"I play with big and exotic computers"

Making quantum computers accessible through data centers

For Stefan Huber, there is no question that a lot is currently happening in the field of quantum computing. However, the mathematician does not get carried away with overly euphoric expectations and takes a relaxed view of the future of the new technology. Together with his team at the Leibniz Supercomputing Centre, he is working on expanding quantum computing as a new service for science.

By Maria Poxleitner

It does not come to Stefan Huber's mind to paint the future of quantum computing in bright colors. "There is no reason to be pessimistic," is his sober assessment. The 31-year-old physicist with a Ph.D. in mathematics is sitting in his office at the Leibniz-Rechenzentrum (LRZ). Green hoodie, jeans, red sneakers on his feet. "There are a handful of tasks where we know that a quantum computer is better than a classical computer, there are a handful of tasks where we know that it's not, and there are a lot of areas where we don't know anything at all," says Stefan, commenting on the status quo.

Nevertheless. New ideas in application research and the developments in recent years on the hardware side are sufficient motivation for the mathematician to focus his work at the LRZ on the question of how quantum computers can be made accessible to the users of the data center in the future. As a data center, one of the fundamental tasks of the LRZ is to provide computing resources to the scientific community and to ensure smooth operation. With the SuperMUC-NG, the LRZ even has one of the most powerful supercomputers in the world. Now, the goal is to expand quantum computing as a general service and enable scientists to access the new technology via a cloud.

What does it cost to compute on a quantum computer?

However, what is common practice with the SuperMUC-NG still raises many unanswered questions when it comes to quantum computers. Stefan is responsible for some of them: "One problem, for example, is that there is no established unit for quantum computing that is comparable to CPU hours." CPU stands for Central Processing Unit and refers to the main processors of computer hardware. Just as electricity has a cost and is billed in kilowatt-hours, the use of computing resources provided by a data center also incurs costs. The more and the longer the processors are used for a calculation, the more expensive it becomes. Eventually, billing is done in CPU hours. In the case of quantum computers, a meaningful unit still needs to be discussed, Stefan explains. One difficult question, for example, is how to take into account the time needed to calibrate the quantum computers: "The SuperMUC is completely unmanned, it just runs. The quantum computers, on the other hand, still need to be constantly tinkered with.“

The quantum computers at the LRZ are located in the QIC, the Quantum Integration Centre. There are several machines based on different platforms. One of the goals is to slowly prepare the devices for an unmanned environment, so that they can later be operated without a laboratory environment, explains Stefan. He himself is rarely in the QIC, however, because he is not a "laboratory physicist," as he says. During his studies, he was more interested in the mathematical side of physics.

Stefan Huber, 31


Staff scientist


Leibniz Supercomputing Centre (BAdW)


Physics & Mathematics

Stefan is developing solutions to enable quantum computing as a new service at the Leibniz Supercomputing Centre. This involves very specific issues, such as the costs that arise when using this computing resource. He also advises scientists on which of the various hardware technologies available at the LRZ is best suited for their particular research project.

Stefan in the "Q-Crew" office.

Born in Vorarlberg, a state in western Austria, he grew up in Lustenau, just 200 meters from the Swiss border, and therefore speaks both Vorarlberg dialect and Swiss German – "or whatever you speak there," Stefan adds with a barely perceptible smile. He went to ETH Zurich to study physics. The decision for the renowned university was initially a rather pragmatic one: it was the closest university geographically, Stefan says. "It was a welcome side effect that the university is also pretty good".

Coming from a family of linguists and literary scholars, he was a little out of line with physics, the 31-year-old says. "When I started studying, I thought I was interested in astronomy, but I quickly realized that wasn't my thing." In the end, it was quantum information theory that he found most interesting, especially the mathematical framework behind it. For his Ph.D., he moved from Zurich to Munich to the chair of mathematical physics at the Technical University. The problem he dealt with in his dissertation, namely how much information can be transmitted via a photonic channel, was motivated by physics. However, the main work – "It has its appeal to play around with functions and inequalities" – was relatively detached from the original question.

