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We investigate ancilla-free linear combination of unitaries (LCU) as a framework for approximating complex quantum circuits. This is particularly effective for quantum optimization algorithms, where candidate solutions can be evaluated…

Quantum Physics · Physics 2026-05-20 Almudena Carrera Vazquez , Daniel J. Egger , Stefan Woerner

Although a universal quantum computer is still far from reach, the tremendous advances in controllable quantum devices, in particular with solid-state systems, make it possible to physically implement "quantum simulators". Quantum…

Quantum Physics · Physics 2016-06-08 Zhixin Wang , Xiu Gu , Lian-Ao Wu , Yu-xi Liu

We present a new approach to simulating Hamiltonian dynamics based on implementing linear combinations of unitary operations rather than products of unitary operations. The resulting algorithm has superior performance to existing simulation…

Quantum Physics · Physics 2018-08-02 Andrew M. Childs , Nathan Wiebe

The effective Hamiltonian serves as the conceptual pivot of quantum engineering, transforming physical complexity into programmable logic; yet, its construction remains compromised by the mathematical non-uniqueness of block…

Quantum Physics · Physics 2026-02-04 Hao-Yu Guan , Xiao-Long Zhu , Yu-Hang Dang , Xiu-Hao Deng

Electronic structure simulation is an anticipated application for quantum computers. Due to high-dimensional quantum entanglement in strongly correlated systems, the quantum resources required to perform such simulations are far beyond the…

Quantum Physics · Physics 2022-01-25 Jie Liu , Zhenyu Li , Jinlong Yang

The utility of effective model spaces in quantum simulations of non-relativistic quantum many-body systems is explored in the context of the Lipkin-Meshkov-Glick model of interacting fermions. We introduce an iterative…

Quantum Physics · Physics 2023-08-25 Caroline E. P. Robin , Martin J. Savage

We propose an iterative algorithm to simulate the dynamics generated by any $n$-qubit Hamiltonian. The simulation entails decomposing the unitary time evolution operator $U$ (unitary) into a product of different time-step unitaries. The…

Quantum Physics · Physics 2012-04-09 Ashok Ajoy , Rama Koteswara Rao , Anil Kumar , Pranaw Rungta

Modeling non-Hermitian Hamiltonians is increasingly important in classical and quantum domains, especially when studying open systems, $PT$ symmetry, and resonances. However, the quantum simulation of these models has been limited by the…

Quantum Physics · Physics 2025-02-20 Anastashia Jebraeilli , Michael R. Geller

Exploiting inherent symmetries is a common and effective approach to speed up the simulation of quantum systems. However, efficiently accounting for non-Abelian symmetries, such as the $SU(2)$ total-spin symmetry, remains a major challenge.…

Quantum Physics · Physics 2024-12-20 Anthony Gandon , Alberto Baiardi , Max Rossmannek , Werner Dobrautz , Ivano Tavernelli

We introduce a family of identities that express general linear non-unitary evolution operators as a linear combination of unitary evolution operators, each solving a Hamiltonian simulation problem. This formulation can exponentially…

Quantum Physics · Physics 2025-12-16 Dong An , Andrew M. Childs , Lin Lin

The capacity for solving eigenstates with a quantum computer is key for ultimately simulating physical systems. Here we propose inverse iteration quantum eigensolvers, which exploit the power of quantum computing for the classical inverse…

Quantum Physics · Physics 2022-03-09 Min-Quan He , Dan-Bo Zhang , Z. D. Wang

Implementing general functions of operators is a powerful tool in quantum computation. It can be used as the basis for a variety of quantum algorithms including matrix inversion, real and imaginary-time evolution, and matrix powers. Quantum…

Quantum Physics · Physics 2022-06-08 Thais de Lima Silva , Lucas Borges , Leandro Aolita

The Variational Quantum Eigensolver approach to the electronic structure problem on a quantum computer involves measurement of the Hamiltonian expectation value. Formally, quantum mechanics allows one to measure all mutually commuting or…

Quantum Physics · Physics 2020-03-17 Tzu-Ching Yen , Vladyslav Verteletskyi , Artur F. Izmaylov

Quantum computing is a promising technology that harnesses the peculiarities of quantum mechanics to deliver computational speedups for some problems that are intractable to solve on a classical computer. Current generation noisy…

Numerical Analysis · Mathematics 2022-09-16 Daan Camps , Efekan Kökcü , Lindsay Bassman , Wibe A. de Jong , Alexander F. Kemper , Roel Van Beeumen

Quantum machine learning (QML) is a discipline that seeks to transfer the advantages of quantum computing to data-driven tasks. However, many studies rely on toy datasets or heavy feature reduction, raising concerns about their scalability.…

Quantum Physics · Physics 2025-04-16 Federico Tiblias , Anna Schroeder , Yue Zhang , Mariami Gachechiladze , Iryna Gurevych

To treat a problem with a Quantum Processing Unit (QPU), it must be transformed into a sequence of quantum operations, or gates: this is the quantum description of the problem. These operations are either packed into a query (i.e. quantum…

Quantum Physics · Physics 2026-03-19 Robin Ollive , Stéphane Louise

Over the last century, a large number of physical and mathematical developments paired with rapidly advancing technology have allowed the field of quantum chemistry to advance dramatically. However, the lack of computationally efficient…

Quantum Physics · Physics 2011-03-08 James D. Whitfield , Jacob Biamonte , Alán Aspuru-Guzik

In a digital quantum simulator, basic two-qubit interactions are manipulated by means of fast local control operations to establish a desired target Hamiltonian. Here we consider a quantum simulator based on logical systems, i.e. where…

Quantum Physics · Physics 2023-02-08 Ferran Riera-Sàbat , Pavel Sekatski , Wolfgang Dür

Simulating the unitary dynamics of a quantum system is a fundamental problem of quantum mechanics, in which quantum computers are believed to have significant advantage over their classical counterparts. One prominent such instance is the…

Quantum Physics · Physics 2024-09-04 John M. Martyn , Yuan Liu , Zachary E. Chin , Isaac L. Chuang

Quantum computing has been increasingly applied in nuclear physics. In this work, we combine quantum computing with the complex scaling method to address the resonance problem. Due to the non-Hermiticity introduced by complex scaling,…

Nuclear Theory · Physics 2024-09-11 Hantao Zhang , Dong Bai , Zhongzhou Ren