Quantum Walk Algorithm for Element Distinctness

  • Authors:
  • Andris Ambainis

  • Affiliations:
  • Princeton University

  • Venue:
  • FOCS '04 Proceedings of the 45th Annual IEEE Symposium on Foundations of Computer Science
  • Year:
  • 2004

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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 0(n^{{2 \mathord{\left/ {\vphantom {2 3}} \right. \kern-\nulldelimiterspace} 3}}) query quantum algorithm. This improves the previous 0(n^{{3 \mathord{\left/ {\vphantom {3 4}} \right. \kern-\nulldelimiterspace} 4}} ) quantum algorithm of Buhrman et al. [10] and matches the lower bound by Shi [28]. We also give an 0(N^{{k \mathord{\left/ {\vphantom {k {(k + 1)}}} \right. \kern-\nulldelimiterspace} {(k + 1)}}} ) query quantum algorithm for the generalization of element distinctness in which we have to find k equal items among N items.