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Clifford gates and transformations, which map products of elementary Pauli or Majorana operators to other such products, are foundational in quantum computing, underpinning the stabilizer formalism, error-correcting codes, magic state…

Quantum Physics · Physics 2025-10-29 Ilias Magoulas , Francesco A. Evangelista

We examine the following problem: given a collection of Clifford gates, describe the set of unitaries generated by circuits composed of those gates. Specifically, we allow the standard circuit operations of composition and tensor product,…

Quantum Physics · Physics 2022-06-15 Daniel Grier , Luke Schaeffer

Bosonic Gaussian unitaries are fundamental building blocks of central continuous-variable quantum technologies such as quantum-optic interferometry and bosonic error-correction schemes. In this work, we present the first time-efficient…

Quantum Physics · Physics 2025-10-08 Marco Fanizza , Vishnu Iyer , Junseo Lee , Antonio A. Mele , Francesco A. Mele

It is well known in quantum optics that any process involving the preparation of a multimode gaussian state, followed by a gaussian operation and gaussian measurements, can be efficiently simulated by classical computers. Here, we provide…

Quantum Physics · Physics 2025-08-22 Michael G. Jabbour , Leonardo Novo

Gaussian processes are a versatile framework for learning unknown functions in a manner that permits one to utilize prior information about their properties. Although many different Gaussian process models are readily available when the…

Fermionic Gaussian states (FGSs) and the associated matchgate circuits play a central role in quantum information theory and condensed matter physics. Despite being possibly highly entangled, they can still be efficiently simulated on…

Quantum Physics · Physics 2026-03-09 Marc Langer , Raúl Morral-Yepes , Adam Gammon-Smith , Frank Pollmann , Barbara Kraus

We propose a new framework of topological complexity to study the computational complexity of quantum circuits and tensor networks. Within this framework, we establish the Quon Classical Simulation (QCS) for hybrid Clifford-Matchgate…

Quantum Physics · Physics 2025-08-11 Zixuan Feng , Zhengwei Liu , Fan Lu , Ningfeng Wang

The term Clifford group was introduced in 1998 by D. Gottesmann in his investigation of quantum error-correcting codes. The simplest Clifford group in multiqubit quantum computation is generated by a restricted set of unitary Clifford gates…

Quantum Physics · Physics 2018-10-25 J. Tolar

Bayesian methods in machine learning, such as Gaussian processes, have great advantages com-pared to other techniques. In particular, they provide estimates of the uncertainty associated with a prediction. Extending the Bayesian approach to…

Quantum Physics · Physics 2019-05-20 Zhikuan Zhao , Alejandro Pozas-Kerstjens , Patrick Rebentrost , Peter Wittek

In the framework of the supervised learning of a real function defined on a space X , the so called Kriging method stands on a real Gaussian field defined on X. The Euclidean case is well known and has been widely studied. In this paper, we…

Machine Learning · Statistics 2020-02-14 François Bachoc , Baptiste Broto , Fabrice Gamboa , Jean-Michel Loubes

In an ordinary quantum algorithm the gates are applied in a fixed order on the systems. The introduction of indefinite causal structures allows to relax this constraint and control the order of the gates with an additional quantum state. It…

Quantum Physics · Physics 2022-06-15 Martin J. Renner , Časlav Brukner

It is usually assumed that a quantum computation is performed by applying gates in a specific order. One can relax this assumption by allowing a control quantum system to switch the order in which the gates are applied. This provides a more…

Quantum Physics · Physics 2020-06-11 Mateus Araújo , Fabio Costa , Časlav Brukner

Matchgates are a restricted set of two-qubit gates known to be classically simulable under particular conditions. Specifically, if a circuit consists only of nearest-neighbour matchgates, an efficient classical simulation is possible if…

Quantum Physics · Physics 2016-06-24 Daniel J. Brod

It is known that every (single-qudit) Clifford operator maps the full set of generalized Pauli matrices (GPMs) to itself under unitary conjugation, which is an important quantum operation and plays a crucial role in quantum computation and…

Quantum Physics · Physics 2026-03-03 Cai-Hong Wang , Jiang-Tao Yuan , Zhi-Hao Ma , Shao-Ming Fei , Shang-Quan Bu

The required set of operations for universal continuous-variable quantum computation can be divided into two primary categories: Gaussian and non-Gaussian operations. Furthermore, any Gaussian operation can be decomposed as a sequence of…

Quantum Physics · Physics 2020-02-12 Kunal Sharma , Mark M. Wilde

The experimental realization of increasingly complex quantum states underscores the pressing need for new methods of state learning and verification. In one such framework, quantum state tomography, the aim is to learn the full quantum…

Quantum Physics · Physics 2025-01-30 Antonio Anna Mele , Yaroslav Herasymenko

Simulating generic quantum states and dynamics is practically intractable using classical computers. However, certain special classes -- namely Clifford and matchgate circuits -- permit efficient computation. They provide invaluable tools…

Quantum Physics · Physics 2025-05-13 Byungmin Kang , Chen Zhao , Zhengwei Liu , Xun Gao , Soonwon Choi

We show that the Clifford gates and stabilizer circuits in the quantum computing literature, which admit efficient classical simulation, are equivalent to affine signatures under a unitary condition. The latter is a known class of tractable…

Computational Complexity · Computer Science 2017-05-03 Jin-Yi Cai , Heng Guo , Tyson Williams

We define a class of stochastic processes based on evolutions and measurements of quantum systems, and consider the complexity of predicting their long-term behavior. It is shown that a very general class of decision problems regarding…

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

The Gottesman-Knill theorem asserts that quantum circuits composed solely of Clifford gates can be efficiently simulated classically. This theorem hinges on the fact that Clifford gates map Pauli strings to other Pauli strings, thereby…

Quantum Physics · Physics 2024-07-30 George Biswas