# 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} }

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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## 124 Citations

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