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French physicist Claude Cohen-Tannoudji shared the 1997 Nobel Prize in physics with two other physicists. All three physicists were recognized for their individual work in cooling and trapping atoms
Claude Cohen-Tannoudji, born in 1933, French physicist and Nobel laureate. Cohen-Tannoudji pioneered research into cooling, slowing, and trapping atoms—one of the basic building blocks of matter—with special beams of light called lasers (see Particle Trap). The techniques Cohen-Tannoudji and others developed led to significant advancements in the study and manipulation of atoms, resulting in many applications. These applications include more accurate atomic clocks and more precise devices for measuring gravity. He shared the 1997 Nobel Prize for physics with two American scientists who were also successful in slowing atoms, Steven Chu and William D. Philips. The three didn’t work side by side; yet each contributed to and built upon the work of the other two.
Born in Constantine, Algeria, Cohen-Tannoudji earned his undergraduate degree in 1957 and his Ph.D. degree in 1962 in physics from École Normale Supérieure (ENS) in Paris, France. As a student at ENS he worked under the direction of French physicist Alfred Kastler, who won the Nobel Prize in physics in 1966, and Jean Brossel, another noted French physicist. Cohen-Tannoudji remained a researcher at ENS throughout his career. He was instrumental in the creation of a research center devoted to atomic physics and optics. The center is named the Kastler-Brossel Laboratory, after his two professors.
Cohen-Tannoudji joined the Centre National de la Recherche Scientifique (CNRS) in 1960. In 1973, while still associated with CNRS, he began a lengthy stint as chair of atomic and molecular physics at the Collége de France in Paris.
As a student, researcher, and professor, Cohen-Tannoudji became an expert in the field of slowing atoms. At room temperature, atoms move at speeds of about 4000 km/h (about 2500 mph), too fast for scientists to study them thoroughly. Heat results from atomic motion, so slowing atoms down lowers their temperature. Cohen-Tannoudji was among the first to propose using lasers to slow down atoms. The concept involves bombarding the atoms with laser light. Packets of light wave energy called photons strike the atoms in a way that is roughly the same as raindrops hitting a beach ball. Even though the photons have no mass, they move fast enough (at the speed of light) to produce enough momentum to slow the atoms with their impacts.
In 1985 Steven Chu and his team cooled atoms to 240 millionths of a Celsius degree (430 millionths of a Fahrenheit degree) above absolute zero (-273.15° C, or -459.67° F), which slowed atoms to about 0.5 km/h (0.3 mph). By 1988 William D. Philips and his research team had cooled atoms to 40 millionths of a Celsius degree (70 millionths of a Fahrenheit degree) above absolute zero, which was below the temperature that was believed to be theoretically possible at the time. In 1995 Cohen-Tannoudji and his team achieved a temperature of 0.2 millionths of a Celsius degree (0.4 millionths of a Fahrenheit degree) above absolute zero. Through his career Cohen-Tannoudji developed several cooling mechanisms used to trap atoms.
Manipulating atoms and studying them more closely allows scientists to improve many areas of technology. In an atomic clock, the more control the mechanism has over the atoms that it uses to keep track of time, the more accurate it can be. Increasingly accurate atomic clocks improve space navigation and global positioning systems that rely on the clocks. Trapped atoms are also useful in measuring the force of gravity of a particular spot on the earth. Changes in the gravitational field of the earth from place to place indicate changes in the density of the earth, which can lead scientists to oil and other valuable deposits within the earth. The ability to control atoms also raises the possibility of using atoms to etch electronic circuits. This would increase the circuits’ capabilities by making the circuits finer, and each area of circuit board would be able to hold more circuits.
In 1996 Cohen-Tannoudji won CNRS’s gold medal. In 1997, along with former students Jacques Dupont-Roc and Gilbert Grynberg, he wrote the book Introduction to Quantum Electrodynamics.