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We prove that quantum Turing machines are strictly superior to probabilistic Turing machines in function computation for any space bound $ o(\log(n)) $.

Computational Complexity · Computer Science 2010-09-17 A. C. Cem Say , Abuzer Yakaryilmaz

We find a modification to QMA where having one quantum proof is strictly less powerful than having two unentangled proofs, assuming EXP $\ne$ NEXP. This gives a new route to prove QMA(2) = NEXP that overcomes the primary drawback of a…

Quantum Physics · Physics 2024-10-28 Roozbeh Bassirian , Bill Fefferman , Itai Leigh , Kunal Marwaha , Pei Wu

We propose a quantum authentication and digital signature protocol whose security is founded on the Quantum Merlin Arthur~(QMA)-completeness of the consistency of local density matrices. The protocol functions as a true public-key…

Quantum Physics · Physics 2025-06-23 Le-Ran Liu , Min-Quan He , Dan-Bo Zhang , Z. D. Wang

A proof of quantumness is a type of challenge-response protocol in which a classical verifier can efficiently certify the quantum advantage of an untrusted prover. That is, a quantum prover can correctly answer the verifier's challenges and…

Quantum Physics · Physics 2022-09-21 Zhenning Liu , Alexandru Gheorghiu

This paper studies whether quantum proofs are more powerful than classical proofs, or in complexity terms, whether QMA=QCMA. We prove three results about this question. First, we give a "quantum oracle separation" between QMA and QCMA. More…

Quantum Physics · Physics 2020-09-30 Scott Aaronson , Greg Kuperberg

We introduce a simple sub-universal quantum computing model, which we call the Hadamard-classical circuit with one-qubit (HC1Q) model. It consists of a classical reversible circuit sandwiched by two layers of Hadamard gates, and therefore…

Quantum Physics · Physics 2018-11-19 Tomoyuki Morimae , Yuki Takeuchi , Harumichi Nishimura

Complexity theory typically focuses on the difficulty of solving computational problems using classical inputs and outputs, even with a quantum computer. In the quantum world, it is natural to apply a different notion of complexity, namely…

Quantum Physics · Physics 2025-04-07 Hugo Delavenne , François Le Gall , Yupan Liu , Masayuki Miyamoto

We consider the time and space required for quantum computers to solve a wide variety of problems involving matrices, many of which have only been analyzed classically in prior work. Our main results show that for a range of linear algebra…

Computational Complexity · Computer Science 2025-11-03 Paul Beame , Niels Kornerup , Michael Whitmeyer

Affine automata provide a finite-state computational model that preserves the linear-algebraic structure of quantum computation while operating entirely over the reals. Recent work has shown that affine automata can far surpass classical…

Formal Languages and Automata Theory · Computer Science 2026-05-04 Zeyu Chen , Junde Wu

A quantum position-verification scheme attempts to verify the spatial location of a prover. The prover is issued a challenge with quantum and classical inputs and must respond with appropriate timings. We consider two well-studied…

Quantum Physics · Physics 2025-01-22 Vahid Asadi , Richard Cleve , Eric Culf , Alex May

We prove the following facts about the language recognition power of quantum Turing machines (QTMs) in the unbounded error setting: QTMs are strictly more powerful than probabilistic Turing machines for any common space bound $ s $…

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

We propose an efficient scheme for verifying quantum computations in the `high complexity' regime i.e. beyond the remit of classical computers. Previously proposed schemes remarkably provide confidence against arbitrarily malicious…

Quantum Physics · Physics 2017-05-24 Richard Jozsa , Sergii Strelchuk

In this paper we consider a quantum computational variant of nondeterminism based on the notion of a quantum proof, which is a quantum state that plays a role similar to a certificate in an NP-type proof. Specifically, we consider quantum…

Computational Complexity · Computer Science 2007-05-23 John Watrous

The paper tackles the issue of $\textit{checking}$ that all copies of a large data set replicated at several nodes of a network are identical. The fact that the replicas may be located at distant nodes prevents the system from verifying…

Distributed, Parallel, and Cluster Computing · Computer Science 2021-10-05 Pierre Fraigniaud , François Le Gall , Harumichi Nishimura , Ami Paz

We study quantum algorithms that are given access to trusted and untrusted quantum witnesses. We establish strong limitations of such algorithms, via new techniques based on Laurent polynomials (i.e., polynomials with positive and negative…

Quantum Physics · Physics 2021-03-18 Scott Aaronson , Robin Kothari , William Kretschmer , Justin Thaler

In this paper we explore the power of AM for the case that verifiers are {\em two-way finite automata with quantum and classical states} (2QCFA)--introduced by Ambainis and Watrous in 2002--and the communications are classical. It is of…

Computational Complexity · Computer Science 2015-05-05 Shenggen Zheng , Daowen Qiu , Jozef Gruska

In recent years, many computational tasks have been proposed as candidates for showing a quantum computational advantage, that is an advantage in the time needed to perform the task using a quantum instead of a classical machine.…

Quantum Physics · Physics 2021-02-12 Federico Centrone , Niraj Kumar , Eleni Diamanti , Iordanis Kerenidis

We explore the possibility of accelerating the formal verification of classical programs with a quantum computer. A common source of security flaws stems from the existence of common programming errors like use after free, null-pointer…

Quantum Physics · Physics 2026-05-06 Sebastian Issel , Kilian Tscharke , Pascal Debus

We consider the task of verifying the correctness of quantum computation for a restricted class of circuits which contain at most two basis changes. This contains circuits giving rise to the second level of the Fourier Hierarchy, the lowest…

Quantum Physics · Physics 2018-04-18 Tommaso F. Demarie , Yingkai Ouyang , Joseph F. Fitzsimons

Although polynomial-time probabilistic Turing machines can utilize uncomputable transition probabilities to recognize uncountably many languages with bounded error when allowed to use logarithmic space, it is known that such "magic coins"…

Computational Complexity · Computer Science 2014-12-01 A. C. Cem Say , Abuzer Yakaryilmaz