With their rapid development, quantum computers are already scratching the limits of the best supercomputers. However, with their high computing power, they are vulnerable to environmental influences - incorrect calculations can be the result. A simple method provides a solution.
Errors that are so complex that scientists can no longer check them on classical computers are particularly serious. Nevertheless, to use quantum computers reliably, researchers need a method that allows them to check the result of the calculations. And they can do so without knowing the correct answer.
A team of physicists from Austria, Singapore and the UK has taken the challenge and reached a creative conclusion: They let quantum computers compete against each other. »We have several quantum computers perform random-looking calculations«, explains Martin Ringbauer of the University of Innsbruck. »What the devices don't know, however, is that there is a hidden connection between the calculations«.
In this case, the researchers use complex entangled quantum states, from which many different calculations can be derived. Although the results from each quantum computer are random, they must always match in certain aspects because of the hidden connection, Ringbauer says. If the results match, the computers have calculated the right thing.
The international research team demonstrated the new method on five quantum computers at the Universities of Innsbruck and Vienna. It shows that quantum computers can be tested against each other using any hardware. If the results of the different calculations on the computers match, they have calculated the right thing.
With the new method, however, it is not necessary to read out the entire result - a very time-consuming process. It is enough to check how often the two devices agree. This is also a practical procedure for very large quantum computers. Thus, the method is applicable to many current as well as future quantum computers.
Technische Universität Wien