Photonic realization of a quantum finite automaton

We describe a physical implementation of a quantum finite automaton that recognizes a well-known family of periodic languages. The realization exploits the polarization degree of freedom of single photons and their manipulation through linear optical elements. We use techniques of confidence amplification to reduce the acceptance error probability of the automaton. It is worth remarking that the quantum finite automaton we physically realize is not only interesting per se but it turns out to be a crucial building block in many quantum finite automaton design frameworks theoretically settled in the literature

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 [28]. We show, by a direct approach, that QCFAs with isolated cut-point accept regular languages only, thus characterizing their computational power. Concerning descriptional power, we quickly overview a size lower bound for QCFAs accepting regular languages, and address its optimality. Then, 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 only polynomially increasing the size

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