HomeSciencePhysicsQuantum algorithms save time in the calculation of electron dynamics

Quantum algorithms save time in the calculation of electron dynamics

With the calculations, the electron densities and the changes after excitation can be determined with a high spatial and temporal resolution. Here, the example of the lithium hydride molecule shows the electron density shift from cyanide (red) to lithium (green) during a laser pulse. Credits: F. Langkabel / HZB

Researchers have investigated the ability of known quantum computing algorithms for fault-tolerant quantum computing to simulate the laser-driven electron dynamics of small molecule excitation and ionization processes. Their research has been published in the Journal of chemical theory and computation.

“This quantum computer algorithms were originally developed in a completely different context. We used them here for the first time to calculate the electron density of moleculesin particular their dynamic evolution after excitation by a light pulse”, says Annika Bande, who leads a group theoretical chemistry at Helmholtz Association of German Research Centers (HZB). Bande and Fabian Langkabel, who is doing her PhD with her, show how well this works in their research.

“We developed an algorithm for a fictitious, completely error-free quantum computer and ran it on a classical server that simulated a ten-qubit quantum computer,” says Langkabel. The scientists limited their study to smaller molecules in order to perform the calculations without a real quantum computer and to compare them with conventional calculations.

The quantum algorithms yielded the expected results. Unlike conventional calculations; however, the quantum algorithms are also suitable for calculating considerably larger molecules with future quantum computers.

“That has to do with the calculation times, which increase with the number of atoms that make up the molecule,” says Langkabel. While the computation time multiplies with each additional atom for conventional methods, this is not the case for quantum algorithmsmaking them much faster.

Photocatalysis, light reception and more

The study thus shows a new way to pre-calculate electron densities and their “response” to excitations with light, with very high spatial and temporary resolution. This makes it possible, for example, to simulate and understand ultrafast decay processes, which are also crucial in quantum computers made of so-called quantum dots.

In addition, predictions are possible about the physical or chemical behavior of molecules, for example during the absorption of light and the subsequent transfer of electrical charges.

This could facilitate the development of photocatalysts for the production of green hydrogen using sunlight or help to understand processes in the light-sensitive receptor molecules in the eye.

More information:
Fabian Langkabel et al, Quantum-Compute Algorithm for Exact Laser-Driven Electron Dynamics in Molecules, Journal of chemical theory and computation (2022). DOI: 10.1021/acs.jctc.2c00878

Quote: Quantum Algorithms Save Time Computing Electron Dynamics (2022, Nov. 23) Retrieved Nov. 23, 2022 from

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