On the Class of Languages Recognizable by 1-Way Quantum Finite Automata
It is an open problem to characterize the class of languages recognized by quantum finite automata (QFA). We examine some neces- sary and some sufficient conditions for a (regular) language to be recog- nizable by a QFA. For a subclass of regular languages we get a condition which is necessary and sufficient.
Also, we prove that the class of languages recognizable by a QFA is not closed under union or any other binary Boolean operation where both arguments are significant.
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