How fast can a quantum computer search?

Abstract

This paper gives a simple proof of why a quantum computer, despite being in all possible states simultaneously, needs at least 0.707 sqrt(N) queries to retrieve a desired item from an unsorted list of items. The proof is refined to show that a quantum computer would need at least 0.785 sqrt(N) queries. The quantum search algorithm needs precisely this many queries.

arXiv commentPostscript, 7 pages. This proof tries to give a simple argument why the search algorithm is optimal (This paper was originally put out on quant-ph on September 9, 1998, the present version has several important improvements)

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