On the complexity of simulating space-bounded quantum computations

  • Authors:
  • John Watrous

  • Affiliations:
  • Department of Computer Science, University of Calgary, Calgary, Alberta, Canada

  • Venue:
  • Computational Complexity
  • Year:
  • 2004

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Abstract

This paper studies the space-complexity of predicting the long-term behavior of a class of stochastic processes based on evolutions and measurements of quantum mechanical systems. These processes generalize a wide range of both quantum and classical space-bounded computations, including unbounded error computations given by machines having algebraic number transition amplitudes or probabilities. It is proved that any space s quantum stochastic process from this class can be simulated probabilistically with unbounded error in space O(s), and therefore deterministically in space O(s2).