Quantum Walk Algorithm for Element Distinctness

  • Authors:
  • Andris Ambainis

  • Affiliations:
  • -

  • Venue:
  • SIAM Journal on Computing
  • Year:
  • 2007

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Abstract

We use quantum walks to construct a new quantum algorithm for element distinctness and its generalization. For element distinctness (the problem of finding two equal items among $N$ given items), we get an $O(N^{2/3})$ query quantum algorithm. This improves the previous $O(N^{3/4})$ quantum algorithm of Buhrman et al. [SIAM J. Comput., 34 (2005), pp. 1324-1330] and matches the lower bound of Aaronson and Shi [J. ACM, 51 (2004), pp. 595-605]. We also give an $O(N^{k/(k+1)})$ query quantum algorithm for the generalization of element distinctness in which we have to find $k$ equal items among $N$ items.