Magnetic evaporative cooling
Encyclopedia
Magnetic evaporative cooling is a technique for lowering the temperature
of a group of atom
s. 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.
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 170 nanokelvins for rubidium
atoms.
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 Randall G. 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.
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
of a group of atom
Atom
The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...
s. The process uses a magnetic field to put atoms in a magnetic trap
Magnetic trap (atoms)
A magnetic trap uses a magnetic gradient to trap neutral particles with a magnetic moment. Although such traps have been employed for many purposes in physics research, they are best known as the last stage in cooling atoms to achieve Bose-Einstein condensation...
, 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.
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 170 nanokelvins for rubidium
Rubidium
Rubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group. Its atomic mass is 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other elements in group 1, such as very rapid...
atoms.
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 Randall G. Hulet for lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
. 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.
See also
- ThermodynamicsThermodynamicsThermodynamics is a physical science that studies the effects on material bodies, and on radiation in regions of space, of transfer of heat and of work done on or by the bodies or radiation...
- Quantum mechanicsQuantum mechanicsQuantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...
- Statistical mechanicsStatistical mechanicsStatistical mechanics or statistical thermodynamicsThe terms statistical mechanics and statistical thermodynamics are used interchangeably...
- Superconductor
External links
- C. E. Wieman and E. A. Cornell, Bose-Einstein condensate.