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Note on the Life and Work of Anatole Abragam

Serge Haroche
p. Quantum Physics

Notes de la rédaction

Source: La lettre, no. 33, May 2012

Texte intégral

1Anatole Abragam was born in 1914 in a middle-class Jewish family in Moscow, where he spent his early childhood and witnessed the initial years of Soviet Russia.

2He immigrated to France at age ten, with his mother and sister. His father, who had stayed in Moscow, was only able to join them in Paris eleven years later. From his childhood in Russia, he kept a perfect command of the language, as well as the essence of the Slavic soul, conveyed in his literature and poetry, which were part of him throughout his life.

3As soon as Anatole Abragam arrived in France, he rapidly adapted to his new world, learning to speak French fluently and without an accent within a few months. He performed brilliantly in secondary school at the Lycée Janson de Sailly, where he shone in mathematics and Latin. After completing his baccalauréat, he first turned to medicine, the profession of his mother, who was one of the first female doctors in Russia, but soon realized he was not made for a medical career and decided after a year to study physics. Too much of an independent mind to comply with the discipline of the classes préparatoires, he chose the university path.

4In the 1930s, despite a few distinguished professors, physics teaching in France was a very poor reflection of this discipline’s effervescence and revival, witnessed primarily in English-speaking countries and Northern Europe, where most scho­lars chased from Germany by the rise of Nazism had taken refuge. Quantum mechanics was still taught little or poorly in Paris and the young Anatole, with a sharp and critical mind, was well aware of the limits of the education that was being offered to him. He was unable to find a thesis supervisor at the Sorbonne capable of leading him beyond his Bachelor's, which he obtained with flying colours in 1936.

5He was starting to doubt his calling when the war interrupted his studies. He experienced the ‘phoney war’ and the German attack during his military service, without his unit being summoned to fight, and then hid out in the South, earning a living by giving Latin, maths and physics classes in private schools. He eventually took refuge in the Grenoble hinterland, joining the Free French Forces in the last year of the war.

6Aged 30, at the Liberation, he had neither a profession nor training in physics that lived up to his ambition, but new possi­bilities were opening up to him with the effervescence of France’s reconstruction. Unwilling to return to the Sorbonne and to his bad memories, he joined the École supérieure d’électricité (Supélec). There he learned the basics of radio-electricity and radiofrequency technology, which had made immense progress during the war, and knowledge of which was to serve Abragam later on. In 1947 his engineering degree allowed him to join the newly created Atomic Energy Commission. With three brilliant young graduates from the École polytechnique, he formed what they humorously called the “three musketeers” of the AEC, enthusiastically making up for lost time by studying the core texts of quantum physics in depth, using their complementary skills to translate them for one another from English, Russian and German.

7Most importantly, he obtained two assignments with leave of absence from the AEC, allowing him to travel abroad to complete his training as a researcher: first in Oxford, from 1948 to 1950, where he learned about electron paramagnetic resonance and based his thesis on original theoretical work on the subject; and then in Harvard, from 1952 to 1953, where he discovered nuclear magnetic resonance (NMR) under Edward Purcell, one of the pioneers of this discipline born in 1946.

8Back at the AEC, he was first asked to contribute to the nuclear and particle physics programmes that constituted the core mission of this organizsation, and worked in particular on designing a new accelerator. But he soon returned to the subject which had fascinated him since his time in America, the lighter physics of nuclear magnetism. In 1955 he created his own magnetism laboratory within the AEC, which, under various forms, was to be the world’s Mecca of NMR for the next 30 years. Thus, between ages 30 and 40, Anatole Abragam made up for lost time, becoming an internationally renowned researcher, recognized for his original contributions to the exploration of the properties of nuclear magnetic moments.

9His reputation was firmly established with the Principes du magnétisme nucléaire (Principles of Nuclear Magnetism), which he published in 1961, and which still constitutes a core reference fifty years later. Anatole Abragam’s great educational qualities shine through in this book, written in elegant English, for after his time at Oxford and Harvard, he spoke the language as well as he did Russian and French. In it he explains scientific calculations through images and analogies which lighten the text and make it easier for readers to understand. Anatole Abragam also wanted to express these educational qualities through direct teaching. From the mid-1950s, with other researchers from the AEC, including the three musketeers mentioned earlier, he invented high-level education designed as an introduction to modern physics, which was cruelly lacking­ in the regular curriculum of French higher education. The “informal” courses he and his colleagues gave for a few years to young researchers, including Claude Cohen-Tannoudji and Pierre Gilles de Gennes, and even to experienced scientists like Alfred Kastler and Jean Brossel, were the true precursors of the Graduate School education that was to develop in universities much later, in the mid1960s.

