Quantum device used to slow chemical reaction 100 billion times

The research team observed an interference pattern of a single atom due to a "conical intersection," a common geometric structure in chemistry. These play a crucial role in rapid photochemical processes, such as light harvesting in human vision and photosynthesis. Chemists have attempted to observe geometric processes in chemical dynamics since the 1950s, but direct observation is not feasible due to the rapid timescales involved.

A team of quantum researchers from the School of Physics and the School of Chemistry at the University of Sydney have developed a novel approach to solving a complex problem using a trapped-ion quantum computer. This innovative method allowed them to effectively map the problem onto a relatively small quantum device and slow the process by an impressive factor of 100 billion.

"In nature, the whole process is over within femtoseconds," said Olaya Agudelo from the School of Chemistry. "That's a billionth of a millionth—or one quadrillionth—of a second," she added. "Using our quantum computer, we built a system that allowed us to slow down the chemical dynamics from femtoseconds to milliseconds. This allowed us to make meaningful observations and measurements," they said. "This has never been done before," they concluded.

Joint lead author Dr. Christophe Valahu from the School of Physics said, "Until now, we have been unable to directly observe the dynamics of 'geometric phase'; it happens too fast to probe experimentally... "Using quantum technologies, we have addressed this problem."

"Our experiment wasn't a digital approximation of the process—this was a direct analog observation of the quantum dynamics unfolding at a speed we could observe," he added. In photochemical reactions, such as photosynthesis, by which plants obtain energy from the sun, molecules rapidly transfer energy, creating exchange regions called conical intersections. This study revealed the tell-tale hallmarks associated with conical intersections in photochemistry by slowing down the dynamics in the quantum computer.

"This exciting result will help us better understand ultrafast dynamics—how molecules change at the fastest timescales," explained co-author and research team leader, Associate Professor Ivan Kassal from the School of Chemistry and the University of Sydney Nano Institute. "It is tremendous that at the University of Sydney, we have access to the country's best programmable quantum computer to conduct these experiments," he added.

A fantastic achievement

The experiment was conducted using the quantum computer in the Quantum Control Laboratory, founded by Professor Michael Biercuk. Dr. Ting Rei Tan led the effort. "This is a fantastic collaboration between chemistry theorists and experimental quantum physicists. We are using a new approach in physics to tackle a long-standing problem in chemistry," added Tan, a co-author of the study.

You can view the study for yourself in the journal Nature Chemistry.

Study abstract:

Conical intersections are ubiquitous in chemistry and physics, often governing processes such as light harvesting, vision, photocatalysis and chemical reactivity. They act as funnels between electronic states of molecules, allowing rapid and efficient relaxation during chemical dynamics. In addition, when a reaction path encircles a conical intersection, the molecular wavefunction experiences a geometric phase, which can affect the outcome of the reaction through quantum-mechanical interference. Past experiments have measured indirect signatures of geometric phases in scattering patterns and spectroscopic observables, but there has been no direct observation of the underlying wavepacket interference. Here we experimentally observe geometric-phase interference in the dynamics of a wavepacket travelling around an engineered conical intersection in a programmable trapped-ion quantum simulator. To achieve this, we develop a technique to reconstruct the two-dimensional wavepacket densities of a trapped ion. Experiments agree with the theoretical model, demonstrating the ability of analogue quantum simulators—such as those realized using trapped ions—to accurately describe nuclear quantum effects.