Winning the Nobel prize for physics is like being hit by a tornado, according to one of this year's laureates. "I just wish it would stop so that I could go back to work," says Claude Cohen-Tannoudji of the Collège de France and the Ecole Normale Supérieure in Paris. He shares the 1997 prize with Steve Chu of Stanford University in California and Bill Phillips of the National Institute of Standards and Technology in Gaithersburg, Maryland, for developing techniques to cool and trap atoms at extremely low temperatures using lasers.
The past few years have seen remarkable developments in the ability to control atomic motion by optical techniques. Among the key tools that have been developed for this purpose are the techniques of laser cooling, the significance of which was recognized by the award of the 1997 Nobel Prize in Physics to Steven Chu, Claude Cohen-Tannoudji, and William Phillips. These techniques have made it possible to cool atoms to temperatures lower than have been produced in any other physical system - around 10(-8) degrees Kelvin above absolute zero - and to confine those in traps for extended periods of observation.
When the Nobel Prize for Physics was awarded to Claude Cohen-Tannoudji, William D. Philipps and Steven Chu in 1997 for the development of methods for cooling and trapping atoms using lasers, this was the reward for two decades of investigations not only touching upon the fundamental aspects of the light–matter interaction, but also leading to a range of applications. On the theoretical level, the advent of this field of research in the late 1970s stimulated the development of various theoretical methods for describing the radiative forces by which light affects the motion of atoms. On the experimental level, judicious use of the radiative forces exerted by lasers made it possible to obtain a drastic reduction of atomic velocities – in other words, to cool an atomic vapour. These advances were characterized by a remarkable cross-fertilization of theoretical and experimental innovations. It was not long before applications began to appear in the field of high-resolution spectroscopy, since ultracold, i.e. slow, atoms can be observed for longer periods, and this allows greater accuracy when measuring atomic resonance frequencies than could be obtained for atoms at room temperature. Based on such resonances, the most accurate clocks in the world use laser-cooled atoms or ions. Atom interferometry is another application of laser manipulation of atoms, which can be applied to measure inertial effects, due for example to the rotation of the Earth or the motion of a vehicle, with an accuracy that already exceeds traditional methods.
Abstract William Phillips of the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland, shared the 1997 Nobel Prize in physics for his work in developing laser methods for cooling and trapping atoms. Interactions between the light field and the atoms create what is dubbed an ‘optical molasses’ that slows the atoms down, thereby reducing their temperature to within a fraction of a degree of absolute zero. These techniques allow atoms to be studied with great precision, for example measuring their resonant frequencies for light absorption very accurately, so that these frequencies may supply very stable timing standards for atomic clocks. Besides applications in metrology, such cooling methods can also be used to study new fundamental physics. The 1997 Nobel award was widely considered to be a response to the first observation in 1995 of pure Bose–Einstein condensation (BEC), in which a collection of bosonic atoms all occupy a single quantum state. This quantum-mechanical effect only becomes possible at very low temperatures, and the team that achieved it, working at JILA operated jointly by the University of Colorado and NIST, used the techniques devised by Phillips and others. Since then, cold-atom physics has branched in many directions, among them being attempts to make a quantum computer (which would use logic operations based on quantum rules) from ultracold trapped atoms and ions. ‘National Science Review’ spoke with Phillips about the development and future potential of the field.
Forty years ago, twenty years after the discovery of the laser, physicists were developing laser cooling methods for ions trapped in electromagnetic fields.From the 1980s onwards, these techniques were refined and extended to atoms, thanks to the audacity and inventiveness of a generation of pioneering researchers.Actually, it was necessary to succeed simultaneously in trapping and cooling samples of atomic gases in a vacuum at a distance from any wall.Spectacular results followed and extraordinarily low temperatures were quickly reached, very close to absolute zero.The field of "cold atoms" was born, rewarded by successive Nobel prizes, first of which was awarded in 1997 to William D. Phillips, Steven Chu and Claude Cohen-Tannoudji, last in 2022 to Alain Aspect.Gaseous samples of a few thousand to a few billion atoms can be prepared at a few millionths of a degree above absolute zero, which means that the particles move at extremely low speed, of the order of centimetres per second.At these extreme temperatures, the behaviour of matter changes and its properties can only be described using quantum mechanics and the wave properties of particles.New physical phenomena have been discovered and innovations have followed the theoretical and experimental progress of the research.Initially imagined as a wonderful method for perfecting atomic physics, cold atoms have gradually proved to be powerful tools for research in cross-cutting fields of physics, such as condensed matter and even high-energy physics.These atoms are now referred to as 'quantum gases' at such low temperatures that their collective behaviour is modified by the laws of quantum mechanics.
Abstract Mit der Verleihung des diesjährigen Nobelpreises für Physik an Steven Chu (Stanford University), Claude Cohen‐Tannoudji (ENS, Paris) und William D. Phillips (NIST, Gaithersburg) würdigt die Schwedische Akademie der Wissenschaften die bahnbrechenden Arbeiten zum Kühlen und Speichern von Atomen mit Laserlicht. Die seit etwa 15 Jahren zur Verfügung stehenden Methoden zur gezielten Manipulation der äußeren Freiheitsgrade von Atomen durch die Einstrahlung von Lichtfeldern haben neue, weitreichende Entwicklungen in der Atomphysik sowie der Quanten‐ und Atomoptik stimuliert. Neben dem besseren Verständnis der Wechselwirkung von Strahlung mit Materie haben die Arbeiten zahlreiche Anwendungsfelder, z. B. Hochpräzisionsspektroskopie, Atomuhren, Atominterferometrie, Atomlithographie, Stoßphysik und die Wechselwirkung von Atomen mit Oberflächen, erheblich erweitert bzw. erst erschlossen.