Evrim Yazgin
Cosmos science journalist
Researchers have used a quantum computer to simulate dynamic chemical processes of real molecules for the first time.
The milestone is at the cusp of what modern classical supercomputers cannot achieve, pointing to the advances in chemistry, materials science and medicine that will come with quantum computing.
Quantum computers have previously been used to calculate the static properties of molecules. But the new study, published in the Journal of the American Chemical Society, shows a chemical process in action over time simulated on a quantum device for the first time.
Of molecules and light
“Our new approach allows us to simulate the full dynamics of an interaction between light and chemical bonds,” says senior author Ivan Kassal from Australia’s University of Sydney (USyd). “It’s like understanding the position and energy of the mountain hiker at any time point of their journey through the mountains.”
The quantum computer at the university’s Nano Institute simulates the interaction of photons, light particles, with molecules allene, butatriene and pyrazine. The process involves the chemical bonds between atoms in the molecules absorbing a photon, vibrating and seeing electrons within the bonds transitioning to higher energy states.
All of this occurs in a matter of femtoseconds in reality – 1 femtosecond is a million billion times smaller than a second.
But the simulation allows researchers to slow this down by 100 billion times to watch the interaction in the much more reasonable timeframe of milliseconds.
Each molecule tested exhibits a different kind of photochemistry. They are small molecules, manageable with a quantum simulator in progress, which still showcase different ways that light drives chemistry in nature.
Photon-induced chemical processes are critical to life, renewable energy and medicine. Such processes include photosynthesis, DNA damage by UV, sunscreen design, solar cell production, photodynamic therapies and cancer research.
“In all these cases, the ultrafast photo-induced dynamics are poorly understood,” says author Tingrei Tan also from USyd. “Having accurate simulation tools will accelerate the discovery of new materials, drugs, or other photoactive molecules.”
1-ion simulator
The team’s device is a testament to the potential power of quantum computing.
It is not a digital quantum computer that can be programmed to perform a number of different functions. It is an analogue quantum simulator which is specifically designed to tackle a known problem. Cosmos has done a deep dive into the difference between digital and analogue quantum computers in a magazine feature, “Quantum simulations”.
Kassal explains that this analogue approach is the key to the device’s efficiency.
“Performing the same simulation using a more conventional approach in quantum computing would require 11 perfect qubits and 300,000 flawless entangling gates. Our approach is about a million times more resource-efficient, enabling complex chemical dynamics to be studied with far fewer resources than previously thought possible,” he says.
The USyd team used a single trapped ion to simulate the chemical process.
“We used a single ytterbium ion as the heart of our quantum simulator. It’s held in place with electromagnetic fields inside a vacuum chamber and manipulated using lasers. Ytterbium is a favourite in quantum computing because it’s stable, controllable, and its internal structure allows us to encode quantum information with great precision,” Kassal tells Cosmos in an email.
“In our case, we used the ion’s electronic states to mimic a molecule’s electronic structure, and its vibrations to represent nuclear motion,” he adds.
A step toward “quantum supremacy”
Kassal says the results match existing understanding of the molecules.
“For each molecule, we were able to reproduce the expected dynamics – the probability of being in one electronic state or another, how that evolves over time, and how the wavepacket (the quantum analogue of a moving particle) behaves,” he explains.
Developments in quantum computing such as this are a further indication that scientists and engineers are on the brink of performing calculations on quantum devices which cannot be done on even the most powerful classical supercomputers.
“It is possible to simulate the interactions for these particular molecules using classical supercomputers. But more complex molecules will beyond their capabilities. Quantum tech will be able to simulate such complexity that is beyond all classical capability,” says Tan.
“This is a proof of concept that quantum simulators can do real chemistry,” Kassal adds. “Until now, most quantum simulations were either idealised or limited to static molecular properties. We’ve shown that you can now simulate real-time chemical dynamics using existing quantum hardware.
“We believe that with a modest increase in scale – to perhaps 20 or 30 ions – quantum simulations could tackle chemical systems that are completely out of reach for any classical computer – things like large molecules in solution, photochemical pathways in proteins, or next-generation materials for energy conversion.”
