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}
}
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It has been proved that a language which cannot be recognizing by any one-way and multi-letter quantum finite automata can be recognized by two-way quantum finite Automata with two heads and it has been investigated that quantum variant of two- way deterministic multihead finite automaton takes less number of heads to recognize a language containing of all words whose length is a prime number.
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The Limitations of Few Qubits: One-way and Two-way Quantum Finite Automata and the Group Word Problem
The two-way finite automaton with quantum and classical states (2QCFA), defined by Ambainis and Watrous, is a model of quantum computation whose quantum part is extremely limited; however, as they…
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