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One of the properties of Kondacs-Watrous model of quantum finite automata (QFA) is that the probability of the correct answer for a QFA cannot be amplified arbitrarily. In this paper, we determine the maximum probabilities achieved by QFAs…

Quantum Physics · Physics 2007-05-23 Andris Ambainis , Arnolds Kikusts

We prove a kind of a pumping lemma for languages accepted by one-register alternating finite-memory automata. As a corollary, we obtain that the set of lengths of words in such languages is semi-linear.

Formal Languages and Automata Theory · Computer Science 2025-12-30 Yoav Danieli

In the literature, there exist several quantum finite automata (QFA) models with both quantum and classical states. These models are of particular interest,as they show praiseworthy advantages over the fully quantum models in some…

Formal Languages and Automata Theory · Computer Science 2015-06-30 Lvzhou Li , Yuan Feng

We study the following decision problem: is the language recognized by a quantum finite automaton empty or non-empty? We prove that this problem is decidable or undecidable depending on whether recognition is defined by strict or non-strict…

Quantum Physics · Physics 2007-05-23 Vincent D. Blondel , Emmanuel Jeandel , Pascal Koiran , Natacha Portier

We present a language $L_n$ which is recognizable by a probabilistic finite automaton (PFA) with probability $1 - \epsilon$ for all $\epsilon > 0$ with $O(log^2n)$ states, with a deterministic finite automaton (DFA) with O(n) states, but a…

Quantum Physics · Physics 2007-05-23 Gatis Midrijanis

A new class of languages of infinite words is introduced, called the max-regular languages, extending the class of $\omega$-regular languages. The class has two equivalent descriptions: in terms of automata (a type of deterministic counter…

Formal Languages and Automata Theory · Computer Science 2009-03-09 Mikolaj Bojanczyk

In this note, we generalize the results of arXiv:0901.2703v1 We show that all one-way quantum finite automaton (QFA) models that are at least as general as Kondacs-Watrous QFA's are equivalent in power to classical probabilistic finite…

Computational Complexity · Computer Science 2010-09-20 Abuzer Yakaryilmaz , A. C. Cem Say

Quantum computing is a new model of computation, based on quantum physics. Quantum computers can be exponentially faster than conventional computers for problems such as factoring. Besides full-scale quantum computers, more restricted…

Formal Languages and Automata Theory · Computer Science 2018-07-05 Andris Ambainis , Abuzer Yakaryılmaz

The theory of computation is based on abstract computing automata which can be classified into a three-class hierarchy: Finite Automata (FA), Push-down Automata (PDA) and the Turing Machines (TM). Each class corresponds to grammar/language…

Emerging Technologies · Computer Science 2019-03-12 Marta Duenas-Diez , Juan Perez-Mercader

The potential of the exact quantum information processing is an interesting, important and intriguing issue. For examples, it has been believed that quantum tools can provide significant, that is larger than polynomial, advantages in the…

Formal Languages and Automata Theory · Computer Science 2014-11-26 Jozef Gruska , Daowen Qiu , Shenggen Zheng

B\"uchi's theorem states that $\omega$-regular languages are characterized as languages of the form $\bigcup_i U_i V_i^\omega$, where $U_i$ and $V_i$ are regular languages. Parikh automata are automata on finite words whose transitions are…

Formal Languages and Automata Theory · Computer Science 2023-02-09 Mario Grobler , Sebastian Siebertz

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…

Formal Languages and Automata Theory · Computer Science 2023-06-22 Aleksejs Naumovs , Maksims Dimitrijevs , Abuzer Yakaryılmaz

A quantitative word automaton (QWA) defines a function from infinite words to values. For example, every infinite run of a limit-average QWA A obtains a mean payoff, and every word w is assigned the maximal mean payoff obtained by…

Formal Languages and Automata Theory · Computer Science 2026-03-31 Thomas A. Henzinger , Pavol Kebis , Nicolas Mazzocchi , N. Ege Saraç

The two-way finite automaton with quantum and classical states (2QCFA), defined by Ambainis and Watrous, is a model of quantum computation whose quantum part is extremely limited; however, as they showed, 2QCFA are surprisingly powerful: a…

Computational Complexity · Computer Science 2021-01-06 Zachary Remscrim

In this paper we present a systematic view of Quantum Cellular Automata (QCA), a mathematical formalism of quantum computation. First we give a general mathematical framework with which to study QCA models. Then we present four different…

Quantum Physics · Physics 2007-05-23 Carlos A. Perez-Delgado , Donny Cheung

Families of DFAs (FDFAs) have recently been introduced as a new representation of $\omega$-regular languages. They target ultimately periodic words, with acceptors revolving around accepting some representation $u\cdot v^\omega$. Three…

Formal Languages and Automata Theory · Computer Science 2023-07-17 Yong Li , Sven Schewe , Qiyi Tang

We find an application in quantum finite automata for the ideas and results of [JL21] and [JL22]. We reformulate quantum finite automata with multiple-time measurements using the algebraic notion of near-ring. This gives a unified…

Formal Languages and Automata Theory · Computer Science 2022-04-21 George Jeffreys , Siu-Cheong Lau

Automata over infinite alphabets have emerged as a convenient computational model for processing structures involving data, such as nonces in cryptographic protocols or data values in XML documents. We introduce active learning methods for…

Formal Languages and Automata Theory · Computer Science 2026-03-27 Florian Frank , Stefan Milius , Jurriaan Rot , Henning Urbat

Infinite words over infinite alphabets serve as models of the temporal development of the allocation and (re-)use of resources over linear time. We approach omega-languages over infinite alphabets in the setting of nominal sets, and study…

Formal Languages and Automata Theory · Computer Science 2021-07-13 Henning Urbat , Daniel Hausmann , Stefan Milius , Lutz Schröder

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…

Computational Complexity · Computer Science 2014-01-29 A. C. Cem Say , Abuzer Yakaryilmaz