Jan Blomqvist

Jan Blomqvist, professor emeritus in theoretical nuclear physics at the Royal Institute of Technology (KTH), Stockholm, passed away on 16 October 2022 in his home in Stockholm.

Jan was widely respected and renowned internationally for his work on nuclear shell structure. He was also a highly appreciated colleague, for his friendliness and for his deep insights in quantum physics.

Jan was born in Stockholm on 18 May 1932. He began his career as a doctoral student at the Nobel Institute for Physics, Stockholm, in the 1950s. Soon he published his first work on the structure of the nucleus lead-209, of particular interest for understanding nuclear structure. This work received immediate international resonance and was later quoted in textbooks.

After his PhD, which he obtained in 1960, Jan was provided a fellowship to work at the University in Birmingham (UK) with Gerry Brown, one of the leading theoretical nuclear physicists at the time, thus starting a long collaboration and friendship that lasted until Brown passed away in 2013. In 1961–62 Jan continued his collaboration with Brown (who had become NORDITA professor in 1960) in Copenhagen, where he also started a collaboration and friendship with Aage Bohr and Ben Mottelson.

In 1964 Jan went to Stony Brook University in New York, where he continued his collaboration with Brown (then a professor at Princeton) and with other leading theoretical nuclear physicists, in particular Akito Arima. Much later, when Arima was the vice chancellor of Tokyo University, he attended a meeting organized by Stockholm University to discuss collaboration prospects. In the reception arranged in Arima’s honor, Jan was invited as an extraordinary guest.

At Stony Brook, Jan developed, together with Tom Kuo, an effective nucleon–nucleon interaction that became widely used for realistic nuclear structure calculations. In 1974 he worked at CERN performing theoretical work and supporting the experimental activities at the ISOLDE facility that had just started.

Jan’s fruitful collaborations with leading experimental physicists are particularly noteworthy. In this context it is worthwhile to mention his work together with Peter Kleinheinz in Jülich, Germany, where outstanding research was performed. Kleinheinz sometimes visited Stockholm and would lock himself with Jan in an office to discuss physics. When asked why he “kidnapped” Jan in such a fashion, Kleinheinz replied that it was a rare occasion when he could enjoy listening to a master speaking with profound clarity and precision.

Even other German researchers, like Hubert Grawe, were very impressed with Jan’s work. Grawe used to say that beyond the physics that Jan was developing, it was art.

Jan had a particular fondness for physics in the Nordic countries, which he encouraged through his position as Nordic Program Committee member in NORDITA. This was particularly the case in Oslo, with Osnes and one of us (MHJ) who had Jan as opponent in his PhD thesis.

The quality of the work of Jan was emphatically expressed by an international committee evaluating the research groups in Sweden for the National Research Council. It was said that the research work of Jan “is already classical.”

Jan remained active after his formal retirement in 1997, even working extensively from home. He considered this more as a hobby than work, but he took it quite seriously and contributed to outstanding research during his post-retirement years. An example of this was his realization that in the nucleus palladium-92 and heavier spherical self-conjugate nuclei, special, isoscalar, neutron–proton correlations should manifest themselves as a new spin-aligned proton–neutron paired phase. Evidence for this effect was identified by the KTH group and collaborating physicists at the accelerator laboratory GANIL in France and was published in Nature in 2011, 14 years after Jan’s formal retirement.

We are happy and thankful for having had the privilege of being among his collaborators.

Jan is survived by his three sons and their families. He will be deeply missed also by his many friends and colleagues.

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