Bayesian quantum algorithm directly calculates atom and molecule energy difference

Researchers from the Graduate School of Science at Osaka City University developed a quantum algorithm that comprehends the electronic states of atomic or molecular systems by directly calculating the energy difference in their relevant states.  Their work was just published in the journal Physical Chemistry Chemical Physics,

The algorithm is implemented as a Bayesian phase different estimation and rather than focusing on the difference in total energies calculated from the pre- and post-phase evolution it follows the evolution of the energy difference itself.

According to research lead Kenji Sugisaki, “Almost all chemistry problems discuss the energy difference, not the total energy of the molecule itself. Also, molecules with heavy atoms that appear at the lower part of the periodic table have large total energies, but the size of the energy difference discussed in chemistry, such as electronic excitation states and ionization energies, does not depend much on the size of the molecule.”

This was the basis of the research, implementing a quantum algorithm that directly calculates energy differences instead of total energies, so that scalable or practical quantum computers enable us to carry out actual chemical research and materials development.

Previously, this research group developed a quantum algorithm that directly calculates the energy difference between electronic states (spin states) with different spin quantum numbers (K. Sugisaki, K. Toyota, K. Sato, D. Shiomi, T. Takui, Chem. Sci. 2021, 12, 2121–2132.). This algorithm, however, needs more qubits than the conventional QPE and cannot be applied to the energy difference calculation between the electronic states with equal spin quantum numbers, which is important for the spectral assignment of UV-visible absorption spectra. The BPDE algorithm developed in the study overcomes these issues, making it a highly versatile quantum algorithm. For more information on the research and results, visit:

Original Release: Eureka Alert

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