ABSTRACT
Suppose there is a stack of N unstructured files and we want to find a particular file (or files) out of the N files. To find someone’s phone number in a telephone directory is an easy structured datebase search problem, while to find a person’s name who has a particular phone number is a more difficult unstructured database seach problem, with which we are concerned in this chapter. It is required to take O(N) steps on average if a classical algorithm is employed. If we check the files one by one, we will hit the right file with probability 1/2 after N/2 files are examined. It turns out that this takes only O( √ N) steps with a quantum algorithm, first discovered by Grover [1, 2, 3].
Our presentation in this chapter closely follows [4] and [5].
