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arXiv:2603.05795 · The Journal of Chemical Physics

Rovibrational energy levels of H$_2$O by quantum computing

Erik Lötstedt, Tamás Szidarovszky

quant-phSubmitted Mar 6, 2026• Announced Mar 9, 2026• 1 citation• Revised Jul 14, 2026 (v2)
v1 · Mar 6, 2026v2 · Jul 14, 2026
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Abstract

We calculate rovibrational energy levels of H$_2$O using a trapped-ion quantum computer. We first derive the qubit form of Watson's Hamiltonian, including the rovibrational coupling terms. In a second step, we employ a variant of the quantum-selected configuration-interaction method to calculate rovibrational energy levels. A truncated form of the qubit Hamiltonian is used to generate correlated rovibrational wave functions on the quantum computer by time evolution, and a basis set is selected by sampling from the measured probability distribution. The rovibrational energy levels are obtained by constructing a Hamiltonian matrix using the selected basis set, and diagonalizing the matrix using a classical computer. We show that an accuracy of a few $hc$ cm$^{-1}$ can be achieved for low-lying rovibrational energy levels.

Journal reference
J. Chem. Phys. 165, 024118 (2026)
DOI
10.1063/5.0333947
Comments
Version 2 corresponds to the published version

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