In memoriam: Helmut Rauch

Helmut Rauch passed away on September 2 2019, at the age of 80.

Professor Rauch was one of ILL's most prominent scientific users and CRG scientists, most famous for his development of a perfect-crystal neutron interferometer.  It splits a neutron beam into two coherent sub-beams which are spatially separated by several centimeters and are then recombined again showing interference fringes. This itself is remarkable, considering that at any moment the whole apparatus contains only one (!) neutron which interferes with itself. Thus, neutron interferometry has entered textbooks as a prominent example of wave-particle dualism. But beyond that, neutron interferometry has led to a series of breathtaking quantum physical experiments and still continues to do so.

Right after the first proof of principle in 1974 at the small 250 kW TRIGA research reactor of the Atominstitut in Vienna Helmut Rauch turned to the ILL to create a dedicated instrument for neutron interferometry. In collaboration with Prof. Ulrich Bonse from the University of Dortmund he established the CRG instrument S18 which he supervised until 2012.

From its commissioning in 1978 until today, S18 produced roughly one highlight every year, mostly in the field of fundamental quantum physics. Helmut authored more than 400 scientific publications of which about a third referred directly to the ILL and which witness his broad scientific interests far beyond interferometry. His concepts have inspired various other fields of physics. Neutron interferometry built the basis not only of modern matter-wave interferometry with atoms but also of quantum information and computation technology.

Moreover, neutron interferometry has become one of the most accurate methods to determine neutron scattering lengths. Helmut has put much effort in compiling and updating experimental information on scattering lengths and cross sections. Condensed in the perhaps most frequently consulted chapter in ILL’s “neutron data booklet” that he wrote together with W. Waschkowski, this effort stays an important legacy for the neutron scattering community as a highly appreciated source of valuable information.

Seeking innovative instrumental concepts to overcome the notorious lack of neutron densities in experiments has always been close to his heart. His intellectual efforts in this direction have led to various ideas for virtuous manipulations in neutron phase space. Well known are his ingenious proposals to use travelling magnetic fields for compression of neutron pulses. Unforgotten at ILL stays his project of a phase space transformer at PF2 using diffraction by moving crystals to convert ultracold neutrons into brilliant pulses of cold neutrons.

Throughout his professional career Helmut has invested much effort and dedication into the training of a next generation of researchers. Many of his scholars became leading scientists in their fields like Anton Zeilinger, Heinrich Kurz, Kurt Binder, Jörg Schmiedmayer, Gerald Badurek, Yuji Hasegawa, Peter Fierlinger...

Helmut used to be director of the Atominstitut of the Vienna University of Technology for more than 3 decades. He was member of ILL's Scientific Council and also did a lot to support Austria's scientific membership. He was member of the Austrian Academy of Sciences, the German National Academy of Sciences Leopoldina, and of the Academia Europea. Helmut Rauch received numerous national and international awards, including the “Schrödinger price” (1977), ”Ludwig-Wittgenstein price“ (2006), “Walter Hälg price” of the European Neutron Scattering Association" (2015), and the Austrian Decoration for Science and Art (2015), the highest distinction of the republic. In recognition of Helmut Rauch’s outstanding scientific achievements the Atominstitut was designated by the European Physical Society as an ‘EPS Historic Site’ on 22 May 2019 at the occasion of the international symposium ‘Quantum for Ever’, which was organized to honor Helmut’s 80th birthday.

The neutron community has lost a great man and an outstanding scientist. We will never forget him.