With Jülich support, a quantum computer of Google has solved a task that currently no classical computer can handle. Jülich expert Prof. Tommaso Calarco from the Peter Grünberg Institute (PGI-8) explains why this quantum supremacy could become as important as the first motorised flight of the Wright brothers.
I am a layperson: can you explain to me what problem the Google quantum computer has solved?
Actually, no. It’s an abstruse mathematical problem with no practical use, in which one throws the dice many times with the quantum computer, so to speak, and calculates the random distribution of the results. Understanding the problem isn’t easy, even for experts. The Google team chose it because it’s suited like no other to demonstrate the supremacy of the quantum computer over the classic computer. In other words: the relatively few functional qubits that can be generated so far are sufficient for it. Qubits are the quantum counterparts of bits. The Google quantum computer solved the task with 53 qubits in less than five minutes – according to Google, it would take the world’s fastest supercomputer several thousand years.
Picture above: Let’s just fly: Orville Wright in November 1904, barely a year after the maiden flight. Initially, the Wright brothers did not solve an urgent problem with their flying machines at the beginning of the 20th century – and yet they changed the world.
A calculation without any practical value – isn’t this rather sensationalism than a scientific breakthrough?
This impression is completely wrong. It’s a great scientific achievement. I’m particularly enthusiastic precisely because it’s a result of basic research. Anyone who only asks about the direct benefit of a result – as is often the case – will at best get the innovation of tomorrow, for example a car with a few per cent less fuel consumption. But if you hold back a little on the question of benefit, you might get the innovation of the day after tomorrow.
The physicist Tommaso Calarco is considered one of the leading experts in quantum computing. He is one of the initiators of the Quantum Flagship of the European Commission and Chairman of the Quantum Community Network, a network of high-profile members of the quantum technology community.
According to a computer scientist from the US, the current computing success of the quantum computer is reminiscent of the Wright brothers’ first flight, as this flight did not solve any urgent problem at first. Is it an apt comparison?
Yes, I find the comparison very fitting. The Wright brothers’ first motorised flight in 1903 was a twelve-second short hop, which initially created no new means of transport and had no practical use. Today, it’s no longer necessary to explain to anyone that air transport has changed our world enormously.
Had you expected that the supremacy of the quantum computer would be successfully proven?
This is another reason for my enthusiasm: a few years ago, I would never have dreamed that quantum supremacy could be demonstrated before my retirement.
How old are you, then?
I just turned 50.
So quantum computer development is about 15 years ahead of your expectations. Google has surged ahead. Can others still catch up with the company now?
Yes. Scalability is considered a major challenge which even Google has not mastered yet: you need thousands of qubits that are as perfect as possible in order to perform really useful calculations. It’s still completely open who will be ahead in the end. Perhaps the IBM corporation will overtake Google in this respect. We in Jülich are also building a quantum computer with funding from the European flagship initiative, involving components from all over Europe. It’s not so important whether we reach the next milestones before or after these corporations. The crucial thing is that we do not want to be dependent on American or Chinese companies. After all, export stops may occur: we would then suddenly no longer be able to buy quantum computers from Google, for example.
Google’s quantum computer is based on superconducting circuits. Does this mean that other technologies with which quantum computers could basically be built are out of the picture?
Again, no. It’s still completely uncertain which technology may provide thousands or even millions of qubits that are as faultless as possible. Therein lies a great opportunity for Europe as well: for example, we also research and develop quantum computers based on ion traps or optical traps. We Europeans have access to laboratories, infrastructure and skills that have been greatly expanded in recent years. Google or other companies, on the other hand, would have to start from scratch if they wanted to switch to these technologies.
Jülich operates conventional supercomputers of the highest performance class. Doesn’t this compete with the prominent role of Jülich in the European quantum computer initiative?
On the contrary. Until we have millions of perfect qubits, we must ensure that the precious qubits only do what they are unbeatable at doing. No quantum computer resources should be wasted on anything a classical computer can do. This includes the entire preparation of the actual calculation. For the foreseeable future, it’s imperative that supercomputers and quantum computers work together.
“Quantum supremacy” means the point in time at which a quantum computer is, for the first time, superior to a conventional computer in a particular task. Proving this was considered a great challenge. In September 2019, Google announced that it had achieved this quantum supremacy. Researchers from the Jülich Supercomputing Centre (JSC) headed by Prof. Kristel Michielsen were also involved in the scientific publication on the evidence. By means of simulations on the Jülich supercomputer JUWELS, they helped to verify the results and determine the performance of the quantum processor.
When will there be a quantum computer that can be used in practice?
In the European Quantum Flagship, we have agreed on the following answer: it will take at least 10 to 20 years. It worries me when some companies give the impression that quantum computers will soon be able to solve all problems. This exaggeration almost inevitably leads to disappointment – thus harming our field of research and society. Fortunately, the European Commission and the German government have meanwhile realised that staying power is essential for success in the development of quantum computers.
The interview was conducted by Frank Frick.
Photos: Forschungszentrum Jülich/Sascha Kreklau, Everett Historical/shutterstock.com