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arXiv · 2509.04727

Qumode-Based Variational Quantum Eigensolver for Molecular Excited States

Rishab Dutta·Cameron Cianci·Alexander V. Soudackov·Yuchen Wang·Chuzhi Xu·David A. Mazziotti·Lea F. Santos·Victor S. Batista
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Abstract

We introduce the Qumode Subspace Variational Quantum Eigensolver (QSS-VQE), a hybrid quantum-classical algorithm for computing molecular excited states using the Fock basis of bosonic qumodes in circuit quantum electrodynamics (cQED) devices. This approach harnesses the native universal gate sets of qubit-qumode architectures to construct highly expressive variational ansatze, offering potential advantages over conventional qubit-based methods. In QSS-VQE, the electronic structure Hamiltonian is first mapped to a qubit representation and subsequently embedded into the Fock space of bosonic qumodes, enabling efficient state preparation and reduced quantum resource requirements. We demonstrate the performance of QSS-VQE through simulations of molecular excited states, including dihydrogen and a conical intersection in cytosine. Additionally, we explore a bosonic model Hamiltonian to assess the expressivity of qumode gates, identifying regimes where qumode-based implementations outperform purely qubit-based approaches. These results highlight the promise of leveraging bosonic degrees of freedom for enhanced quantum simulation of complex molecular systems.

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Rishab Dutta, Cameron Cianci, Alexander V. Soudackov, Yuchen Wang, Chuzhi Xu, David A. Mazziotti, Lea F. Santos, Victor S. Batista. 2025-09-05. Qumode-Based Variational Quantum Eigensolver for Molecular Excited States. https://doi.org/10.1021/acs.jctc.5c01494

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