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文章基本信息

  • 标题:The weakness of CTC qubits and the power of approximate counting
  • 本地全文:下载
  • 作者:Ryan O'Donnell ; A. C. Cem Say
  • 期刊名称:Electronic Colloquium on Computational Complexity
  • 印刷版ISSN:1433-8092
  • 出版年度:2016
  • 卷号:2016
  • 出版社:Universität Trier, Lehrstuhl für Theoretische Computer-Forschung
  • 摘要:

    We present two results in structural complexity theory concerned with the following interrelated topics: computation with postselection/restarting, closed timelike curves (CTCs), and approximate counting. The first result is a new characterization of the lesser known complexity class BPP_path in terms of more familiar concepts. Precisely, BPP_path is the class of problems that can be efficiently solved with a nonadaptive oracle for the Approximate Counting problem. Our second result is concerned with the computational power conferred by CTCs; or equivalently, the computational complexity of finding stationary distributions for quantum channels. We show that any poly(n)-time quantum computation using a CTC of O(log n) qubits may as well just use a CTC of 1 classical bit. This result essentially amounts to showing that one can find a stationary distribution for a poly(n)-dimensional quantum channel in PP.

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