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Hybrid quantum-classical algorithms have been proposed to circumvent noise limitations in quantum computers. Such algorithms delegate only a calculation of the expectation value to the quantum computer. Among them, the Variational Quantum…

Strongly Correlated Electrons · Physics 2022-11-02 Baptiste Anselme Martin , Pascal Simon , Marko J. Rančić

The coupled cluster method is considered a gold standard in quantum chemistry, reliably giving energies that are exact within chemical accuracy (1.6 mHartree). However, even in the CCSD approximation, where the cluster operator is truncated…

Chemical Physics · Physics 2023-03-10 Simon Elias Schrader , Simen Kvaal

Quantum computers promise to revolutionize our ability to simulate molecules, and cloud-based hardware is becoming increasingly accessible to a wide body of researchers. Algorithms such as Quantum Phase Estimation and the Variational…

Quantum Physics · Physics 2021-12-21 Kyle Sherbert , Frank Cerasoli , Marco Buongiorno Nardelli

Quantum-inspired algorithms can deliver substantial speedups over classical state-of-the-art methods by executing quantum algorithms with tensor networks on conventional hardware. Unlike circuit models restricted to unitary gates, tensor…

We propose the variational quantum singular value decomposition based on encoding the elements of the considered { $N\times N$} matrix into the state of a quantum system of appropriate dimension. This method doesn't use the expansion of…

Quantum Physics · Physics 2025-08-05 Alexander I. Zenchuk , Wentao Qi , Junde Wu

We propose a hybrid quantum-classical approach to model continuous classical probability distributions using a variational quantum circuit. The architecture of the variational circuit consists of two parts: a quantum circuit employed to…

Quantum Physics · Physics 2019-01-04 Jonathan Romero , Alan Aspuru-Guzik

We implement the Multi-Reference Unitary Coupled Cluster Singles and Doubles (MR-UCCSD) model with a quantum circuit that conserves the particle number to study the ground state energies of LiH, BeH$_2$, and H$_6$. This approach simplifies…

Quantum Physics · Physics 2025-04-15 Di Wu , C. L. Bai , H. Sagawa , H. Q. Zhang

We assess the performance of the Quantum Flow (QFlow) algorithm employing cost-effective solvers based on the unitary coupled-cluster ansatz with single and double excitations (QFlow-SD). The resulting energies are benchmarked against those…

Chemical Physics · Physics 2026-05-05 Bhumika Jayee , Nathan M. Myers , Duo Song , Eric J. Bylaska , Karol Kowalski , Nicholas P. Bauman

Fault-tolerant quantum computation (FTQC) is essential to implement quantum algorithms in a noise-resilient way, and thus to enjoy advantages of quantum computers even with presence of noise. In FTQC, a quantum circuit is decomposed into…

Quantum Physics · Physics 2025-07-23 Kohdai Kuroiwa , Yuya O. Nakagawa

State preparation for quantum algorithms is crucial for achieving high accuracy in quantum chemistry and competing with classical algorithms. The localized active space unitary coupled cluster (LAS-UCC) algorithm iteratively loads a…

Quantum Physics · Physics 2023-06-08 Ruhee D'Cunha , Matthew Otten , Matthew R. Hermes , Laura Gagliardi , Stephen K. Gray

We study a hardware-efficient variational quantum algorithm ansatz tailored for the trapped-ion quantum simulator, HEA-TI. We leverage programmable single-qubit rotations and global spin-spin interactions among all ions, reducing the…

Quantum Physics · Physics 2024-07-04 J. -Z. Zhuang , Y. -K. Wu , L. -M. Duan

H\"uckel molecular orbital (HMO) theory provides a semi-empirical treatment of the electronic structure in conjugated {\pi}-electronic systems. A scalable system-agnostic execution of HMO theory on a quantum computer is reported here based…

Quantum Physics · Physics 2024-05-22 Harshdeep Singh , Sonjoy Majumder , Sabyashachi Mishra

We present an equation generator algorithm that utilizes second-quantized operators in normal order with respect to a correlated or non-correlated reference and the corresponding Wick theorem. The algorithm proposed here, written with…

Chemical Physics · Physics 2023-08-31 Raúl Quintero-Monsebaiz , Pierre-François Loos

The superpositional wave function oscillations for finite-time implementation of quantum algorithms modifies the desired interference required for quantum computing. We propose a scheme with trapped ultracold ion-pairs being qubits to…

Quantum Physics · Physics 2007-05-23 Feng Mang , Zhu Xiwen , Gao Kelin , Shi Lei

We present a four-component relativistic unitary coupled cluster method for molecules. We have used commutator-based non-perturbative approximation using the ''Bernoulli expansion'' to derive an approximation to the relativistic unitary…

Chemical Physics · Physics 2024-03-06 Kamal Majee , Tamoghna Mukhopadhyay , Malaya K. Nayak , Achintya Kumar Dutta

We present quantum algorithms, for Hamiltonians of linear combinations of local unitary operators, for Hamiltonian matrix-vector products and for preconditioning with the inverse of shifted reduced Hamiltonian operator that contributes to…

Quantum Physics · Physics 2020-09-09 Zhiyong Zhang

Near-term quantum devices require wavefunction ans\"atze that are expressive while also of shallow circuit depth in order to both accurately and efficiently simulate molecular electronic structure. While unitary coupled cluster (e.g.,…

In this work, we study the projective quantum eigensolver (PQE) approach to optimizing unitary coupled cluster wave functions on quantum hardware, as introduced in arXiv:2102.00345. The projective quantum eigensolver is a hybrid…

Quantum Physics · Physics 2026-01-28 Martin Plazanet , Thomas Ayral

In this study, we propose a new method for constrained combinatorial optimization using variational quantum circuits. Quantum computers are considered to have the potential to solve large combinatorial optimization problems faster than…

Quantum Physics · Physics 2025-07-15 Hyakka Nakada , Kotaro Tanahashi , Shu Tanaka

Conventional clustering methods based on pairwise affinity usually suffer from the concentration effect while processing huge dimensional features yet low sample sizes data, resulting in inaccuracy to encode the sample proximity and…

Machine Learning · Computer Science 2023-02-06 Hongmin Cai , Fei Qi , Junyu Li , Yu Hu , Yue Zhang , Yiu-ming Cheung , Bin Hu