Tribute to Anatole Abragam

Back at the CEA, he was initially tasked with contributing to the nuclear and particle physics programs that were the organization's primary mission, and worked on the design of a new gas pedal. But he soon returned to the subject that had fascinated him since his stay in America, the lighter physics of nuclear magnetism, and in 1955 he set up his magnetism laboratory within the CEA, which, in one form or another, was to be a Mecca for NMR worldwide for the next thirty years. Thus, between the ages of thirty and forty, Anatole Abragam made up for lost time, becoming an internationally recognized researcher for his original contribution to exploring the properties of nuclear magnetic moments.

His reputation was cemented when he wrote Principes du magnétisme nucléaire (Principles of Nuclear Magnetism), published in 1961, which is still, fifty years on, an essential reference work. Anatole Abragam's great pedagogical skills shine through in this book, written in elegant English, for Anatole, after his sojourns at Oxford and Harvard, spoke that language as well as Russian and French. He uses images and analogies to lighten the text and make it easier for the reader to understand. Anatole Abragam wanted to express these pedagogical qualities in lively lectures. From the mid-1950s onwards, together with other CEA researchers, including the three musketeers mentioned above, he invented a high-level lecture program dedicated to an introduction to modern physics, which was sorely lacking in the normal curriculum of French higher education. The "unofficial" lectures he and his colleagues gave for several years to young researchers including Claude Cohen-Tannoudji and Pierre Gilles de Gennes, and even to established scientists such as Alfred Kastler and Jean Brossel, were the real precursors of the postgraduate doctoral teaching that was to develop at the University much later, in the mid-1960s.

But this was not enough to quench Abragam's thirst for lectures, as he dreamed of a professorship. The University was closed to him because a thesis defended abroad, even at Oxford, was not enough to open the doors. It was Alfred Kastler who thought the Collège de France was the solution and advised Anatole Abragam to apply! What institution was better suited to his qualities than the Collège, which gives its professors total freedom in their choice of readings, allows them to express the full range of their rhetorical and pedagogical abilities and, above all - a legacy of François ^I 's distrust of the Sorbonne - does not require its professors to have a degree from a French university. The matter was settled in 1960 at the instigation of Francis Perrin, but not without a few twists and turns, which need not be repeated here.

At the age of 45, Anatole Abragam - the butterfly belatedly hatched from his chrysalis, as he called himself - became the young holder of the Chair of Nuclear Magnetism, which he held for a quarter of a century, delivering highly appreciated lectures each year on a variety of topics, stemming from his research at the CEA or the work of his colleagues and friends in France and around the world. Throughout these years, Anatole Abragam divided his time between teaching at the Collège de France and leading his research team at the CEA. For eight years, from 1962 to 1970, he was also Director of Physics at the CEA, an important administrative responsibility which enabled him to keep abreast of developments in many fields of research outside his own, and through which he made a very positive contribution to the development of the CEA, which became, alongside the CNRS, one of France's most active multidisciplinary research institutions.

The recognition he received from the Collège de France, through his research and his responsibilities at the CEA, was accompanied by numerous honors and distinctions, including admission to the Académie des Sciences in 1973, appointment to several foreign academies and multiple international awards, only one of which is missing, as I'll come back to later. One of the distinctions to which he was particularly sensitive was his appointment to the Pontifical Academy. A man of convictions, he resigned a few years later to protest against John Paul II's position on birth control.

A broad outline of the major stages in Anatole Abragam's career gives little idea of his style and important scientific contributions. He was an intuitive and fertile physicist, with a deep sense of aesthetics in science, always seeking the elegant idea and the simplest explanation, imagining new physical situations rich in possible applications. Above all a theoretician, he was very close to the experimentalists in his group, whose progress he followed attentively and critically, keeping abreast of all the details in which, he said, the devil always comes to nestle. It's difficult for me to be much more precise here. Suffice it to say that he made essential advances in our understanding of phenomena linked to the magnetism of atomic nuclei in condensed matter, whether solid or liquid. These nuclei generally carry small magnetic moments associated with their angular momentum (spin). These magnets tend to orient themselves in an external magnetic field, or in the field created by magnetic moments in their vicinity. This orientation, counteracted by thermal agitation, can be modified by the application of radio-frequency fields of suitable frequency - precisely the fields that the young Anatole learned to produce and control during his years of engineering training at Supélec.

By subjecting magnetic moments to such fields, Abragam and his colleagues (including his collaborator of thirty years, Maurice Goldman) studied various effects linked to the coupling of electron and nuclear spins to each other, and derived precise information on the structure of matter (how these magnets are distributed) and on the dynamic mechanisms that disorient them, known as their relaxation. They also invented ingenious methods for dynamically polarizing these nuclear spins in an external field, transiently 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, a so-called state of nuclear ferromagnetism, and studied its properties.

