Ambainis-Freivalds’ Algorithm for Measure-Once Automata
Aija Bērziņa5
and Richard Bonner6 
| (5) |
Institute of Math and Computer Science, University of Latvia, Raiņa bulvāris 29, LV-1459 Riga, Latvia |
| (6) |
Department of Mathematics and Physics, Malardalen University, Wasteras, Sweeden |
Abstract
An algorithm given by Ambainis and Freivalds [1] constructs a quantum finite automaton (QFA) with O(logp) states recognizing the language Lp = ai|i is divisible by p with probability 1 − ε, for any ε > 0 and arbitrary prime p. In [4] we gave examples showing that the algorithm is applicable also to quantum automata of very limited size. However, the Ambainis-Freivalds
algoritm is tailored to constructing a measure-many QFA (defined by Kondacs and Watrous [2]), which cannot be implemented on existing quantum computers. In this paper we modify the algorithm to construct a measure-once QFA of Moore and Crutchfield [3] and give examples of parameters for this automaton. We show for the language Lp that a measure-once QFA can be twice as space efficient as measure-many QFA’s.
Research supported by Grant No. 01.0354 from the Latvian Council of Science, Contract IST-1999-11234 (QAIP) from the European
Commission, and the Swedish Institute, Project ML-2000
Supported by the ML-2000 project sponsored by the Sweedish Institute
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