Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:2309.09868

Quantum computation of $π\to π^*$ and $n \to π^*$ excited states of aromatic heterocycles

Maria A. Castellanos, Mário Motta, Julia E. Rice

Published Sep 18, 2023• 0 citations
arXivHTMLPDF

Abstract

The computation of excited electronic states is an important application for quantum computers. In this work, we simulate the excited state spectra of four aromatic heterocycles on IBM superconducting quantum computers, focusing on active spaces of $π\to π^*$ and $n \to π^*$ excitations. We approximate the ground state with the entanglement forging method, a qubit reduction technique that maps a spatial orbital to a single qubit, rather than two qubits. We then determine excited states using the quantum subspace expansion method. We showcase these algorithms on quantum hardware using up to 8 qubits and employing readout and gate error mitigation techniques. Our results demonstrate a successful application of quantum computing in the simulation of active-space electronic wavefunctions of substituted aromatic heterocycles, and outline challenges to be overcome in elucidating the optical properties of organic molecules with hybrid quantum-classical algorithms.

DOI
10.48550/arxiv.2309.09868

Related papers

Quantum computation of π → π* and n → π* excited states of aromatic heterocycles

Maria A. Castellanos, Mário Motta, Julia E. Rice

The computation of excited electronic states is an important application for quantum computers. In this work, we simulate the excited state spectra of four aromatic heterocycles on IBM superconducting quantum computers, focussing on active spaces of π→π∗ and n→π∗ excitations. We approximate the ground state with the entanglement forging method, a qubit reduction technique that maps a spatial orbital to a single qubit, rather than two qubits. We then determine excited states using the quantum subspace expansion method. We showcase these algorithms on quantum hardware using up to 8 qubits and employing readout and gate error mitigation techniques. Our results demonstrate a successful application of quantum computing in the simulation of active-space electronic wavefunctions of substituted aromatic heterocycles, and outline challenges to be overcome in elucidating the optical properties of organic molecules with hybrid quantum-classical algorithms.

Molecular Physics•Nov 15, 2023•5 citations

Computation of Molecular Spectra on a Quantum Processor with an Error-Resilient Algorithm

James Colless, Vinay Ramasesh, Dar Dahlen +6 more

Harnessing the full power of nascent quantum processors requires the efficient management of a limited number of quantum bits with finite coherent lifetimes.Hybrid algorithms, such as the variational quantum eigensolver (VQE), leverage classical resources to reduce the required number of quantum gates.Experimental demonstrations of VQE have resulted in calculation of Hamiltonian ground states, and a new theoretical approach based on a quantum subspace expansion (QSE) has outlined a procedure for determining excited states that are central to dynamical processes.We use a superconducting-qubit-based processor to apply the QSE approach to the H 2 molecule, extracting both ground and excited states without the need for auxiliary qubits or additional minimization.Further, we show that this extended protocol can mitigate the effects of incoherent errors, potentially enabling larger-scale quantum simulations without the need for complex error-correction techniques.

arXiv:1707.06408•Physical Review X•Feb 12, 2018•458 citations

Quantum Computer Simulates Excited States of Molecule

Sukin Sim, Jonathan Romero, Peter D. Johnson +1 more

Harnessing the full power of nascent quantum processors requires the efficient management of a limited number of quantum bits with finite coherent lifetimes.Hybrid algorithms, such as the variational quantum eigensolver (VQE), leverage classical resources to reduce the required number of quantum gates.Experimental demonstrations of VQE have resulted in calculation of Hamiltonian ground states, and a new theoretical approach based on a quantum subspace expansion (QSE) has outlined a procedure for determining excited states that are central to dynamical processes.We use a superconducting-qubit-based processor to apply the QSE approach to the H 2 molecule, extracting both ground and excited states without the need for auxiliary qubits or additional minimization.Further, we show that this extended protocol can mitigate the effects of incoherent errors, potentially enabling larger-scale quantum simulations without the need for complex error-correction techniques.

Physics•Feb 12, 2018•6 citations

Quantum-centric computation of molecular excited states with extended sample-based quantum diagonalization

Stefano Barison, Javier Robledo Moreno, Mário Motta

Abstract The simulation of molecular electronic structure is an important application of quantum devices. Recently, it has been shown that quantum devices can be effectively combined with classical supercomputing centers in the context of the sample-based quantum diagonalization (SQD) algorithm. This allowed the largest electronic structure quantum simulation to date (77 qubits) and opened near-term devices to practical use cases in chemistry toward the hundred-qubit mark. However, the description of many important physical and chemical properties of those systems, such as photo-absorption/-emission, requires a treatment that goes beyond the ground state alone. In this work, we extend the SQD algorithm to determine low-lying molecular excited states. The extended-SQD method improves over the original SQD method in accuracy, at the cost of an additional computational step. It also improves over quantum subspace expansion based on single and double electronic excitations, a widespread approach to excited states on pre-fault-tolerant quantum devices, in both accuracy and efficiency. We employ the extended SQD method to compute the first singlet (S 1) and triplet (T 1) excited states of the nitrogen molecule with a correlation-consistent basis set, and the ground- and excited-state properties of the [2Fe-2S] cluster.

