On the power of one-way automata with quantum and classical states

We consider the model of one-way automata with quantum and classical states (qcfas) introduced in [23]. We show, by a direct approach, that qcfas with isolated cut-point accept regular languages only, thus characterizing their computational power. Moreover, we give a size lower bound for qcfas accepting regular languages, and we explicitly build qcfas accepting the word quotients and inverse homomorphic images of languages accepted by given qcfas with isolated cut-point, maintaining the same cut-point, isolation, and polynomially increasing the size.