  Quantum computing is concerned with computer technology based on the
principles of quantum mechanics, with operations performed at the quantum
level. Quantum computational models make it possible to analyze the resources
required for computations. Quantum automata can be classified thusly: quantum
finite automata, quantum sequential machine, quantum pushdown automata, quantum
Turing machine and orthomodular lattice-valued automata. These models are
useful for determining the expressive power and boundaries of various
computational features. In light of the current state of quantum computation
theory research, a systematic review of the literature seems timely. This
article seeks to provide a comprehensive and systematic analysis of quantum
finite automata models, quantum finite automata models with density operators
and quantum finite automata models with classical states, interactive proof
systems, quantum communication complexity and query complexity as described in
the literature. The statistics of quantum finite automata related papers are
shown and open problems are identified for more advanced research. The current
status of quantum automata theory is distributed into various categories. This
research work also highlights the previous research, current status and future
directions of quantum automata models.
