Claude Cohen-Tannoudji

Claude Cohen-Tannoudji was born on 1 April 1933 in Constantine, Algeria, then part of France, to Abraham Cohen-Tannoudji and Sarah Sebbah. He was the eldest of three children in a modest Sephardic Jewish family. In his Nobel autobiography he explained that his family came from Tangier and had settled in Tunisia and then Algeria in the sixteenth century after fleeing the Inquisition in Spain, so that the name Cohen-Tannoudji simply meant the Cohen family from Tangiers. Algerian Jews had obtained French citizenship in 1870.

His father was self-taught but intellectually restless, reading biblical and Talmudic texts as well as philosophy, psychoanalysis and history, and he passed on a love of study, discussion and debate. The family moved to Algiers in 1938. From autumn 1940 the Vichy regime stripped Algerian Jews of their French nationality and imposed quotas in schools; these measures did not end until October 1943. He later wrote that the American landings in Algeria in November 1942 had saved his family from the Nazi persecutions spreading across Europe.

He completed his secondary schooling at the Lycée Bugeaud (now Lycée Emir-Abdelkader) in Algiers, followed by three years of preparatory classes, and in 1953 came second in the entrance examination of the École normale supérieure in Paris. He left Algiers just before the Algerian War.

At the ENS from 1953 to 1957 he studied mathematics with Henri Cartan and Laurent Schwartz, but Alfred Kastler's physics lectures were, in his words, so stimulating that he switched to physics. In 1955 he joined the optical pumping group of Kastler and Jean Brossel for his diploma work and spent two months that summer at the Les Houches summer school in the Alps. He passed the agrégation in physical sciences in 1957.

After 28 months of military service, he returned in early 1960 to prepare a doctorate under Kastler and Brossel as a CNRS research associate. Working on the theory of the optical pumping cycle with Jean-Pierre Barrat, he predicted and then observed the light shift of atomic sublevels, now known as the AC Stark shift, and defended his doctorat d'État in December 1962.

From 1964 he taught at the Faculty of Science of the University of Paris, as a lecturer until 1967 and then as a full professor until 1973, teaching quantum mechanics at graduate and undergraduate level. His group, which included Serge Haroche, Jacques Dupont-Roc, Gilbert Grynberg and Claude Fabre, developed the dressed atom approach, treating an atom and the photons it interacts with as a single system with true energy levels. With Serge Reynaud he applied it to resonance fluorescence and photon correlations in intense laser light.

In 1973 he was elected professor of atomic and molecular physics at the Collège de France, a chair he held until 2004. His weekly lectures, given in chalk on a blackboard and followed by a seminar, drew large audiences from across French physics. In the early 1980s he began lecturing on radiative forces, and in 1984 he invited Alain Aspect to join him and Jean Dalibard in a new experimental group on laser cooling and trapping, joined a year later by Christophe Salomon and from 1993 by Michèle Leduc.

The group demonstrated the first confinement of neutral atoms in regions the size of an optical wavelength and introduced the name Sisyphus cooling in 1986. When William D. Phillips observed unexpectedly low temperatures in 1988, Cohen-Tannoudji and Dalibard explained them through a low-intensity version of the Sisyphus effect, as Steven Chu's group did independently. With Aspect and Ennio Arimondo they then developed velocity-selective coherent population trapping, which cools atoms below the single-photon recoil limit, and later analysed it with Jean-Philippe Bouchaud using Lévy statistics.

These advances earned him the 1997 Nobel Prize in Physics. Cold atom physics has since grown into Bose-Einstein condensation, quantum simulation of many-body systems and atomic clocks of unprecedented accuracy. He was a visiting professor at MIT and Loeb Lecturer at Harvard in 1976, and remained an honorary professor at the Collège de France after 2004.

Teaching was central to his life. His lecture notes at the University of Paris became Mécanique quantique, written with Bernard Diu and Franck Laloë and published in 1973. Translated into many languages as Quantum Mechanics, it became one of the most widely used graduate textbooks in the world, known to students simply as the Cohen-Tannoudji.