Anatole Abragam touched on many other research topics in nuclear physics and magnetism, which I won't go into here. He did, however, stay away from two important developments in NMR. These were the study of molecules of biological interest using this technique, and medical imaging, two fields in which pure physics was becoming dependent on sciences in which he did not feel competent: biology and computer science. It was these themes, with their important applications in society, that were singled out by the Nobel Committee when it came to rewarding research into NMR, over and above the recognition given in 1952 to the pioneers of this physics, Edward Purcell and Felix Bloch. Abragam has never concealed the fact that he had hoped it would be otherwise, and that his more fundamental research would be recognized by this supreme prize. However, he took the Nobel's decisions philosophically, even acknowledging the relevance of the Stockholm committee's choices, which have always, by statute, singled out a specific important discovery rather than rewarding an entire career, however brilliant it may have been. He consoled himself with the humorous remark that, just as the President had given France a young Prime Minister, he had also given the Collège de France two young Nobel Prize winners, since it was he who had proposed in the early 1970s the creation of the chairs of Pierre-Gilles de Gennes and Claude Cohen-Tannoudji, both of whom would go on to enjoy the careers we know so well.

Beyond his personal scientific career, Anatole Abragam was one of the great architects of the return of French physics to the highest level of world research. Along with a number of other scientists of his generation, after the war he helped rebuild the bridges between the French scientific community and the world's leading physics schools, notably in England and the United States, creating the conditions that enabled new generations of physicists, including my own, to work competitively in a research-friendly environment. It seems appropriate in this eulogy to associate the memory of Abragam with that of other departed physicists of his generation, by recalling a few personal memories. The laboratory where I did my thesis, and where I still work, was founded in 1950 by Alfred Kaster and Jean Brossel, who devoted their careers to the study of the magnetism of atoms in the gas phase, as opposed to the atoms in condensed matter that Abragam studied. However, there is a great deal in common between these two physicists, which explains why Kastler, Brossel and Abragam knew and liked each other from the 1950s onwards, both scientifically and on a human level.

I've already mentioned how useful Abragam's lessons at the CEA were to Kastler and Brossel, and especially to their student Claude Cohen-Tannoudji, who then used the theoretical tools developed by Abragam to develop his theory of optical pumping. One of these tools is the pilot equation, which fully and accurately describes the behavior of atoms in an electromagnetic field in the presence of thermal agitation. When I began my thesis work with Claude, he introduced me to the beauties of the pilot equation and advised me to read the bible on the subject, the famous Principles of Nuclear Magnetism, enthusiastically evoking the atmosphere of the CEA lectures he had taken ten years earlier, which seemed to me to be shrouded in legend. Claude and I subsequently made constant use of this famous pilot equation, originally established by Felix Bloch, but so brilliantly explained by Abragam, which is used to explain so many phenomena in magnetic resonance, atomic physics and quantum optics, and which has been taught in lectures by three generations of Collège professors.

It was also indirectly that I was first exposed to the eloquence of Anatole Abragam. In 1967, as President of the French Physical Society, he had encouraged the writing of a book of essays in tribute to Alfred Kastler, who had just been awarded the Nobel Prize for his discovery of optical pumping. Jean Brossel, who had - incidentally - been unjustly forgotten by this prize, asked the young thesis student in his laboratory that I was to correct the proofs of this book. In Abragam's preface, I immediately came across the following sentences, a summary of his inimitable style:

The custom of jubilee volumes is not universally appreciated by the scientific community: an eminent physicist, whose collaboration had been imprudently solicited, thought he could qualify this kind of work as a collection of second-rate articles written by first-rate physicists. I take issue with this assertion: paying my own way, I made sure that second-rate physicists were not totally excluded from the common work..

I noted the self-mockery that I was later to find in my direct contacts with Anatole, and at the same time noted with a certain pride that, as the author of a contribution in this book, I had to belong to the same "second-order" category as Abragam, which wasn't so bad after all. But it was above all the phrase "j'ai tenu la main à ce que..." (I held hands with what...) that troubled me and which, knowing Anatole's origins, I attributed with a certain naivety and imprudence to a possible transcription of a Slavic expression into French. So I took the proofs back to Brossel with this sentence underlined in red and embellished with a question mark in the margin. I can still see Brossel's smile and his mischievous eyes, saying to me in his south-western accent (he had an accent, unlike the Russian Abragam): " Wretch, never correct Anatole's French ..."

Four years later, Claude Cohen Tannoudji insisted that Abragam should sit on my thesis jury, and so I had my first contact with him. The questions he put to me during my defense were incisive and precise, testifying to the extreme attention he paid to the work of a young researcher, to the breadth of his knowledge of physics and to his sense of humor. It was only much later that our relationship deepened. I had the opportunity to meet him at sessions of the Académie des Sciences, at congresses, or at convivial lunches or dinners with foreign colleagues visiting Paris. Like all those who knew him, I was able to appreciate his extensive knowledge of Russian, English and French literature. Like many Russians of his generation, he knew the poem-novel Eugene Oneginby heart, adored Tolstoy, Chekhov and Lermontov, and couldn't get enough of Shakespeare's plays, from which he borrowed lines for many of the exergues in the chapters of his books. His knowledge of cinema was impressive, ranging from the silent films of his youth to Woody Allen and the Coen brothers. His sense of humor was devastating, and he rarely gave up a good word, even if it was on the back of a colleague. He knew everyone who counted in world physics and had a story to tell about each one. He also had an inexhaustible supply of anecdotes illustrating all kinds of situations in the life of science, imbued with the Jewish humor that had never left him. The almost automatic appearance of all kinds of technical difficulties when experimenters try to carry out an experiment inspired by a beautiful theoretical idea in a concrete way was called in Abragam's group "the Margaret effect", in reference to the story he liked to tell: a matchmaker, an essential figure in Central European Jewish folklore, set out - a fine theoretical idea - to marry a son from a good family to the kindly princess, sister of the Queen of England, whose sentimental adventures were, at the time, reported in all the newspapers. After a long interview with the boy's family, whose reluctance she had, after much effort, succeeded in overcoming, the matchmaker exclaimed, rubbing her hands together: " Phew, half the job's done !