arXiv:2411.00468•Quantum Science and Technology•Feb 18, 2025•34 citations

Quantum Computing for Electronic Circular Dichroism Spectrum Prediction of Chiral Molecules

Amandeep Singh Bhatia, Sabre Kais

Electronic circular dichroism (ECD) spectroscopy captures the chiroptical response of molecules, enabling absolute configuration assignment that is vital for enantioselective synthesis and drug design. The practical use of ECD spectra in predictive modeling remains restricted, as existing approaches offer limited confidence for chiral discrimination. By contrast, theoretical ECD calculations demand substantial computational effort rooted in electronic structure theory, which constrains their scalability to larger chemically diverse molecules. These limitations underscore the need for computational approaches that retain first principles physical rigor while enabling efficient and scalable prediction. Motivated by recent advances in quantum algorithms for chemistry, we introduce a variational quantum framework combined with the quantum equation of motion formalism to compute molecular properties and predict ECD spectra, implemented within a multi GPU or QPU accelerated hybrid quantum/classical workflow. We demonstrate its efficient applicability on 12 clinically relevant chiral drug molecules accessing expanded active spaces. The proposed framework is assessed by comparison with established classical wavefunction based methods, employing Coupled Cluster Singles and Doubles (CCSD) for ground-state energy benchmarks and Complete Active Space Configuration Interaction (CASCI) as the reference method for excited state energies and chiroptical properties within the same active orbital space. Notably, the quantum computed ECD spectra, obtained from chemically relevant active spaces mapped onto quantum circuits of approximately 20 to 24 qubits, exhibit near quantitative agreement with classical reference calculations, accurately reproducing spectral line shapes, Cotton effect signs, and relative peak intensities.

quant-pharXiv:2602.03710•Feb 4, 2026•0 citations

Workflow for practical quantum chemical calculations with a quantum phase estimation algorithm: electronic ground and π–π* excited states of benzene and its derivatives

Y. Ino, Misaki Yonekawa, Hideto Yuzawa +2 more

Quantum computers are expected to perform full-configuration interaction calculations with less computational resources compared to classical ones, thanks to the use of quantum phase estimation (QPE) algorithms. However, only a limited number of QPE-based quantum chemical calculations have been reported even for numerical simulations on a classical computer, and the practical workflow for the QPE computation has not yet been established. In this paper, we report the QPE simulations of the electronic ground and the π-π* excited singlet state of benzene and its chloro- and nitro-derivatives as the representative industrially important systems, with the aid of GPGPU acceleration of quantum circuit simulations. We adopted the pseudo-natural orbitals obtained from the MP2 calculation as the basis for the wave function expansion, the CISD calculation within the active space to find the main electronic configurations to be included in the input wave function of the excited state, and the technique to reduce the truncation error of the calculated total energies. The proposed computational workflow is easily applicable to other molecules and can be a standard approach for performing QPE-based quantum chemical calculations of practical molecules.

