Quantum computing breakthrough brings scientists closer to predicting chemical reactions

Physicist Cornelius Hempel has led a breakthrough that brings scientists closer to being able to create designer chemical reactions.

Dr Cornelius Hempel: ‘It’s important that we pursue many different technologies in parallel’. Picture: Virginia Frey

University of Sydney physicist Cornelius Hempel has led a breakthrough in quantum computing that brings scientists closer to being able to create designer chemical reactions.

The ability to predict what reactions will occur between various types of atoms and molecules is a holy grail in chemistry and, if achieved, will transform many areas of science and technology including industrial chemistry, materials science, medicine and pharmaceuticals.

In a paper published this week in the top journal Physical Review X, Dr Hempel and his co-authors — Rainer Blatt and Alan Aspuru-Guzik — revealed they successfully ran algorithms on a simple quantum computer to calculate the energy levels of the atomic bonds in molecules of hydrogen and lithium hydride.

The work, done by Dr Hempel’s former research group at the Institute for Quantum Optics and Quantum Information in Innsbruck, Austria, is a first.

“It’s the first time that an ion trap (quantum computer) has actually simulated molecules of multiple atoms and elements,” said Dr Hempel, who joined the University of Sydney in 2016.

Similar problems have been done on superconducting quantum computers.

Dr Hempel said there was value in doing the same problems on different types of systems.

“If we get the same answer then there’s a high chance that answer is probably correct. It’s important that we pursue many different technologies in parallel,” he said.

Currently even relatively simple chemical reactions are difficult, if not impossible, to predict accurately with classical computers because of the extremely complex mathematics required to use quantum mechanics to find energy levels of atoms and molecules. However, quantum computers offer a short cut to solving quantum problems by using analog methods — essentially creating a model of the problem instead of having to plough through an enormous quantity of mathematical calculations.

In their method, Dr Hempel and his colleagues paired their simple quantum computer with a classical computer, asking the quantum machine to aid the conventional one.

They chose to use simple molecules so the answers could be independently checked. Their work used only four qubits (or quantum logic gates), which is not nearly powerful enough to model complex chemical reactions.

Dr Hempel said it was important because his team could search for errors and plan improvements. It serves as a model for scaling up, if and when far more powerful quantum computers are built that can calculate the energy levels of complex molecules.

This would help scientists to create their own chemical reactions for specific purposes — for example, designing pharmaceutical drugs or making the energy-hungry process of producing fertiliser more efficient.