Quantum complexity of testing group commutativity

  • Authors:
  • Frédéric Magniez;Ashwin Nayak

  • Affiliations:
  • CNRS–LRI, UMR 8623 Université Paris–Sud, France;Institute for Theoretical Physics, University of Waterloo and Perimeter, Canada

  • Venue:
  • ICALP'05 Proceedings of the 32nd international conference on Automata, Languages and Programming
  • Year:
  • 2005

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Abstract

We consider the problem of testing the commutativity of a black-box group specified by its k generators. The complexity (in terms of k) of this problem was first considered by Pak, who gave a randomized algorithm involving O(k) group operations. We construct a quite optimal quantum algorithm for this problem whose complexity is in Õ(k2/3). The algorithm uses and highlights the power of the quantization method of Szegedy. For the lower bound of Ω(k2/3), we introduce a new technique of reduction for quantum query complexity. Along the way, we prove the optimality of the algorithm of Pak for the randomized model.