513 research outputs found
Quantum counter automata
The question of whether quantum real-time one-counter automata (rtQ1CAs) can
outperform their probabilistic counterparts has been open for more than a
decade. We provide an affirmative answer to this question, by demonstrating a
non-context-free language that can be recognized with perfect soundness by a
rtQ1CA. This is the first demonstration of the superiority of a quantum model
to the corresponding classical one in the real-time case with an error bound
less than 1. We also introduce a generalization of the rtQ1CA, the quantum
one-way one-counter automaton (1Q1CA), and show that they too are superior to
the corresponding family of probabilistic machines. For this purpose, we
provide general definitions of these models that reflect the modern approach to
the definition of quantum finite automata, and point out some problems with
previous results. We identify several remaining open problems.Comment: A revised version. 16 pages. A preliminary version of this paper
appeared as A. C. Cem Say, Abuzer Yakary{\i}lmaz, and \c{S}efika
Y\"{u}zsever. Quantum one-way one-counter automata. In R\={u}si\c{n}\v{s}
Freivalds, editor, Randomized and quantum computation, pages 25--34, 2010
(Satellite workshop of MFCS and CSL 2010
Superiority of one-way and realtime quantum machines and new directions
In automata theory, the quantum computation has been widely examined for
finite state machines, known as quantum finite automata (QFAs), and less
attention has been given to the QFAs augmented with counters or stacks.
Moreover, to our knowledge, there is no result related to QFAs having more than
one input head. In this paper, we focus on such generalizations of QFAs whose
input head(s) operate(s) in one-way or realtime mode and present many
superiority of them to their classical counterparts. Furthermore, we propose
some open problems and conjectures in order to investigate the power of
quantumness better. We also give some new results on classical computation.Comment: A revised edition with some correction
Uncountable realtime probabilistic classes
We investigate the minimum cases for realtime probabilistic machines that can
define uncountably many languages with bounded error. We show that logarithmic
space is enough for realtime PTMs on unary languages. On binary case, we follow
the same result for double logarithmic space, which is tight. When replacing
the worktape with some limited memories, we can follow uncountable results on
unary languages for two counters.Comment: 12 pages. Accepted to DCFS201
New results on classical and quantum counter automata
We show that one-way quantum one-counter automaton with zero-error is more
powerful than its probabilistic counterpart on promise problems. Then, we
obtain a similar separation result between Las Vegas one-way probabilistic
one-counter automaton and one-way deterministic one-counter automaton.
We also obtain new results on classical counter automata regarding language
recognition. It was conjectured that one-way probabilistic one blind-counter
automata cannot recognize Kleene closure of equality language [A. Yakaryilmaz:
Superiority of one-way and realtime quantum machines. RAIRO - Theor. Inf. and
Applic. 46(4): 615-641 (2012)]. We show that this conjecture is false, and also
show several separation results for blind/non-blind counter automata.Comment: 21 page
The minimal probabilistic and quantum finite automata recognizing uncountably many languages with fixed cutpoints
It is known that 2-state binary and 3-state unary probabilistic finite
automata and 2-state unary quantum finite automata recognize uncountably many
languages with cutpoints. These results have been obtained by associating each
recognized language with a cutpoint and then by using the fact that there are
uncountably many cutpoints. In this note, we prove the same results for fixed
cutpoints: each recognized language is associated with an automaton (i.e.,
algorithm), and the proofs use the fact that there are uncountably many
automata. For each case, we present a new construction.Comment: 12 pages, minor revisions, changing the format to "dmtcs-episciences"
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