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Key Chemistry Question Answered, No Quantum Computer Required
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chemistry
Key Chemistry Question Answered, No Quantum Computer Required
By
Kevin Hartnett
May 29, 2026
Do we need quantum computers to fully understand complex chemical reactions? A new result, decades in the making, shows the surprising power of ordinary “classical” machines.
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Nash Weerasekera for Quanta Magazine
Introduction
By Kevin Hartnett
Contributing Writer
May 29, 2026
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chemistry
computer science
quantum computing
quantum physics
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What Garnet Chan cares most about is basic science. He entered chemistry decades ago to understand some of the most consequential biochemical processes on Earth.
But since then, he’s become a central figure in a different arena: the debate over whether quantum computers will have a decisive advantage over ordinary “classical” ones. Over the past decade, many quantum computing researchers have identified the very reactions Chan studies as an area in which quantum computers should excel. Chan, however, has long doubted that powerful quantum computers — which are still years away — will be necessary.
“My main interest is in solving chemical problems. If classical computers are the right tool to do it, we should,” he said. While he believes quantum computers will eventually play an important role in the field, “I don’t see why we should wait for a fault-tolerant quantum computer to be built.”
Now he has a result that strengthens his case.
In early January, Chan and five other quantum chemists based out of the California Institute of Technology reached a key milestone in understanding the enzyme nitrogenase, which converts atmospheric nitrogen into ammonia and makes life on our planet possible. It was a major triumph for theoretical chemists, the outcome of decades of effort.
But for years, nitrogenase had also served as a proof-of-concept target in the realm of quantum computing. To understand the enzyme, researchers must follow the behavior of many electrons that are all linked together via quantum entanglement. The number of possible configurations grows explosively large. Researchers hypothesized that they would likely only be able to decipher the system via a machine that could manipulate quantum states.
But Chan and his colleagues used purely classical methods. That makes their result a pivotal statement not only about the chemistry that supports life, but also about whether quantum computers are needed to understand it.
“I think it’s important to clarify that this is not an impossible task where you have to first build a quantum computer to say anything about the problem,” Chan said.
While Garnet Chan is excited for the day when quantum computers will help solve important problems in chemistry, he sees no need to wait: Contrary to popular belief, he argues, quantum computers aren’t needed to answer some of the field’s biggest questions.
Jerry Camarillo Photography
Not everyone agrees. Some researchers cite the many years it took to obtain the result classically. Even if one chemistry problem has ultimately proved tractable with classical methods, they say, quantum computers are still needed to make these kinds of discoveries at scale.
“If we pick any optimization problem and you put 20 years into it, you can figure out that one system,” said James Whitfield, a quantum computing theorist at Dartmouth College. “But whether that solution is transferable? Questions like that won’t be answered by solving one instance of one molecular system.”
Solving this particular problem about nitrogenase may not settle the debate over quantum computers just yet, but each step toward understanding the enzyme’s full chemistry makes the debate less hypothetical.
Nature’s Ammonia Factory
Alongside photosynthesis, nitrogen fixation is one of the most essential chemical processes for life on Earth. Nitrogenase is what makes it possible.
Before nitrogenase evolved, living things were limited by the amount of nitrogen available to be incorporated into organic matter. It was an ironic obstacle, given that the planet was in fact suffused with nitrogen: The element accounts for about 80% of the atmosphere. But atmospheric nitrogen exists as the diatomic molecule N2, which is inert and therefore unusable in biological processes. Only rare high-energy events could break the...