Two-way finite automata with quantum and classical state

@article{Ambainis2002TwowayFA,
  title={Two-way finite automata with quantum and classical state},
  author={Andris Ambainis and John Watrous},
  journal={Theor. Comput. Sci.},
  year={2002},
  volume={287},
  pages={299-311}
}
  • A. Ambainis, J. Watrous
  • Published 16 November 1999
  • Computer Science, Mathematics, Physics
  • Theor. Comput. Sci.
We introduce 2-way finite automata with quantum and classical states (2qcfa's). This is a variant on the 2-way quantum finite automata (2qfa) model which may be simpler to implement than unrestricted 2qfa's; the internal state of a 2qcfa may include a quantum part that may be in a (mixed) quantum state, but the tape head position is required to be classical.We show two languages for which 2qcfa's are better than classical 2-way automata. First, 2qcfa's can recognize palindromes, a language that… 
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