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In the molecular quantum chemistry community, coupled-cluster (CC) methods are well-recognized for their systematic convergence and reliability. The extension of the theory to extended systems has been comparably recent, so that…

Chemical Physics · Physics 2024-10-31 Andreas Grüneis , Evgeny Moerman , Matthias Scheffler , Tonghao Shen , Igor Ying Zhang

We introduce a hybrid quantum-classical algorithm, the localized active space unitary selective coupled cluster singles and doubles (LAS-USCCSD) method. Derived from the localized active space unitary coupled cluster (LAS-UCCSD) method,…

Simulating molecules using the Variational Quantum Eigensolver method is one of the promising applications for NISQ-era quantum computers. Designing an efficient ansatz to represent the electronic wave function is crucial in such…

Chemical Physics · Physics 2022-05-09 Dmitry A. Fedorov , Yuri Alexeev , Stephen K. Gray , Matthew Otten

Molecular simulations are widely regarded as leading candidates to demonstrate quantum advantage--defined as the point at which quantum methods surpass classical approaches in either accuracy or scale. Yet the qubit counts and error rates…

We propose a practical method for accurately evaluating molecular energies using a hybrid approach that integrates fault-tolerant quantum computers with classical computing. Our scheme comprises two complementary methods: quantum dominant…

Quantum Physics · Physics 2026-03-04 Nobuki Inoue , Hisao Nakamura

We introduce the multistate iterative qubit coupled cluster (MS-iQCC) method, a quantum-inspired algorithm that runs efficiently on classical hardware and is designed to predict both ground and excited electronic states of molecules.…

Chemical Physics · Physics 2026-01-05 Robert A. Lang , Shashank G. Mehendale , Ilya G. Ryabinkin , Artur F. Izmaylov

The practical application of quantum technologies to chemical problems faces significant challenges, particularly in the treatment of realistic basis sets and the accurate inclusion of electron correlation effects. A direct approach to…

Hybrid quantum-classical approaches offer potential solutions to quantum chemistry problems, yet they often manifest as constrained optimization problems. Here, we explore the interconnection between constrained optimization and generalized…

Quantum Physics · Physics 2025-03-27 Muqing Zheng , Bo Peng , Ang Li , Xiu Yang , Karol Kowalski

Simultaneous quantum-classical communications (SQCC) protocols are a family of continuous-variable quantum key distribution (CV-QKD) protocols which allow for quantum and classical symbols to be integrated concurrently on the same optical…

Quantum Physics · Physics 2026-02-03 Nicholas Zaunders , Ziqing Wang , Robert Malaney , Ryan Aguinaldo , Timothy C. Ralph

We present a perturbative triples correction to the relativistic quadratic unitary coupled cluster singles and doubles (qUCCSD) method, denoted as qUCCSD[T]. The method builds upon the Hermitian structure of the unitary ansatz and employs a…

Chemical Physics · Physics 2025-10-08 Kamal Majee , Ján Šimunek , Jozef Noga , Achintya Kumar Dutta

Numerous numerical studies have shown that geminal-based methods are a promising direction to model strongly correlated systems with low computational costs. Several strategies have been introduced to capture the missing dynamical…

Chemical Physics · Physics 2023-03-22 Artur Nowak , Katharina Boguslawski

We propose an orbital optimized method for unitary coupled cluster theory (OO-UCC) within the variational quantum eigensolver (VQE) framework for quantum computers. OO-UCC variationally determines the coupled cluster amplitudes and also…

Strongly Correlated Electrons · Physics 2020-09-23 Wataru Mizukami , Kosuke Mitarai , Yuya O. Nakagawa , Takahiro Yamamoto , Tennin Yan , Yu-ya Ohnishi

The unitary coupled cluster (UCC) approximation is one of the more promising wave-function ans\"atze for electronic structure calculations on quantum computers via the variational quantum eigensolver algorithm. However, for large systems…

Quantum Physics · Physics 2021-09-30 Jia Chen , Hai-Ping Cheng , James K. Freericks

The Quantum Charge-Coupled Device (QCCD) architecture is a modular design to expand trapped-ion quantum computer that relies on the coherent shuttling of qubits across an array of segmented electrodes. Leveraging trapped ions for their long…

Quantum Physics · Physics 2025-05-05 Chenghong Zhu , Xian Wu , Jingbo Wang , Xin Wang

An iterative version of the qubit coupled cluster (QCC) method [I.G. Ryabinkin et al., J. Chem. Theory Comput. 14, 6317 (2019)] is proposed. The new method seeks to find ground electronic energies of molecules on noisy intermediate-scale…

Quantum Physics · Physics 2019-10-28 Ilya G. Ryabinkin , Robert A. Lang , Scott N. Genin , Artur F. Izmaylov

Although quantum computing offers a promising solution for strongly correlated system simulation, existing algorithms face significant bottlenecks on current noisy intermediate-scale quantum (NISQ) devices. Here, we introduce…

Sample-based quantum diagonalization (SQD) is a hybrid quantum-classical algorithm for estimating ground-state energies in electronic-structure calculations. It uses a quantum processor as a sampler to construct a variational subspace, with…

Quantum Physics · Physics 2026-04-21 Byeongyong Park , Sanha Kang , Jongseok Seo , Juhee Baek , Doyeol Ahn , Keunhong Jeong

Time-dependent coupled-cluster method with time-varying orbital functions, called time-dependent optimized coupled- cluster (TD-OCC) method, is formulated for multielectron dynamics in an intense laser field. We have successfully derived…

Chemical Physics · Physics 2018-03-14 Takeshi Sato , Himadri Pathak , Yuki Orimo , Kenichi L. Ishikawa

Circuit depth reduction is of critical importance for quantum chemistry simulations on current and near term quantum computers. This issue is tackled by introducing a chemically aware strategy for the Unitary Coupled Cluster ansatz. The…

The cluster state model for quantum computation [Phys. Rev. Lett. 86, 5188] outlines a scheme that allows one to use measurement on a large set of entangled quantum systems in what is known as a cluster state to undertake quantum…

Quantum Physics · Physics 2007-05-23 William Hall