10But this was not enough to quench Abragam’s thirst to teach, and he dreamt of a professorship. University was not an option, as a thesis completed abroad, albeit in Oxford, would not afford him access to it. Alfred Kastler was the one who thought that the Collège de France was the solution to the problem and advised Anatole Abragam to apply! What institution could be better suited to his qualities than the Collège, which gives its professors total freedom in their teaching choices, allows them to express the full range of their theoretical and educational capacities, and above all as a legacy of François I’s distrust of the Sorbonne, does not require its professors to hold a degree from a French university. The matter was settled in 1960 when he was nominated for a chair at the Collège de France by Francis Perrin, not without all sorts of incidents that do not need to be discussed here.

11At the age of 45, Anatole Abragam, the late bloomer as he defined himself, became the young Chair holder of Nuclear Magnetism, which he remained for a quarter of a century. Every year he delivered highly valued education on diverse themes, stemming from his research at the AEC or the work of his colleagues, in France and throughout the world. During all those years, Anatole Abragam divided his time between tea­ching at the Collège de France and leading his research team at the AEC. For eight years, from 1962 to 1970, he was also Head of Physics at the AEC. This was an important administrative responsibility which allowed him to keep up to date on the evolution of many external research fields within and through which he contributed meaningfully to the evolution of the AEC. Along with the CNRS, the AEC became one of the most active multidisciplinary French research institutions. The reputation he acquired through the Collège de France, his research and his responsibilities at the AEC, came with numerous honours and distinctions, including entry to the Académie des sciences in 1973, nomination in several foreign academies and multiple international prizes, with only one exception, to which I will come back later. One distinction that was particularly significant for him was his nomination to the Pontifical Academy. A man of convictions, he nevertheless resigned a few years later to protest against John Paul II’s position on birth control.

12Drawing an outline of the major stages of Anatole Abragam’s career gives only a vague idea of his style and his important scientific contributions. He was an intuitive and prolific physicist, with a deep sense of aesthetics in science, always searching

13for the elegant idea and the simplest explanation, imagining new physical situations with a wealth of possible applications. A theorist before all else, he was very close to the experi­menters in his group, whose progress he followed attentively and with a critical mind. He kept himself informed on every detail, in which, he said, the devil was always hiding. It is difficult here for me to be more specific. I will simply say that he made crucial advances in our understanding of the phenomena involved in the magnetism of atomic cores in condensed matter, whether solid or liquid. These nuclei generally carry small magnetic moments (spins) associated with their kinetic moment. These magnets tend to orientate themselves within an external magnetic field or a field created by neighbouring magnetic moments. This orientation, thwarted by thermal agitation, can be modified by applying radiofrequency fields with the appropriate frequency, the very fields that the young Anatole learnt to produce and control in his years of engi­neering training at Supélec.

14By subjecting magnetic moments to such fields, Abragam and his colleagues (among them his collaborator for thirty years, Maurice Goldman) studied various effects related to the coupling of electron and nuclear spins with each other. They drew precise information on the structure of matter (the way in which these magnets are distributed) and on the dynamic mechanisms that disorientate the magnets, what we call their relaxation. They also invented ingenious methods for the dynamic polarization of these nuclear spins in an external field, transitorily obtaining much higher orientation rates than those observed in matter in its natural state. They were also able to produce a spontaneous orientation of nuclear spins in their internal field, what we call a state of nuclear ferromagnetism, and studied their properties.

15Anatole Abragam touched on many other research themes of the physics of nuclei and magnetism that I will not mention here. He nevertheless steered clear of two significant developments in NMR: the study of molecules of biological interest using this technique, and medical imaging. These were two fields within which pure physics relied on sciences in which he did not feel competent: biology and computing. It was these themes with significant applications in society that the Nobel committee distinguished when rewarding research on NMR, beyond the recognition paid to the pioneers of this field of physics, Edward Purcell and Felix Bloch. Abragam never hid the fact that he had hoped things would be different and that his more fundamental research would be recognized by this ultimate prize. He nevertheless took the Nobel’s decisions philosophically, even recognising the relevance of the