With Jacques Dupont-Roc and Gilbert Grynberg he wrote two further volumes on quantum electrodynamics and atom-photon interactions, published in English as Photons and Atoms (1989) and Atom-Photon Interactions (1992). His most important papers were collected as Atoms in Electromagnetic Fields (2004). With David Guéry-Odelin he published Advances in Atomic Physics: An Overview (2011), drawn from his Collège de France lectures, and in 2019 he published a memoir, Sous le signe de la lumière: itinéraire d'un physicien dans le monde quantique (Odile Jacob).

In 1958 he married Jacqueline Veyrat, who pursued her own career as a high school physics and chemistry teacher while raising their three children, Alain, Joëlle and Michel. Their eldest son, Alain, died in 1993 of a long illness at the age of 34, a loss Cohen-Tannoudji called a great misfortune; he dedicated his Nobel lecture to Alain's memory. Joëlle Cohen-Tannoudji became a professor at Université Paris-Diderot and Michel Cohen-Tannoudji a researcher at the Institut Pasteur.

His younger brother Gilles Cohen-Tannoudji, born in 1938, is also a physicist. His nephew Denis Cohen-Tannoudji wrote Les Enfants d'Yishmaël (2010), a history of the family's Sephardic origins in North Africa.

He was a strong advocate of fundamental, curiosity-driven research and of teaching modern physics widely. In a 2008 lecture in Hyderabad he said that quantum physics was no longer an abstract theory for specialists and must be included in education and culture.

Described as a humanist, he signed an appeal with other Nobel laureates asking the UN Committee on the Rights of the Child to visit Gedhun Choekyi Nyima, the Tibetan boy recognised by the Dalai Lama as the 11th Panchen Lama. In 2015 he signed the Mainau Declaration on climate change, and in 2016 he was one of more than 100 laureates who signed a letter supporting precision agriculture and genetically modified crops such as golden rice.

Cohen-Tannoudji is regarded as one of the founders of the physics of ultracold atoms. The light shift he discovered as a doctoral student, the dressed atom formalism, Sisyphus cooling and subrecoil cooling are standard tools of modern atomic physics. The Kastler Brossel Laboratory credits his work with spectacular progress in cold atoms, including Bose-Einstein condensation, simulation of many-body quantum systems and atomic clocks.

He was also a builder of people. His students and close collaborators included Serge Haroche, Nobel laureate in 2012, and Alain Aspect, Nobel laureate in 2022, as well as Jean Dalibard, Claude Fabre and Christophe Salomon. Through his textbooks, his Collège de France lectures and summer schools around the world, he helped make atomic physics and quantum optics one of the most creative fields in physics.

His honours included the Paul Langevin Prize (1963), the CNRS Silver Medal (1964), the Jean Ricard Prize (1971), the Thomas Young Medal and Prize of the Institute of Physics (1979), the Ampère Prize of the French Academy of Sciences (1980), the Gay-Lussac Humboldt Prize (1991), the Lilienfeld Prize of the American Physical Society (1992), the Charles Hard Townes Award (1993), the Matteucci Medal, the Harvey Prize of the Technion (1996), the CNRS Gold Medal (1996) and the Nobel Prize in Physics (1997).

He was elected to the French Academy of Sciences in 1981, became a Fellow of the American Physical Society in 1985 and a foreign associate of the US National Academy of Sciences in 1994, and received around 18 honorary doctorates. In the Legion of Honour he rose from knight (1996) to officer (1997), commander (2004), grand officer (2010) and grand cross (2016).

Many of his lectures survive on video, including his 1992 MIT physics seminar on atom-photon interactions, his Collège de France lecture on light as a tool to manipulate atoms, a talk at the Global Young Scientists Summit in Singapore in 2019, the flagship event of the International Day of Light in 2018, and a long series of filmed interviews for the Fondation Hugot du Collège de France covering his childhood, his career and the Nobel Prize.

Claude Cohen-Tannoudji died on Thursday 22 October 2026, aged 93. His family announced his death on Friday 23 October, and Le Monde published an obituary. French Wikipedia, citing Le Monde, gives Paris as the place of death. The cause of death was not made public. The Kastler Brossel Laboratory paid tribute to work that had "permitted spectacular progress in the field of cold atoms", and his nephew Denis Cohen-Tannoudji shared the news of his uncle's death on X.