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Photo:  Martina Markus | Dieter Jacobi/Kölntourismus

An interview with Excellence Professor Sebastian Diehl on his research at the University of Cologne and on living in Cologne.

The interview was conducted by S. Rausch

Professor Diehl, you are an excellence professor. What does that mean?
Professor Sebastian Diehl (right) is Professor at the Institute for Theoretical Physics. Photo: Martina Markus

The Excellence Initiative is an instrument of German higher education policy intended to strengthen top-level research. In this context, two new professorships in theoretical physics were created at the University of Cologne. My profile is interdisciplinary: I deal with questions at the intersection of quantum optics and many-particle physics. This profile is quite unconventional – it is very promising, but also entails certain risks. The fact that this work is exceptionally well funded is a major strength of the Excellence concept.

I also want to stress that although the Excellence Initiative provides funding for a limited time period, the professorship will be funded in the long run. The University of Cologne’s commitment makes this possible.

Can you describe the research you are conducting here in Cologne? And how does it tie in with the Key Profile Area “Quantum Matter and Materials”?
The Institute for Theoretical Physics is hosted in a newly built building to provide first-class infrastructure for students and researchers. Photo: Martina Markus

There are always new things to discover at the intersection of different disciplines. The quantum mechanical many-particle systems which my working group is investigating are strongly driven by external fields such as laser light. This means that, in contrast to conventional many-particle systems, they exist in states of matter far beyond the thermodynamic equilibrium.

One major aim of my current research is to unravel new macroscopic phenomena that unequivocally reflect these microscopic non-equilibrium conditions. In order to achieve this, it is also necessary to develop new theoretical tools that can efficiently describe these externally driven quantum systems. At the same time, we are working on the design of experimental platforms that would allow us to test and further explore our theoretical predictions.

This research perfectly fits into the Key Profile Area “Quantum Matter and Materials.” The exciting thing is that although my work does not coincide with the Profile Area’s main research topics, there are many overlaps. That way, I can profit from existing expertise and provide new impulses for other people’s research.

How international is your research here in Cologne?
International cooperation plays a vital part in Sebastian's research. Together with his colleagues he organises Summer Schools in India. Photo: Martina Markus

My working group is involved in numerous international cooperation schemes. For example, I have very close ties to an international research center working in the area of quantum optics and ultra-cold quantum gases in Innsbruck, Austria. We also collaborate with the Weizmann Institute, the Scuola Normale Superiore in Pisa, Harvard University and ETH Zurich. All of these institutions offer great expertise in the many-particle physics of quantum-mechanical systems.

An important instrument in the training of doctoral students and young postdocs are summer schools. They give us the opportunity to convey the most pioneering research – beyond what the textbooks can tell us. This aspect is very important to me personally, and it is a good opportunity to get talented young researchers excited about my research area. In the past years, I visited several international research centers for this purpose, among other things in India and South Africa. This year, there will be summer schools on Crete and in Istanbul.

My appointment in the framework of the Excellence Initiative also allows me to host an international conference at the Institute of Theoretical Physics. That is planned to take place in the summer of 2017.

What made research here in Cologne interesting for you?
Research group Sebastian Diehl. Photo: Martina Markus

The research that is being conducted in physics at the University of Cologne is internationally competitive and highly diverse. At the Institute of Theoretical Physics, there are many experts in areas that complement my own research – form statistical mechanics via the physics of strongly correlated systems to mathematical physics. From the very beginning, that is, already during my appointment negotiations, I appreciated the openness of my colleagues toward my research. I already have plans for some very exciting collaboration schemes and look forward to working with my colleagues here in Cologne. From the vantage point of internationality, I can hardly imagine a better place to work. In the long run, I would like to work with colleagues from the area of experimental physics. They are also exploring systems beyond thermodynamic equilibrium. At the University of Bonn, there are experts in the area of ultra-cold quantum gases working both experimentally and theoretically. That is another interesting point of intersection with my research.

How do you like the city and the people? Do you feel at home in Cologne?
The view on the city from the other side of the river. Many new citizens describe Cologne as very openminded and they love the many green spaces that invite for relaxation. Photo: Dieter Jacobi/Kölntourismus

From the very beginning, I noticed people’s openness, friendliness and helpfulness. Probably that is not only due to the disposition of people in the Rhineland, but also to the international character of the city. For example, when I was trying to find an apartment in Cologne – no easy feat, by the way – I often stood around at street corners and didn’t know where to go. I was surprised to find that I never had to ask for the way. People offered me their help. That is only a small detail, but to me it seems characteristic of the region, and it certainly made for a very positive start for me here. Also, the range of cultural activities is immense. I am not very familiar with the surrounding countryside yet, but come spring, I’m planning to take long bike rides.