Magnetic evaporative cooling is a technique for lowering the temperature of a group of atoms. The process uses a magnetic field to put atoms in a magnetic trap, a flask-shaped magnetic field. Collisions mean that over time, individual atoms will become much more energetic than the others, and they will escape the trap, removing energy from the system and reducing the temperature of the group remaining. This process, where particles by collision surmount a barrier, is similar to the familiar process by which standing water becomes water vapor. Fig. ... “Atomic” redirects here. ... A magnetic trap uses a magnetic gradient in order to trap neutral particles with a magnetic moment. ...

A way to visualize this is to take a bowl and fill it almost all the way up with popcorn. Then shake the bowl enough so that the bouncing isn't enough to spill over the side. Every so often one of the popped corns will jump out, "evaporating" from the bowl.

This technique was developed to study the Bose-Einstein condensate, an exotic state of matter in which multiple atoms enter the same quantum state. This condensation only happens at very low temperatures: around 50 nanokelvins for rubidium atoms. A Bose–Einstein condensate is a phase of matter formed by bosons cooled to temperatures very near to absolute zero (0 kelvins or -273. ... A quantum state is any possible state in which a quantum mechanical system can be. ... The Kelvin scale is a thermodynamic (absolute) temperature scale where absolute zero—the lowest possible temperature where nothing could be colder and no heat energy remains in a substance—is defined as zero kelvin (0 K). ... General Name, Symbol, Number rubidium, Rb, 37 Chemical series alkali metals Group, Period, Block 1, 5, s Appearance grey white Atomic mass 85. ...

The use of kinetic evaporation was pioneered in 1995, first by Eric A. Cornell and Carl E. Wieman for rubidium, and then by the group of Randy Hulet for lithium. Since then the technique has been improved upon, notably by Bouyer's team at Groupe d'Optique Atomique Laboratoire at the Charles Fabry Optical Institute. General Name, Symbol, Number lithium, Li, 3 Chemical series alkali metals Group, Period, Block 1, 2, s Appearance silvery white/grey Atomic mass 6. ...

See also

• Thermodynamics
• Quantum mechanics
• Statistical mechanics
• Superconductor

Thermodynamics (from the Greek thermos meaning heat and dynamics meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ... Fig. ... Statistical mechanics is the application of probability theory, which includes mathematical tools for dealing with large populations, to the field of mechanics, which is concerned with the motion of particles or objects when subjected to a force. ... Superconductivity is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of electrical resistance and the damping of the interior magnetic field (the Meissner effect. ...

References

• M. H. Anderson, J. R. Ensher, M. R. Matthews, C. E. Wieman and E. A. Cornell, Observations of Bose-Einstein Condensation in a Dilute Atomic Vapor, Science, 269:198–201, July 14, 1995.
• J. J. Tollett, C. C. Bradley, C. A. Sackett, and R. G. Hulet, Permanent magnet trap for cold atoms, Phys. Rev. A 51, R22, 1995.
• Bouyer et al, RF-induced evaporative cooling and BEC in a high magnetic field, physics/0003050, 2000.

Science is the journal of the American Association for the Advancement of Science (AAAS). ... July 14 is the 195th day (196th in leap years) of the year in the Gregorian Calendar, with 170 days remaining. ... 1995 (MCMXCV) was a common year starting on Sunday of the Gregorian calendar. ...

External links

• C. E. Wieman and E. A. Cornell, Bose-Einstein condensate.