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Claude Cohen-Tannoudji

(1933 - )

Claude Cohen-Tannoudji is a Jewish French physicist and recipient of the 1997 Nobel Prize in Physics.

Cohen-Tannoudji (born April 1, 1933) was born in Constantine, Algeria. Cohen-Tannoudji moved with his family in 1953 to Paris. From 1953 to 1957, he attended the Ecole Normale Supérieure. Following graduation, Cohen-Tannoudji was enlisted in military service for 28 months because of the Algeria war.

In 1960, he returned to the Ecole Normale laboratory to do a Ph.D. under the supervision of Alfred Kastler and Jean Brossel with a research post at the CNRS (French National Center for Scientific Research). He submitted his Ph.D. in December 1962.

After obtaining his doctorate, Cohen-Tannoudji accepted a professorship at the University of Paris. In 1973, he was appointed professor at the Collège de France.

He is one of most recognized researchers in the field of quantum optics, the best-known part of his work being his part in the development of techniques to cool and trap atoms with light, for which his was awarded the 1997 Nobel Prize in Physics, together with Steven Chu and William Daniel Phillips.

He is also author of a very concise and hence often used text book, "Quantum Mechanics", which originated from his teaching experiences at the University of Paris. This book was written in collaboration with Franck Laloë and Bernard Diu.

The following press release from the Royal Swedish Academy of Sciences describes Cohen-Tannoudji's work:

At room temperature the atoms and molecules of which the air consists move in different directions at a speed of about 4,000 km/hr. It is hard to study these atoms and molecules because they disappear all too quickly from the area being observed. By lowering the temperature one can reduce the speed, but the problem is that when gases are cooled down they normally first condense into liquids and then freeze into a solid form. In liquids and solid bodies, study is made more difficult by the fact that single atoms and molecules get too close to one another. If, however, the process takes place in a vacuum the density can be kept low enough to avoid condensation and freezing. But even a temperature as low as -270°C involves speeds of about 400 km/hr. Only as one approaches absolute zero (-273°C) does the speed fall greatly. When the temperature is one-millionth of a degree from this point (termed 1 µK, microkelvin) free hydrogen atoms, for example, move at speeds of less than 1 km/hr (= 25 cm/s).

Steven Chu, Claude Cohen-Tannoudji, and William D. Phillips have developed methods of using laser light to cool gases to the µK temperature range and keeping the chilled atoms floating or captured in different kinds of "atom traps". The laser light functions as a thick liquid, dubbed optical molasses, in which the atoms are slowed down. Individual atoms can be studied there with very great accuracy and their inner structure can be determined. As more and more atoms are captured in the same volume a thin gas forms, and its properties can be studied in detail. The new methods of investigation that the Nobel Laureates have developed have contributed greatly to increasing our knowledge of the interplay between radiation and matter. In particular, they have opened the way to a deeper understanding of the quantum-physical behaviour of gases at low temperatures. The methods may lead to the design of more precise atomic clocks for use in, e.g., space navigation and accurate determination of position. A start has also been made on the design of atomic interferometers with which, e.g., very precise measurements of gravitational forces can be made, and atomic lasers, which may be used in the future to manufacture very small electronic components.

Sources: Wikipedia,, Nobel Prize Autobiography