A Quantum Computer Builder

Prof. Stefan Filipp is newly appointed as chair for Technical Physics at the Physics Department of the TU Munich and Director of the Walther-Meißner-Institute of the Bavarian Academy of Sciences and Humanities. He is also Core PI in the Munich Center for Quantum Science and Technology (MCQST).
In this interview, he shares on his passion for quantum theory, returning to academia, and on the future of quantum computing in Munich.

A Quantum Computer Builder

The walls are still bare; the air smells of paint. Unpacked moving boxes are stacked in the office. The laptop on the desk looks somewhat neglected, and there are two chairs provisionally placed near the round table in the meeting corner. Due to corona, the new director of the Walther Meißner Institute (WMI) started work a few weeks later than planned. Curious and full of expectations, Stefan Filipp is still looking forward to his job as Director of the Institute for Low Temperature Research, which he has now had for a few days.

It drew him from Zurich to Munich in part because it would bring his wife and four children a little closer to his home of Vienna. And naturally he also wants to help the quantum computer in Munich take a leap ahead. Stefan Filipp has dealt with quantum phenomena for a long time. During his studies, Bell’s theorem was very popular, but there were hardly any lectures on it. Anton Zeilinger’s experiments and a seminar on quantum physics and entanglement left their mark: A fascinated Filipp discovered that you can use lasers to do very beautiful experiments with photons. However, soon he was not as concerned about explaining physics. Rather, he was captivated by the idea of making something out of it. In application, i.e. in quantum computers, he saw that they have the potential to achieve something truly new. The idea of being able to make his own contribution here encouraged Stefan Filipp to address quantum phenomena in more depth.

When neutron interferometers are part of everyday life

The Austrian physicist initially wanted to remain more in the area of theoretical physics. He completed his Master’s degree in Sweden as part of an Erasmus program, where he also studied the correlations between quantum states: the so-called geometric phases. The next stop in his career brought Filipp back to Vienna, to Professor Rauch at the Atomic Institute. He wanted to continue with theory there. However, it was discovered fairly quickly that it was hardly possible to deal solely with theory at an experimental institute. Sooner or later, every scientist had to personally participate in the experiments there.

Suddenly, a neutron interferometer became part of Stefan Filipp’s daily life. He irradiated silicon crystals with neutrons. The beam is broken and can be reunited. In these interferometry experiments, you measure peaks or you don’t, depending on the interference pattern used to set up the experiment. Filipp was fascinated that you could actually consider quantum phenomena in a measuring apparatus. Undoubtedly, it was necessary to struggle through many hard steps in such experiments. “But when everything comes together, when you have the experiment in the box and see the data appear on the computer screen, and these data show what you actually suspected, that is a really nice feeling.”

From neutrons to photons to quantum optics

So Stefan Filipp stuck with screwing and cable laying and experimented with ultracold neutrons. But these single particle systems could not really convince him. Neutrons as single particle systems were not so convincing for practical quantum information processing. And so the search for more promising and seminal research objects led him to Andreas Wallraff at the ETH Zurich. This is where the first experiments in quantum optics were done, where individual qubits, individual superconducting circuits, and photons are coupled. This basically involved the second generation of experiments with qubits. They began at Yale with Robert J. Schoelkopf and in Santa Barbara with John Martinis. Wallraff was a postdoctoral student under Schoelkopf and did experiments at the ETH. Back then, there were roughly ten groups that worked in the area. Now there are quite a few more, and industry has jumped on the train as well in the meantime. IBM was involved early on and set up a group with Mattias Steffen and Jerry Chow, who come from Schoelkopf and Martini, to build very actively functioning quantum computers.

A quantum computer for research in Munich

Filipp’s group in Munich will obviously not compete in the commercialization of large-scale quantum computers. Rather, the goal is to find possibilities for improving the system itself. “The vision would be to build a system that is sufficiently large – but that does not mean it has to be hundreds, thousands, or millions of qubits. However, it should be a system with ten, 20, or 30 qubits and perhaps even more if there are enough resources.” According to Filipp, you need this size in order to understand how a system functions. That was ultimately one of the reasons why he headed to the WMI in Garching. By no means does the Austrian quantum expert only want to deal with engineering in the novel supercomputer, which was the focus of his work at IBM. Rather, he is curious about increasingly entering basic research: “I want to be driven only in part by the application and also immerse myself in scientific curiosity.” According to him, he is able to pursue the question of what new qubits, new coupling mechanisms, or materials could look like, along with other interesting issues. You need input and research from various areas for this.

Stefan Filipp has no doubts about whether this can all be achieved. Rather, he is convinced that things will remain exciting at the university. As he says, ultimately, you can choose areas that you want to examine in more depth. And even if it does not involve building a commercial quantum computer, Filipp is confident that the technology behind it is sensible and can be useful, irrespective of the question of what the first application of it will actually be.

A strong network of quantum scientists

However, certain general conditions are required to set up a functioning system. Filipp found that these conditions were met at IBM’s research center. Many people with a lot of expertise work at a very high level there. When chatting daily over coffee in the cafeteria, employees exchanged ideas freely. In Munich, that is not so easy, alone due to the size of the campus. That is why the MCQST is here. This brings quantum scientists together at various events and offers them the opportunity to discuss, for example. “And the better you can network there, the better you can become integrated into the ecosystem and the more you can get out of it,” says Filipp convinced.

Filipp will also bring something else to Munich: daily trips to the office with his e-bike. In hilly Zurich, he had to travel around 16 km to the institute, and it will be 20 km now to the still empty office at the WMI – the route is flat, that is, ideal for his e-bike.

About Stefan Filipp

Dr. Stefan Filipp has been Professor of Physics at the TU Munich and Director of the Walther Meißner Institute of the Bavarian Academy of Sciences since May 2020. Before that he worked at IBM Research, where he had been at the Watson Research Center in New York, USA, in the area of the superconducting circuit quantum computer since 2014. In September 2015, Stefan switched to the IBM Research Laboratory in Zurich. There he handled the technical management of the team for superconducting qubits.

Before joining IBM, Filipp worked from 2008 to 2014 at the Quantum Device Lab of the Swiss Federal Institute of Technology (ETH) in Zurich. There he researched hybrid cavity QED, geometric phases, quantum optics, and quantum information processing with superconducting circuits.

Stefan received a doctorate (with distinction) in technical physics from the Vienna University of Technology in 2006. For his doctoral thesis, he was awarded the Victor Hess prize from the Austrian Physics Society (Österreichische Physikalische Gesellschaft).

He completed his Bachelor’s degree in technical physics at the Vienna University of Technology in 2003. He received a Master of Science in physics from Uppsala University (Sweden) in 2002.


Prof. Dr. Stefan Filipp
Physics Department | Technical University of Munich
Walther-Meißner-Institute - Bayerische Akademie der Wissenschaften
Walther-Meißner-Straße 8
85748 Garching
Tel.: +49 89 289-14201
E-Mail: stefan.filipp@tum.de

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