Another Anatole Abragam story came to mind on the occasion of a recent sensational scientific announcement. A well-known American physicist had published an article announcing the observation of a quark in the free state. As this is an elementary particle which theory predicts can only exist in bound form, hidden in the nuclei of atoms, this astounding news earned the physicist an hour of media fame. However, the delicate experiment could not be reproduced by other researchers, and the free quark, probably an artefact, soon disappeared from the headlines and from physicists' discussions. This ephemeral scientific bliss inspired Abragam to write a metaphor in which the elusive quark becomes a diamond: a man turns up one Friday evening, before closing time, in a large jewelry store, with a beautiful young woman who chooses a splendid ring. The man pays by cheque on the spot. The sales assistant informs him that, given the time of day, it's impossible for him to check with the bank that the cheque has been cashed. " Keep the ring until Monday, " he replies, " and I'll come and collect it when you've cleared it with the bank . Then he leaves on the arm of the beautiful, blossoming young woman. When he returns the following Monday, the sorry salesman tells him that the bank has refused the check. " I was afraid of that ," our man replies, smiling, " but what an excellent weekend I've had! The announcement of faster-than-light neutrinos would not have failed to inspire Anatole to write a similar fable.

But the brilliant, even caustic character also hid a simple, warm-hearted man. Abragam was kind and attentive to his students, colleagues and friends. He had met his first wife, Suzanne, during the war, and they were happily married for almost half a century. In delicate health, she was a constant companion on trips and at all the public events that accompanied her husband's professional life.

Having become a widower in 1992, Abragam made a donation to the Académie des Sciences to establish the "Suzanne and Anatole Abragam" prize, designed to perpetuate in the scientific community the memory of a united couple who, to his great regret, remained childless. He spoke of this departed companion with an emotion in which his love and admiration shone through. The private man was also evident in his affectionate relationship with his second wife, Nina, a Russian physicist he married in 1996, with whom he enjoyed a long and happy old age, "awaiting", as he put it himself, "the end of the story with serenity and without impatience". Finally, I'd like to mention Abragam's special links with the Collège de France. Of all the honors in his long career, it was his professorship at the Collège that made him proudest. He cherished the opportunity our institution gave him to meet so many outstanding colleagues, particularly in the humanities and social sciences (this was the era of Merleau-Ponty, Barthes, Foucault and Raimond Aron, whom he greatly admired). He saw our mission of teaching everyone about science in the making as a noble one, and appreciated the uniqueness of our institution on the world academic stage. Two anecdotes on this subject, taken from his autobiographical book, De la physique avant toute chose, illustrate Anatole Abragam's culture and spirit, and what he thought of the College's highly original mission.

The first relates to our motto, "Docet omnia". Anatole recounts how, in 1980, the Collège received with great pomp the President of the Republic who, as a man of culture, no doubt already thinking of the Académie française which was to welcome him a few years later, ventured in his speech to the teachers to complete our motto by adding the idea that we teach everything to everyone, transforming it into " Docet omnibus omnia ". When it came time to publish this speech, Anatole was happy to remind the literary professors, who, he said, had not noticed (but it's probably too good to be true), that the presidential omnibus was wrong, and that we should say " Docet omnes omnia " according to the immemorial rule of the double accusative (based on the classic example " Doceo pueros grammaticam "). Anatole adds that a very political discussion ensued as to whether to consult the President's office before making the correction, and that in his wisdom, the administrator decided instead to correct without saying anything. The second anecdote relates a dialogue between an American colleague and a Collège professor, the latter trying to explain to him what our institution is. The American, thinking he had understood, exclaimed: "Collège de France is like the Princeton Institute for Advanced Study! This comparison, which presents us as a copy of a foreign institution created four centuries after our own, reminded Anatole of an audience member's remark in Hamlet that the author must have read a lot of Freud.

Those who knew Anatole Abragam will remember his elegant silhouette, his smile, his fine, distinguished moustache, his gaze that could alternately be benevolent or sparkling with malice, and his clear, well-articulated voice that so often resounded in this hall. Anatole Abragam was a great scientist who had a considerable influence on physics through his scientific work, his lectures and his role as research director and administrator. Anatole Abragam was an honest man in the classical sense, a man of great culture and convictions. His influence in the academic world and his reflections on research and the University also made him a "sage" of science in the sense of the American "statesman of science" . The Collège de France can be proud to have counted him among its own.

Serge Haroche, April^1, 2013.