1999 The American Physical Society