Today I read a paper titled “1-way quantum finite automata: strengths, weaknesses and generalizations”
The abstract is:
We study 1-way quantum finite automata (QFAs).
First, we compare them with their classical counterparts.
We show that, if an automaton is required to give the correct answer with a large probability (over 0.98), then the power of 1-way QFAs is equal to the power of 1-way reversible automata.
However, quantum automata giving the correct answer with smaller probabilities are more powerful than reversible automata.
Second, we show that 1-way QFAs can be very space-efficient.
Namely, we construct a 1-way QFA which is exponentially smaller than any equivalent classical (even randomized) finite automaton.
This construction may be useful for design of other space-efficient quantum algorithms.
Third, we consider several generalizations of 1-way QFAs.
Here, our goal is to find a model which is more powerful than 1-way QFAs keeping the quantum part as simple as possible..