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We introduce a novel hybrid quantum-classical algorithm for the near-term computation of expectation values in quantum systems at finite temperatures. This is based on two stages: on the first one, a mixed state approximating a fiducial…

Quantum Physics · Physics 2024-01-31 Giuseppe Clemente

This thesis explores the application of the Symmetry-Breaking/Symmetry-Restoration methodology on quantum computers to better approximate a Hamiltonian's ground state energy within a variational framework in many-body physics. This involves…

Quantum Physics · Physics 2023-11-10 Andres Ruiz

Bethe equations, whose solutions determine exact eigenvalues and eigenstates of corresponding integrable Hamiltonians, are generally hard to solve. We implement a Variational Quantum Eigensolver (VQE) approach to estimating Bethe roots of…

Quantum Physics · Physics 2025-01-28 David Raveh , Rafael I. Nepomechie

Recent research has shown that wavefunction evolution in real- and imaginary-time can generate quantum subspaces with significant utility for obtaining accurate ground state energies. Inspired by these methods, we propose combining quantum…

Calculations of molecular spectral properties, like photodissociation rates and absorption bands, rely on knowledge of the excited state energies of the molecule of interest. Protocols based on the variational quantum eigensolver (VQE) are…

Quantum Physics · Physics 2021-10-19 Yordan S. Yordanov , Crispin H. W. Barnes , David R. M. Arvidsson-Shukur

We propose a quantum-classical hybrid algorithm to simulate the non-equilibrium steady state of an open quantum many-body system, named the dissipative-system Variational Quantum Eigensolver (dVQE). To employ the variational optimization…

Quantum Physics · Physics 2020-12-07 Nobuyuki Yoshioka , Yuya O. Nakagawa , Kosuke Mitarai , Keisuke Fujii

The Variational Quantum Eigensolver (VQE) is a promising quantum algorithm for applications in chemistry within the Noisy Intermediate-Scale Quantum (NISQ) era. The ability for a quantum computer to simulate electronic structures with high…

We present the meta-VQE, an algorithm capable to learn the ground state energy profile of a parametrized Hamiltonian. By training the meta-VQE with a few data points, it delivers an initial circuit parametrization that can be used to…

Quantum Physics · Physics 2021-06-01 Alba Cervera-Lierta , Jakob S. Kottmann , Alán Aspuru-Guzik

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

The contextual subspace variational quantum eigensolver (CS-VQE) is a hybrid quantum-classical algorithm that approximates the ground-state energy of a given qubit Hamiltonian. It achieves this by separating the Hamiltonian into contextual…

Quantum Physics · Physics 2023-02-14 Alexis Ralli , Tim Weaving , Andrew Tranter , William M. Kirby , Peter J. Love , Peter V. Coveney

The Variational Quantum Eigensolver (VQE) is a promising candidate for quantum applications on near-term Noisy Intermediate-Scale Quantum (NISQ) computers. Despite a lot of empirical studies and recent progress in theoretical understanding…

Quantum Physics · Physics 2022-05-26 Xuchen You , Shouvanik Chakrabarti , Xiaodi Wu

Using quantum devices supported by classical computational resources is a promising approach to quantum-enabled computation. One example of such a hybrid quantum-classical approach is the variational quantum eigensolver (VQE) built to…

Quantum Physics · Physics 2017-04-12 Jarrod R. McClean , Mollie E. Schwartz , Jonathan Carter , Wibe A. de Jong

The adaptive derivative-assembled pseudo-trotter variational quantum eigensolver (ADAPT-VQE) is a promising hybrid quantum-classical algorithm for molecular ground state energy calculation, yet its practical scalability is hampered by…

Quantum Physics · Physics 2026-02-05 Runhong He , Xin Hong , Qiaozhen Chai , Ji Guan , Junyuan Zhou , Arapat Ablimit , Guolong Cui , Shenggang Ying

Solving interacting multi-particle systems is a central challenge in quantum chemistry and condensed matter physics. In this work, we investigate the computation of ground states and ground-state energies for the He-H+ and H2O molecules…

Quantum Physics · Physics 2026-01-08 Luca Ion , Adam Smith

Variational quantum eigensolvers (VQEs) combine classical optimization with efficient cost function evaluations on quantum computers. We propose a new approach to VQEs using the principles of measurement-based quantum computation. This…

Quantum spin systems may offer the first opportunities for beyond-classical quantum computations of scientific interest. While general quantum simulation algorithms likely require error-corrected qubits, there may be applications of…

The vacuum of the lattice Schwinger model is prepared on up to 100 qubits of IBM's Eagle-processor quantum computers. A new algorithm to prepare the ground state of a gapped translationally-invariant system on a quantum computer is…

Quantum Physics · Physics 2024-04-23 Roland C. Farrell , Marc Illa , Anthony N. Ciavarella , Martin J. Savage

The Variational Quantum Eigensolver (VQE) algorithm, as applied to finding the ground state of a Hamiltonian, is particularly well-suited for deployment on noisy intermediate-scale quantum (NISQ) devices. Here we utilize the VQE algorithm…

Quantum Physics · Physics 2024-11-28 Younes Javanmard , Ugne Liaubaite , Tobias J. Osborne , Xusheng Xu , Man-Hong Yung

Hybrid quantum-classical adaptive Variational Quantum Eigensolvers (VQE) hold the potential to outperform classical computing for simulating many-body quantum systems. However, practical implementations on current quantum processing units…

The variational quantum eigensolver (VQE) is a promising algorithm to compute eigenstates and eigenenergies of a given quantum system that can be performed on a near-term quantum computer. Obtaining eigenstates and eigenenergies in a…

Quantum Physics · Physics 2021-03-10 Kohdai Kuroiwa , Yuya O. Nakagawa