Quantum algorithms save time in calculating electron dynamics

Researchers investigated the ability of known quantum computing algorithms for fault-tolerant quantum computing to simulate the laser-driven electronic dynamics of excitation and ionization processes in small molecules. Their research is published in the Journal of Chemical Theory and Computation.

“These quantum computer algorithms were originally developed in a completely different context. We used them here for the first time to calculate the electronic densities of molecules, in particular their dynamic evolution after excitation by a light pulse”, explains Annika Bande, who leads a group in theoretical chemistry at the Helmholtz Association of German Research Centers (HZB). Bande and Fabian Langkabel, who is doing her doctorate with her, show in the study how well it works.

“We developed an algorithm for a fictional, completely error-free quantum computer and ran it on a classical server simulating a ten-qubit quantum computer,” says Langkabel. The scientists limited their study to smaller molecules so that they could perform the calculations without a real quantum computer and compare them to classical calculations.

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

“It has to do with computation times. They increase with the number of atoms that make up the molecule,” says Langkabel. While computation time multiplies with each additional atom for classical methods, this is not the case for quantum algorithms, making them much faster.

Photocatalysis, light reception and more

The study thus shows a new way of calculating the densities of electrons and their “response” to light excitations in advance, with a very high spatial and temporal 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 about the physical or chemical behavior of molecules are possible, 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 with sunlight or help understand processes in light-sensitive receptor molecules in the eye.