Exponential algorithmic speedup by quantum walk

Authors:
  • ACAndrew M. Childs
    Andrew M. Childs
  • RCRichard Cleve
    Richard Cleve
  • EDEnrico Deotto
    Enrico Deotto
  • EFEdward Farhi
    Edward Farhi
  • SGSam Gutmann
    Sam Gutmann
  • DSDaniel A. Spielman
    Daniel A. Spielman

Abstract
We construct an oracular problem that can be solved exponentially faster on a quantum computer than on a classical computer. The quantum algorithm is based on a continuous time quantum walk, and thus employs a different technique from previous quantum algorithms based on quantum Fourier transforms. We show how to implement the quantum walk efficiently in our oracular setting. We then show how this quantum walk can be used to solve our problem by rapidly traversing a graph. Finally, we prove that no classical algorithm can solve this problem with high probability in subexponential time.