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Ab initio electronic excited state calculations are necessary for the quantitative study of photochemical reactions, but their accurate computation on classical computers is plagued by prohibitive scaling. The Variational Quantum Deflation…

The advantage that many quantum algorithms have over their classical counterparts may be lost when the results are extracted as classical data (output problem). One example are eigenpair solvers, which encode the eigenpairs in a quantum…

Quantum Physics · Physics 2025-11-13 Sven Danz

Preparing the ground states of a many-body system is essential for evaluating physical quantities and determining the properties of materials. This work provides a quantum ground state preparation scheme with shallow variational warm-start…

Quantum Physics · Physics 2023-03-21 Youle Wang , Chenghong Zhu , Mingrui Jing , Xin Wang

Variational calculations of excited electronic states are carried out by finding saddle points on the surface that describes how the energy of the system varies as a function of the electronic degrees of freedom. This approach has several…

Chemical Physics · Physics 2023-02-15 Yorick L. A. Schmerwitz , Gianluca Levi , Hannes Jónsson

We demonstrate that, rather than resorting to high-cost dynamic correlation methods, qualitative failures in excited-state potential energy surface predictions can often be remedied at no additional cost by ensuring that optimal molecular…

Chemical Physics · Physics 2020-06-18 Lan Nguyen Tran , Eric Neuscamman

We propose a general scheme for dissipatively preparing arbitrary pure quantum states on a multipartite qubit register in a finite number of basic control blocks. Our "splitting-subspace" approach relies on control resources that are…

Quantum Physics · Physics 2013-11-19 Giacomo Baggio , Francesco Ticozzi , Lorenza Viola

The iterative quantum phase estimation algorithm, applied to calculating the ground state energies of quantum chemical systems, is theoretically appealing in its wide scope of being able to handle both weakly and strongly correlated…

Quantum Physics · Physics 2021-11-11 Dipanjali Halder , Srinivasa Prasannaa V. , Valay Agarawal , Rahul Maitra

In this work, we report an algorithm that is able to tailor qubit interactions for individual variational quantum algorithm problems. Here, the algorithm leverages the unique ability of a neutral atom tweezer platform to realize arbitrary…

Quantum Physics · Physics 2026-03-04 Robert de Keijzer , Luke Visser , Oliver Tse , Servaas Kokkelmans

In designing quantum control, it is generally required to simulate the controlled system evolution with a classical computer. However, computing the time evolution operator can be quite resource-consuming since the total Hamiltonian is…

Quantum Physics · Physics 2022-10-25 Xiaodong Yang , Xinfang Nie , Yunlan Ji , Tao Xin , Dawei Lu , Jun Li

Quantum dynamics can be analyzed via the structure of energy eigenstates. However, in the many-body setting, preparing eigenstates associated with finite temperatures requires time scaling exponentially with system size. In this work we…

Quantum Physics · Physics 2024-07-11 Samuel J. Garratt , Soonwon Choi

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

We explore the application of quantum optimal control (QOC) techniques to state preparation of lattice field theories on quantum computers. As a first example, we focus on the Schwinger model, quantum electrodynamics in 1+1 dimensions. We…

Quantum Physics · Physics 2025-02-12 Jack Y. Araz , Siddhanth Bhowmick , Matt Grau , Thomas J. McEntire , Felix Ringer

The variational quantum eigensolver (VQE) is one of the most promising algorithms for low-lying eigenstates calculation on Noisy Intermediate-Scale Quantum (NISQ) computers. Specifically, VQE has achieved great success for ground state…

Numerical Analysis · Mathematics 2025-12-19 Hengzhun Chen , Yingzhou Li , Bichen Lu , Jianfeng Lu

Ground-state preparation for a given Hamiltonian is a common quantum-computing task of great importance and has relevant applications in quantum chemistry, computational material modeling, and combinatorial optimization. We consider an…

Quantum Physics · Physics 2022-10-18 Yu-Qin Chen , Shi-Xin Zhang , Chang-Yu Hsieh , Shengyu Zhang

We introduce a quantum algorithm to efficiently prepare states with a small energy variance at the target energy. We achieve it by filtering a product state at the given energy with a Lorentzian filter of width $\delta$. Given a local…

Quantum Physics · Physics 2024-07-03 Reinis Irmejs , Mari Carmen Bañuls , J. Ignacio Cirac

We introduce a variational algorithm based on the quantum alternating operator ansatz (QAOA) for the approximate solution of computationally hard counting problems. Our algorithm, dubbed VQCount, is based on the equivalence between random…

Quantum Physics · Physics 2026-04-16 Julien Drapeau , Shreya Banerjee , Stefanos Kourtis

Within the present noisy intermediate-scale quantum-computing era, hybrid quantum-classical-processor algorithms have emerged as promising avenues for tackling electronic-structure eigenproblems. Among them, the so-called…

Quantum Physics · Physics 2026-05-21 Christophe Soule , Bruno Senjean , Benjamin Lasorne

We propose quantum-selected configuration interaction (QSCI), a class of hybrid quantum-classical algorithms for calculating the ground- and excited-state energies of many-electron Hamiltonians on noisy quantum devices. Suppose that an…

Quantum Physics · Physics 2023-02-23 Keita Kanno , Masaya Kohda , Ryosuke Imai , Sho Koh , Kosuke Mitarai , Wataru Mizukami , Yuya O. Nakagawa

Determining the spectrum and wave functions of excited states of a system is crucial in quantum physics and chemistry. Low-depth quantum algorithms, such as the Variational Quantum Eigensolver (VQE) and its variants, can be used to…

Advances in quantum simulator technology is increasingly required because research on quantum algorithms is becoming more sophisticated and complex. State vector simulation utilizes CPU and memory resources in computing nodes exponentially…

Quantum Physics · Physics 2024-09-04 Mikio Morita , Yoshinori Tomita , Junpei Koyama , Koichi Kimura