A TÜV for quantum computers

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A TÜV for quantum computers

Research team led by physicist from Freie Universität Berlin develops quality tests for quantum computers

Quantum technologies, and especially quantum computers, are considered a promising technology for the future. It is hoped that they will solve problems that even the fastest supercomputers are currently practically unable to handle. Large global IT companies and countries such as the U.S. and China are investing significant sums in the development of the technology. But because quantum computers are based on different physical laws than conventional computers, laptops or smartphones, they are more prone to failure. An interdisciplinary research team from Freie Universität Berlin, Helmholtz-Zentrum Berlin, Heinrich Hertz Institute, QuSoft in Amsterdam, Quantum Research Center in Abu Dhabi, QMath in Copenhagen, and Technische Universität München has now found out how to test the quality of such quantum computers. The study has been published in the journal "Nature Communications" ( ’023 -39382-9). The scientific "computer test" uses methods from physics, computer science and mathematics.

Jens Eisert, a renowned quantum physicist at Freie Universität Berlin and one of the study’s authors, explains: "Quantum computers work on the basis of quantum mechanical laws of physics, in which individual atoms or ions are used as computational units, i.e. controlled, tiny physical systems. What’s extraordinary about future computers is that at this level, nature works in an extremely and radically different way than we know in our everyday experience of the world we perceive."

However, quantum computers also have a weak point: "They are true mimosas when it comes to interference from the environment. If the quantum computer is not sufficiently shielded from the environment, the properties that are responsible for its computational power disappear. The ’quantum advantages,’ as they say, disappear. In short: Then it doesn’t work," the professor of theoretical physics continues.

For research, therefore, the important question arises: How can one actually know whether a quantum circuit has functioned correctly? Similar to the way TÜV tests whether a car is still safe to use on the road, test methods are needed that show the quality to which a quantum circuit has been implemented. Without such methods, you get results in quantum computation, but you can’t rely on them," says Jens Eisert.

The interdisciplinary research team from Freie Universität, Helmholtz-Zentrum Berlin, Heinrich Hertz Institute, QuSoft in Amsterdam, Quantum Research Center in Abu Dhabi, QMath in Copenhagen, and Technische Universität München has now figured out how to test the quality of such quantum computers.

The method is as simple as it is amazing: You perform certain completely random quantum circuits and then read out the elementary parts of the quantum computer, called ’quantum bits,’" continues the professor of theoretical physics at Freie Universität Berlin. The data obtained in this way allow for a whole range of diagnostic information. From the same data, one can learn how well elementary gates, i.e. computational units, work, what interferences are present or whether certain parts interact with each other unintentionally.

To use the metaphor of the TÜV, it’s like randomly going over the car several times with a washcloth in a few swift movements. And would thus find out whether the engine is working, the windshield wiper fluid is filled and the brakes are properly adjusted: All this, with the same random measurement. Such a measurement provides the entire diagnostic in one sweep," emphasizes Jens Eisert.

With the help of this method of verification, researchers hope to turn quantum computers into real technological devices that can actually be used economically and scientifically in the future. (cxm)