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Variational quantum algorithms on bosonic quantum processors are an emerging paradigm for quantum chemistry calculations, exploiting the natural alignment between molecular structure and harmonic oscillator-based hardware. We introduce the…

Quantum Physics · Physics 2026-04-21 Marlon F. Jost , Sijia S. Dong

Near-term quantum computers are expected to facilitate material and chemical research through accurate molecular simulations. Several developments have already shown that accurate ground-state energies for small molecules can be evaluated…

Variational Quantum optimization algorithms, such as the Variational Quantum Eigensolver (VQE) or the Quantum Approximate Optimization Algorithm (QAOA), are among the most studied quantum algorithms. In our work, we evaluate and improve an…

Quantum Physics · Physics 2022-10-24 David Winderl , Nicola Franco , Jeanette Miriam Lorenz

The superiority of variational quantum algorithms (VQAs) such as quantum neural networks (QNNs) and variational quantum eigen-solvers (VQEs) heavily depends on the expressivity of the employed ansatze. Namely, a simple ansatze is…

Quantum Physics · Physics 2022-03-14 Yuxuan Du , Zhuozhuo Tu , Xiao Yuan , Dacheng Tao

Computing the excited states of a given Hamiltonian is computationally hard for large systems, but methods that do so using quantum computers scale tractably. This problem is equivalent to the PCA problem where we are interested in…

Quantum Physics · Physics 2025-03-19 David Quiroga , Jason Han , Anastasios Kyrillidis

Variational quantum algorithms (VQAs) are prominent candidates for near-term quantum advantage but lack rigorous guarantees of convergence and generalization. By contrast, quantum phase estimation (QPE) provides provable performance under…

Quantum Physics · Physics 2025-10-09 Tuyen Nguyen , Mária Kieferová

In this work we present a detailed analysis of variational quantum phase estimation (VQPE), a method based on real-time evolution for ground and excited state estimation on near-term hardware. We derive the theoretical ground on which the…

Quantum computational chemistry has emerged as an important application of quantum computing. Hybrid quantum-classical computing methods, such as variational quantum eigensolvers (VQE), have been designed as promising solutions to quantum…

Determining the ground state of a many-body Hamiltonian is a central problem across physics, chemistry, and combinatorial optimization, yet it is often classically intractable due to the exponential growth of Hilbert space with system size.…

Quantum Physics · Physics 2026-02-24 Jungyun Lee , Daniel K. Park

Harnessing the full power of nascent quantum processors requires the efficient management of a limited number of quantum bits with finite lifetime. Hybrid algorithms leveraging classical resources have demonstrated promising initial results…

The rapid progress in quantum computing has opened up new possibilities for tackling complex scientific problems. Variational quantum eigensolver (VQE) holds the potential to solve quantum chemistry problems and achieve quantum advantages.…

Quantum Physics · Physics 2024-03-08 Linghua Zhu , Senwei Liang , Chao Yang , Xiaosong Li

Level spectroscopy stands as a powerful method for identifying the transition point that delineates distinct quantum phases. Since each quantum phase exhibits a characteristic sequence of excited states, the crossing of energy levels…

The hardware requirements of useful quantum algorithms remain unmet by the quantum computers available today. Because it was designed to soften these requirements, the Variational Quantum Eigensolver (VQE) has gained popularity as a…

Quantum Physics · Physics 2022-12-09 Mafalda Ramôa

The Variational Quantum Eigensolver (VQE) is a hybrid quantum-classical algorithm for computing ground state energies of molecular systems. We implement VQE to calculate the potential energy surface of the hydrogen molecule (H$_2$) across…

Quantum Physics · Physics 2026-01-16 Rylan Malarchick , Ashton Steed

We propose the unitary variational quantum-neural hybrid eigensolver (U-VQNHE), which improves upon the original VQNHE by enforcing unitary neural transformations. The non-unitary nature of VQNHE causes normalization issues and divergence…

Quantum Physics · Physics 2026-03-06 Minwoo Kim , Kyoung Keun Park , Uihwan Jeong , Sangyeon Lee , Taehyun Kim

Variational quantum algorithm (VQA), which is comprised of a classical optimizer and a parameterized quantum circuit, emerges as one of the most promising approaches for harvesting the power of quantum computers in the noisy intermediate…

Quantum Physics · Physics 2021-12-01 Samuel Stein , Yufei Ding , Nathan Wiebe , Bo Peng , Karol Kowalski , Nathan Baker , James Ang , Ang Li

The quantum-classical hybrid Variational Quantum Eigensolver (VQE) algorithm is recognized to be the most suitable approach to obtain ground state energies of quantum many-body systems in the noisy intermediate scale quantum era. In this…

Atomic Physics · Physics 2023-04-12 K. R. Swain , V. S. Prasannaa , Kenji Sugisaki , B. P. Das

Variational quantum eigensolver (VQE), aiming at determining the ground state energy of a quantum system described by a Hamiltonian on noisy intermediate scale quantum (NISQ) devices, is among the most significant applications of…

Quantum Physics · Physics 2024-04-12 Ze-Tong Li , Fan-Xu Meng , Han Zeng , Zai-Chen Zhang , Xu-Tao Yu

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

Quantum Computing is believed to be the ultimate solution for quantum chemistry problems. Before the advent of large-scale, fully fault-tolerant quantum computers, the variational quantum eigensolver~(VQE) is a promising heuristic quantum…

Quantum Physics · Physics 2023-12-06 Chu Guo , Yi Fan , Zhiqian Xu , Honghui Shang