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A reduced-complexity variant of equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) method is formulated in terms of state-averaged excited state pair natural orbitals (PNO) designed to describe manifolds of excited states.…

Chemical Physics · Physics 2020-06-09 Chong Peng , Marjory C. Clement , Edward F. Valeev

Arguably the most widely used approaches for obtaining highly accurate molecular ground-state energies are coupled cluster methods. Despite introducing two layers of approximation, a linear and a nonlinear one, coupled cluster methods…

Numerical Analysis · Mathematics 2026-05-22 Jonas Beck , Benjamin Stamm

Resource-efficient and high-precision approximate synthesis of quantum circuits expressed in the Clifford+T gate set is vital for Fault-Tolerant quantum computing. Efficient optimal methods are known for single-qubit RZ unitaries, otherwise…

Quantum Physics · Physics 2026-04-27 Mathias Weiden , Justin Kalloor , John Kubiatowicz , Ed Younis , Costin Iancu

We find the ground-state energy of the Ising model using the Cascaded Variational Quantum Eigensolver (CVQE) algorithm with the Guided-Sampling Ansatz (GSA) using up to 63 qubits on a quantum computer. We study a heavy-hex lattice to match…

Quantum Physics · Physics 2026-04-29 John P. T. Stenger , C. Stephen Hellberg , Daniel Gunlycke

We introduce a quantum Monte Carlo inspired reweighting scheme to accurately compute energies from optimally short quantum circuits. This effectively hybrid quantum-classical approach features both entanglement provided by a short quantum…

Quantum Physics · Physics 2019-10-07 Guglielmo Mazzola , Pauline Ollitrault , Panagiotis Barkoutsos , Ivano Tavernelli

This study examines several techniques to improve the efficiency of the linearized multireference driven similarity renormalization group truncated to one- and two-body operators [MR-LDSRG(2)]. We propose a sequential MR-LDSRG(2)…

Chemical Physics · Physics 2019-03-29 Tianyuan Zhang , Chenyang Li , Francesco A. Evangelista

Within the framework of imaginary-time evolution for matrix product states, we introduce a cluster version of the infinite time-evolving block decimation algorithm for simulating quantum many-body systems, addressing the computational…

Strongly Correlated Electrons · Physics 2025-09-01 Tao Yang , Rui Wang , Z. Y. Xie , Baigeng Wang

We introduce a sum-of-squares SDP hierarchy approximating the ground-state energy from below for quantum many-body problems, with a natural quantum embedding interpretation. We establish the connections between our approach and other…

Quantum Physics · Physics 2023-05-31 Bowen Li , Jianfeng Lu

The unitary coupled cluster (UCC) ansatz is a promising tool for achieving high-precision results using the variational quantum eigensolver (VQE) algorithm in the NISQ era. However, results on quantum hardware are thus far very limited and…

Quantum Physics · Physics 2024-11-27 Mark R. Hirsbrunner , Diana Chamaki , J. Wayne Mullinax , Norm M. Tubman

Ground state preparation is a central application of quantum algorithms for electronic structure. We introduce the classical reservoir approach, a low cost variational ansatz tailored to near-term hardware, requiring only nearest-neighbor…

Quantum Physics · Physics 2025-12-25 Zekun He , Dominika Zgid , A. F. Kemper , J. K. Freericks

Shallow, CNOT-efficient quantum circuits are crucial for performing accurate computational chemistry simulations on current noisy quantum hardware. Here, we explore the usefulness of non-iterative energy corrections, based on the method of…

Chemical Physics · Physics 2023-05-03 Ilias Magoulas , Francesco A. Evangelista

The emerging field of quantum simulation of many-body systems is widely recognized as a very important application of quantum computing. A crucial step towards its realization in the context of many-electron systems requires a rigorous…

Atomic Physics · Physics 2021-08-23 Sumeet , V. S. Prasannaa , B. P. Das , B. K. Sahoo

We present the first application to real molecular systems of the recently proposed linear-response theory for the density-based basis-set correction method [J. Chem. Phys. 158, 234107 (2023)]. We apply this approach to accelerate the…

Chemical Physics · Physics 2024-02-27 Diata Traore , Julien Toulouse , Emmanuel Giner

Density functional theory (DFT) is the most widely used method for calculating molecular properties; however, its accuracy is often insufficient for quantitative predictions. Coupled-cluster (CC) theory is the most successful method for…

We propose a single-layer tensor network framework for the variational determination of ground states in two-dimensional quantum lattice models. By combining the nested tensor network method [Phys. Rev. B 96, 045128 (2017)] with the…

Strongly Correlated Electrons · Physics 2026-04-17 Hongyu Chen , Yangfeng Fu , Weiqiang Yu , Rong Yu , Z. Y. Xie

Determining ground state energies of quantum systems by hybrid classical/quantum methods has emerged as a promising candidate application for near-term quantum computational resources. Short of large-scale fault-tolerant quantum computers,…

Quantum Physics · Physics 2016-10-25 Nicholas C. Rubin

We present unrestricted Hartree Fock method coupled with configuration interaction (CI) method (URHF-CI) suitable for the calculation of ground and excited states of large number of electrons localized by complex gate potentials in…

Mesoscale and Nanoscale Physics · Physics 2009-11-11 Ramin M. Abolfath , Pawel Hawrylak

Quantum many-body systems pose a formidable computational challenge due to the exponential growth of their Hilbert space. While machine learning (ML) has shown promise as an alternative paradigm, most applications remain at the…

Disordered Systems and Neural Networks · Physics 2026-02-03 Yilun Gao , Alberto Rodríguez , Rudolf A. Römer

A relativistic version of the coupled-cluster single-double (CCSD) method is developed for atoms with a single valence electron. In earlier work, a linearized version of the CCSD method (with extensions to include a dominant class of triple…

Atomic Physics · Physics 2009-11-13 Rupsi Pal , M. S. Safronova , W. R. Johnson , Andrei Derevianko , Sergey G. Porsev

To expand the existing QUEST database of accurate vertical transition energies [\href{https://doi.org/10.1002/wcms.1517}{V\'eril et al.~\textit{WIREs Comput.~Mol.~Sci.} \textbf{2021}, \textit{11}, e1517}], we have modeled more than 100…

Chemical Physics · Physics 2024-01-26 Pierre-François Loos , Denis Jacquemin