Learning how to manage big computers

After completing his Ph.D., the scientist initially took a position at the LRZ that was not directly related to his previous studies. "I did everything that had to do with server operation," says Stefan. At the time, there were no postdoctoral positions available in the research groups which he would have found interesting to continue his research, and he had always been interested in working with computers: "Since I was 15 years old, I have only used Linux on my personal computers." Before he seriously considered returning to research, it was already clear that there would be a quantum department at the LRZ. "And in the 1.5 years in between, it didn't hurt to learn how to manage big computers.“

With the SuperMUC-NG, a particularly big computer has to be managed at the LRZ. The rows of black server racks with the many interconnected computing units, the blinking LEDs and the roaring cooling system require their own floor in the so-called computing cube of the LRZ. Quantum computers, on the other hand, are still small – not necessarily in terms of spatial dimensions, but in terms of the number of qubits. "To my friends I always say that I play with big and exotic computers," Stefan says. Integrating quantum computers into classical supercomputers is another goal of the quantum department at the LRZ. "There are problems that we assume can be broken down in such a way that a large part can be calculated on a supercomputer and only a small part is outsourced to a quantum computer," the mathematician explains. There is therefore hope that for certain problems something can already be achieved with NISQ computers – that is, small and error-prone quantum computers – by using them as accelerators in classical supercomputers.

Although he is only 31 years old, Stefan is one of the old hands in his department. "I was the first member of the quantum group at the LRZ," says the scientist. It was only later that the group became an independent department. Stefan now has more than 30 colleagues working with him to realize the service “quantum computer” at the LRZ. He is a reliable contact person for his team – even when it comes to shedding light on the administrative jungle: "Since I've been working here for almost five years, I've already seen through the thicket of bureaucracy a bit, which is why the others often come to me for such things." When asked whether this bothers him, he shrugs: "That’s ok."

Karate and cubes

Stefan is also an old hand at his karate club, where he has been a member since he started at the age of six. He recently celebrated his 25th anniversary as a member. "Silver wedding, so to speak," he adds. As a teenager, he trained with the Austrian national youth team; today, he is involved in the club's management and is a coach himself. Every weekend, he travels from Munich to his old hometown of Lustenau to train a group of adults. He was lucky that it was the first sport he tried, says Stefan – "and I kept it”. What he likes about it: "The fact that karate is so versatile and there is something for all kinds of people.” During his studies he took a longer break from training. During this time, the time he had previously devoted to karate was given over to another hobby, which Stefan took no less seriously: "I participated in Rubik's Cube competitions.” Rubik's Cube is a kind of  cube-shaped puzzle in which all pieces of the same color must end up on one side of the cube. Solving the Rubik's Cube faster than his competitors filled his weekends back then. "I traveled a lot and even flew overseas to world championships," says Stefan, who at one point was ranked ninth in the world. Since he started doing karate every weekend again, he no longer actively participates in competitions. But of course he still solves Rubik's Cubes.

After a weekend dedicated to his personal hobbies, his head is free again to focus on his work at the LRZ. In the future, Stefan will spend more time advising scientists on which computing resources, such as which specific quantum computer platform, make the most sense for their particular project. What he particularly likes about this, he says, is the opportunity to see what is happening in his old field of research. "But not just in my sub-subfield, but more broadly." In Munich, also thanks to Munich Quantum Valley, there is now a whole range of groups working in the field of quantum information processing, Stefan notes, and one can exchange ideas with researchers and industry representatives from a wide range of backgrounds and specializations. "I like to keep an overview and see what is being researched in the various sub-areas."

For now, Stefan will stay with his Q-Crew, as they call themselves at the LRZ. "A lot is happening in this field at the moment, and a lot is happening quickly," says the mathematician. In a few years, we'll see if and how the field consolidates, and then we'll look further – "but it's not boring yet.”


Published 28 June 2024; Interview 30 April 2024