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In a standard Grover's algorithm for quantum searching, the probability of finding the marked item is not exactly 1. In this paper we present a modified version of Grover's algorithm that searches a marked state with full successful rate. The modification is done by replacing the phase inversion by phase rotation through angle. The rotation angle is given analytically to be =2arcsin (sin/ (4J+6) /sin), where sin=1/N, N is the number of items in the database, and J is any integer equal to or greater than the integer part of (/2) -/ (2). Upon measurement at the (J+1) th iteration, the marked state is obtained with certainty.
Gui‐Lu Long (Wed,) studied this question.