Science and the IT industry have high hopes for quantum computing, but descriptions of possible applications tend to be vague. Researchers at ETH Zurich have now come up with a concrete example that demonstrates what quantum computers will actually be able to achieve in the future.
Specialists expect nothing less than a technological revolution from quantum computers, which they hope will soon allow them to solve problems that are currently too complex for classical supercomputers. Commonly discussed areas of application include data encryption and decryption, as well as special problems in the fields of physics, quantum chemistry and materials research.
But when it comes to concrete questions that only quantum computers can answer, experts have remained relatively vague. Researchers from ETH Zurich and Microsoft Research are now presenting a specific application for the first time in the scientific journal PNAS: evaluating a complex chemical reaction. Based on this example, the scientists show that quantum computers can indeed deliver scientifically relevant results.
A team of researchers led by ETH professors Markus Reiher and Matthias Troyer used simulations to demonstrate how a complex chemical reaction could be calculated with the help of a quantum computer. To accomplish this, the quantum computer must be of a "moderate size", says Matthias Troyer, who is Professor for Computational Physics at ETH Zurich and currently works for Microsoft. The mechanism of this reaction would be nearly impossible to assess with a classical supercomputer alone – especially if the results are to be sufficiently precise.
One of the most complex enzymes
The researchers chose a particularly complex biochemical reaction as the example for their study: thanks to a special enzyme known as a nitrogenase, certain microorganisms are able to split atmospheric nitrogen molecules in order to create chemical compounds with single nitrogen atoms. It is still unknown how exactly the nitrogenase reaction works. "This is one of the greatest unsolved mysteries in chemistry," says Markus Reiher, Professor for Theoretical Chemistry at ETH Zurich.
Computers that are available today are able to calculate the behaviour of simple molecules quite precisely. However, this is nearly impossible for the nitrogenase enzyme and its active centre, which is simply too complex, explains Reiher.
In this context, complexity is a reflection of how many electrons interact with each other within the molecule over relatively long distances. The more electrons a researcher needs to take into account, the more sophisticated the computations. "Existing methods and classical supercomputers can be used to assess molecules with about 50 strongly interacting electrons at most," says Reiher. However, there is a significantly greater number of such electrons at the active centre of a nitrogenase enzyme. Because with classical computers the effort required to evaluate a molecule doubles with each additional electron, an unrealistic amount of computational power is needed.
Source: https://phys.org/news/2017-07-clarifiying-complex-chemical-quantum.html
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