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Ernst Brun studied physics at the University of Zurich and received his doctorate in 1954 under Professor H.H. Staub with a thesis on magnetic nuclear moments using nuclear magnetic resonance. He developed new experimental methods - dynamic nuclear polarization - to amplify nuclear magnetic resonance signals and thus was able to detect very weak signals. After a research stay in the USA, he was appointed associate professor of experimental physics at the University of Zurich in 1958. In 1963 he was promoted to full professor.
Brun initially worked on nuclear magnetic resonance (NMR) and its applications to the structural analysis of minerals. His close collaboration with crystallographers in Switzerland and abroad stemmed from this period. Later, he focused his diverse scientific activities on the study of complex nonlinear systems using NMR and laser methods, which led to the discovery of the NMR laser (Raser) in his research group. He also made increasing use of extensive simulation calculations based on spin dynamics and spin thermodynamics, as exemplified by the development of the Raser: It started with the observation of non-linearities in the signal strengths of the nuclei at strong negative polarization. Based on model calculations with extended Bloch equations, he postulated that a nuclear spin system should spontaneously emit coherent radio frequency radiation when the degree of polarization reaches a certain threshold. Following extensive experiments, he finally succeeded in realising experimentally this nuclear resonance laser or Raser. He interpreted the spontaneous transitions of the disordered system to a coherently radiating highly ordered state and the complex transient processes occurring in the process with theories of phase transitions and with chaos theoretical principles (chaos and order). The insights gained were often of a very general nature and can be applied to many areas of the natural sciences.
Ernst Brun’s research was characterized by curiosity and enthusiasm. He successfully transferred this permanently to his colleagues. He was open to many new ideas, which he discussed critically, thus pursuing new paths with conviction, both mentally and materially.
In addition to his profound special lectures, Ernst Brun taught medical students for many years as a great and dedicated teacher in lectures that remained in the memory of many former students. In doing so, he succeeded in conveying to his audience the fascination of researching fundamental physical questions, and in introducing physics as a basic subject to the future natural scientists.
Ernst Brun served as Dean of the Philosophical Faculty II (today Faculty of Mathematics and Natural Sciences) from 1970 to 1972 and as Director of the Physik-Institut of the University of Zurich from 1972 to 1992. He was a charismatic and very people-oriented institute director who emphasised a collaborative management style. Important decisions were taken together with the people concerned and were presented and discussed at institute meetings. In this way, he made a significant impact in ensuring that no one felt advantaged or disadvantaged and that a good atmosphere was created throughout the institute. The welfare of all was always more important to him than personal success or honours. The Physics Institute under the leadership of Ernst Brun was marked by unity with a sense of community, which was shaped and fostered by his extraordinary personality.
The University of Zurich, colleagues and former students lose in Ernst Brun a person and teacher to whom they owe much.
Katharina Mueller