arXiv:2312.16375•Physical Chemistry Chemical Physics•Jan 1, 2024•10 citations
Quantum computation of π→π∗π\to π^*π→π∗ and n→π∗n \to π^*n→π∗ excited states of aromatic heterocycles
The computation of excited electronic states is an important application for quantum computers. In this work, we simulate the excited state spectra of four aromatic heterocycles on IBM superconducting quantum computers, focusing on active spaces of π→π∗π\to π^*π→π∗ and n→π∗n \to π^*n→π∗ excitations. We approximate the ground state with the entanglement forging method, a qubit reduction technique that maps a spatial orbital to a single qubit, rather than two qubits. We then determine excited states using the quantum subspace expansion method. We showcase these algorithms on quantum hardware using up to 8 qubits and employing readout and gate error mitigation techniques. Our results demonstrate a successful application of quantum computing in the simulation of active-space electronic wavefunctions of substituted aromatic heterocycles, and outline challenges to be overcome in elucidating the optical properties of organic molecules with hybrid quantum-classical algorithms.
The computation of excited electronic states is an important application for quantum computers. In this work, we simulate the excited state spectra of four aromatic heterocycles on IBM superconducting quantum computers, focussing on active spaces of π→π∗ and n→π∗ excitations. We approximate the ground state with the entanglement forging method, a qubit reduction technique that maps a spatial orbital to a single qubit, rather than two qubits. We then determine excited states using the quantum subspace expansion method. We showcase these algorithms on quantum hardware using up to 8 qubits and employing readout and gate error mitigation techniques. Our results demonstrate a successful application of quantum computing in the simulation of active-space electronic wavefunctions of substituted aromatic heterocycles, and outline challenges to be overcome in elucidating the optical properties of organic molecules with hybrid quantum-classical algorithms.
Harnessing the full power of nascent quantum processors requires the efficient management of a limited number of quantum bits with finite coherent lifetimes.Hybrid algorithms, such as the variational quantum eigensolver (VQE), leverage classical resources to reduce the required number of quantum gates.Experimental demonstrations of VQE have resulted in calculation of Hamiltonian ground states, and a new theoretical approach based on a quantum subspace expansion (QSE) has outlined a procedure for determining excited states that are central to dynamical processes.We use a superconducting-qubit-based processor to apply the QSE approach to the H 2 molecule, extracting both ground and excited states without the need for auxiliary qubits or additional minimization.Further, we show that this extended protocol can mitigate the effects of incoherent errors, potentially enabling larger-scale quantum simulations without the need for complex error-correction techniques.
Harnessing the full power of nascent quantum processors requires the efficient management of a limited number of quantum bits with finite coherent lifetimes.Hybrid algorithms, such as the variational quantum eigensolver (VQE), leverage classical resources to reduce the required number of quantum gates.Experimental demonstrations of VQE have resulted in calculation of Hamiltonian ground states, and a new theoretical approach based on a quantum subspace expansion (QSE) has outlined a procedure for determining excited states that are central to dynamical processes.We use a superconducting-qubit-based processor to apply the QSE approach to the H 2 molecule, extracting both ground and excited states without the need for auxiliary qubits or additional minimization.Further, we show that this extended protocol can mitigate the effects of incoherent errors, potentially enabling larger-scale quantum simulations without the need for complex error-correction techniques.
Abstract The simulation of molecular electronic structure is an important application of quantum devices. Recently, it has been shown that quantum devices can be effectively combined with classical supercomputing centers in the context of the sample-based quantum diagonalization (SQD) algorithm. This allowed the largest electronic structure quantum simulation to date (77 qubits) and opened near-term devices to practical use cases in chemistry toward the hundred-qubit mark. However, the description of many important physical and chemical properties of those systems, such as photo-absorption/-emission, requires a treatment that goes beyond the ground state alone. In this work, we extend the SQD algorithm to determine low-lying molecular excited states. The extended-SQD method improves over the original SQD method in accuracy, at the cost of an additional computational step. It also improves over quantum subspace expansion based on single and double electronic excitations, a widespread approach to excited states on pre-fault-tolerant quantum devices, in both accuracy and efficiency. We employ the extended SQD method to compute the first singlet (S 1) and triplet (T 1) excited states of the nitrogen molecule with a correlation-consistent basis set, and the ground- and excited-state properties of the [2Fe-2S] cluster.
Electronic circular dichroism (ECD) spectroscopy captures the chiroptical response of molecules, enabling absolute configuration assignment that is vital for enantioselective synthesis and drug design. The practical use of ECD spectra in predictive modeling remains restricted, as existing approaches offer limited confidence for chiral discrimination. By contrast, theoretical ECD calculations demand substantial computational effort rooted in electronic structure theory, which constrains their scalability to larger chemically diverse molecules. These limitations underscore the need for computational approaches that retain first principles physical rigor while enabling efficient and scalable prediction. Motivated by recent advances in quantum algorithms for chemistry, we introduce a variational quantum framework combined with the quantum equation of motion formalism to compute molecular properties and predict ECD spectra, implemented within a multi GPU or QPU accelerated hybrid quantum/classical workflow. We demonstrate its efficient applicability on 12 clinically relevant chiral drug molecules accessing expanded active spaces. The proposed framework is assessed by comparison with established classical wavefunction based methods, employing Coupled Cluster Singles and Doubles (CCSD) for ground-state energy benchmarks and Complete Active Space Configuration Interaction (CASCI) as the reference method for excited state energies and chiroptical properties within the same active orbital space. Notably, the quantum computed ECD spectra, obtained from chemically relevant active spaces mapped onto quantum circuits of approximately 20 to 24 qubits, exhibit near quantitative agreement with classical reference calculations, accurately reproducing spectral line shapes, Cotton effect signs, and relative peak intensities.
Quantum computers are expected to perform full-configuration interaction calculations with less computational resources compared to classical ones, thanks to the use of quantum phase estimation (QPE) algorithms. However, only a limited number of QPE-based quantum chemical calculations have been reported even for numerical simulations on a classical computer, and the practical workflow for the QPE computation has not yet been established. In this paper, we report the QPE simulations of the electronic ground and the π-π* excited singlet state of benzene and its chloro- and nitro-derivatives as the representative industrially important systems, with the aid of GPGPU acceleration of quantum circuit simulations. We adopted the pseudo-natural orbitals obtained from the MP2 calculation as the basis for the wave function expansion, the CISD calculation within the active space to find the main electronic configurations to be included in the input wave function of the excited state, and the technique to reduce the truncation error of the calculated total energies. The proposed computational workflow is easily applicable to other molecules and can be a standard approach for performing QPE-based quantum chemical calculations of practical molecules.