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Rovibrational energy levels of H2O by quantum computing
Erik Lötstedt1,2,3, Tamás Szidarovszky4
1RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), Wako, Saitama 351-0198, Japan.
The Journal of Chemical Physics
|July 13, 2026
Summary
Researchers used a trapped-ion quantum computer to calculate water (H2O) energy levels. This quantum approach accurately determined molecular vibrations and rotations, paving the way for advanced chemical simulations.
Area of Science:
- Quantum computing applications in molecular physics.
- Computational chemistry and spectroscopy.
- Development of quantum algorithms for scientific problems.
Background:
- Accurate calculation of molecular energy levels is crucial for understanding chemical reactions and molecular properties.
- Traditional computational methods face challenges with complex molecular systems.
- Quantum computing offers a potential new paradigm for solving intractable problems in quantum chemistry.
Purpose of the Study:
- To calculate the rovibrational energy levels of water (H2O) using a trapped-ion quantum computer.
- To adapt Watson's Hamiltonian into a qubit form suitable for quantum computation.
- To explore the capabilities of quantum algorithms for molecular energy level determination.
Main Methods:
- Derivation of the qubit form of Watson's Hamiltonian, incorporating rovibrational coupling.
- Application of a quantum-selected configuration-interaction method.
- Generation of correlated rovibrational wave functions via quantum computer time evolution.
- Basis set selection through probability distribution sampling.
- Construction and diagonalization of the Hamiltonian matrix on a classical computer.
Main Results:
- Successful calculation of rovibrational energy levels for H2O using a quantum computer.
- Demonstration of a quantum-selected configuration-interaction approach for molecular calculations.
- Achieved accuracy of a few hc cm⁻¹ for low-lying energy levels.
Conclusions:
- Trapped-ion quantum computers can accurately compute molecular rovibrational energy levels.
- The developed quantum algorithm shows promise for future applications in molecular spectroscopy and quantum chemistry.
- This work highlights the potential of quantum computation to advance our understanding of molecular systems.
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