UNIVERSITY OF COLOGNE International

Photos: Martina Markus / Janez Pelko / Zala Lenarčič

Seabreeze, sunsets and physics

Zala Lenarčič is a postdoctoral fellow in the group of Professor Achim Rosch at the Institute for Theoretical Physics at the University of Cologne. She is part of CRC 183, a new Transregional Collaborative Research Center involving an international collaboration of the University of Cologne, Freie Universität Berlin, the University of Copenhagen and the Weizmann Institute of Science in Israel. Under the title 'Entangled States of Matter', the mission of the CRC is to explore and exploit the role of entanglement in the quest for quantum computers.

Twice a year members of the CRC from Berlin, Cologne, Copenhagen and Rehovot (Israel) get together to exchange ideas, present already accomplished results and set directions for future physics projects.

A report by Zala Lenarčič

Kick-off in Langeoog

Back in November 2016 the newly established community of CRC 183 members met in Langeoog. That was the first meeting after our research center had been launched. Of course many of the Principal Investigators (PIs) who represent the pillars of the projects within CRC 183 attended the conference. However, it was even more important that young researchers at the doctoral and postdoc level got the chance to meet, learn about each other’s expertise and exchange ideas.

Gathering on the tiny island Langeoog, one of the German East Frisian Islands located in the North Sea, did not provide for a particularly cosmopolitan flair. Yet I noticed that the discussions during and after the talks benefited strongly from the international audience. Overall, the atmosphere was much livelier than at a typical seminar in Cologne. However, this was not only due to the participants’ different nationalities, but to the fact that everyone in the room was interested in and working on diverse but sufficiently related topics. It is exactly this diverse cohesion that makes our CRC so distinct and promising.

Discussing physics at the beach

Conferences such as the one in Langeoog are absolutely crucial for international cooperation, since they bring researchers together and provide them with the chance to engage in intensive brainstorming activities, which can never be done in the same way via Skype, for instance. As far as I know, this was also the argument in favor of this rather remote and small location: to have everyone in the confined space of a provincial town: Langeoog! No one was able to escape further than to the beach, where you would naturally meet a pleasant companion for discussion of some interesting matters in physics.

In the CRC’s structure, each project is typically headed by PIs from different areas of expertise, which is good as it enables the research teams to apply different approaches to the same problem. However, it is also challenging to establish feasible communication channels. Besides facilitating exchange and communication, such conferences as the one in Langeoog also create a map of activities, especially useful for younger members who do not know the whole project proposal in detail. In my specific case, it helped me to get in touch with a postdoc from FU Berlin working on the topic of driven open systems, whom I have never met before despite similar interests. I hope that we will manage to continue our dialogue initiated in Langeoog.

With regards to the concrete project that I am involved in, I am really glad that our group’s mainly analytical approach towards the manipulation of topological defects (storing quantum information) in a disordered and interacting system, which is headed by Professor Rosch from the University of Cologne, will be complemented and supported by numerical DMRG (Density Matrix Renormalization Group) calculations provided by the research group of Dr. Karrasch at Freie Universität Berlin.

In general, coming from Slovenia, where funding, cooperation and networking is done on a much smaller scale, it is certainly a valuable insight to be part of a diverse and international cooperation project such as CRC 183. Working in such a co-creative environment also provides young researchers with different opportunities to progress in their academic careers. For instance, especially doctoral students are encouraged to spend some time at other research center’s institutes, a valuable experience that sometimes helps to broaden rather narrow doctoral theses. Another format that was suggested at the conference in Langeoog is the organization of small and rather spontaneous workshops involving up to 15 people, not necessarily members of our CRC, but also external experts on one particular topic. All these activities certainly contribute to a more lively research atmosphere in Cologne.

About the CRC 183 Entangled States of Matter

CRC 183 is a new Transregional Collaborative Research Center involving an international collaboration of the University of Cologne, Freie Universität Berlin, the University of Copenhagen and the Weizmann Institute of Science in Israel. Under the title Entangled States of Matter it researches the role of entanglement in the quest for quantum computers. A quantum state is entangled when the objects it describes are strongly interwoven. Such types of states play a fundamental role in quantum computation. As opposed to classical bits, a quantum bit (qubit) can be in a simultaneous superposition of the 1 and 0 states. Entangling several qubits together is necessary for the implementation of quantum computation. The realization of such computations strongly depends on the stability of quantum bits against errors induced by the environment. A promising error protection mechanism is to use entangled states of topological origin. These states are 'knotted' in a non-trivial way, yet can be realized in realistic condensed matter systems. The aim of CRC 183 is to understand the preparation and manipulation of such quantum bits, and to explore and exploit the protection mechanisms that ensure their stability. By merging concepts from quantum information and condensed matter physics it aims to design and realize devices for 'topological quantum computation'.