Quantum computing provides new insight into photochemical processes

Quantum computing has provided new insights into fundamental aspects of photochemical reactions that have previously proven difficult to study. These findings could improve scientists’ understanding of light-driven processes such as photosynthesis, smog formation and ozone depletion.

Photochemistry occurs when atomic nuclei and their electrons have different configurations after absorbing a photon. Some of these reactions are guided by a quantum phenomenon called cone intersection, where potential energy surfaces describe a molecule in the ground state and in the convergent excited states. In these situations, quantum mechanical interference can prevent certain molecular transformations from taking place – a constraint known as geometric phase. This limits the path of the reaction and affects the result of the reaction. The geometric phase has been known since the 1950s, but due to its femtosecond period it has never been directly observed in a molecular system.

Now, two research groups working independently have shown how geometric phase can be measured using quantum simulations.

“This phase is difficult to see in real molecules because it takes place far from the ground state and requires a clean quantum state with little thermal noise,” says quantum systems researcher Kenneth Brown from Duke University in the US. North Carolina, USA said.

“We built a quantum system that has some properties of the system that we want to study,” Brown said. The design of the quantum simulator allows the Duke team to measure the effect “at a much more readable timescale,” Brown said.

The researchers used a laser to direct a chain of five trapped ytterbium ions in a way that mimics the quantum behavior of atoms at a conical intersection. Since the quantum dynamics of the trapped ions are much slower than the quantum dynamics of the molecule, the team was able to directly measure how the geometrical phase affects the spatial distribution of the wavefunction of the ions. ions.

“Our experiment is one of the earliest demonstrations of how we can perform electron-oscillatory coupling of trapped ions,” Brown said. He notes that understanding phase geometry could give chemists “another way to control” the products produced in multi-product reactions.

The Duke team’s findings were published alongside similar work led by researchers at the University of Sydney, Australia. The team led by Ivan Kassal used a similar quantum simulator based on a single trapped ytterbium ion.

‘One of the most important things here is that we can observe, in real time, how fast the geometric phase interference in this system acts as [a] molecular systems,” said Vanessa Agudelo, a doctoral student in Kassal’s lab who worked on the project.

Quantum computers allow them to slow down the chemical dynamics of the system they are studying from femtoseconds down to milliseconds, allowing meaningful observations.

“Here you have a realistic video of a single atom splitting in half, … intersecting with itself radially as it crosses over to the other side of the conical intersection,” explains Kassal. ‘This is a simulation of an incoming photon and how the molecule interacts over a femtosecond period.’

‘That’s especially important in things like atmospheric chemistry – why does fog form? How is the ozone layer formed? Or how was it destroyed?’ he added.

Although the technical approach taken by the two groups was different, their results were consistent. Kassal notes that this work highlights how quantum computing can help solve complex chemical problems. “The goal of using quantum computers for chemistry is to be able to simulate any kind of chemical process… like discovering drugs or discovering better materials,” he said.