Sympathetic cooling

Sympathetic cooling is a technique of quantum optics, the particles are used in a type (1) in order to cool the particles of another type (2). The particles of the type (1) act as a heat bath for particles of type ( 2), the temperature was slowly up to the level of the particles ( 1) is lowered. The coupling occurs via collisions between the particles, or for example when ions by Coulomb interaction. The low-energy particles of type (1 ) is obtained by the energy of the particles to be cooled (2).

The sympathetic cooling can be compared on an ice bath vividly with the cooling of a food ( eg some dessert creams).

By sympathetic cooling, the application of laser cooling is especially extended to those atoms that are not directly cooled. In this laser cooling of neutral atoms by scattering of photons ( from different directions ) is lowered the speed of the atoms. This, however, a so-called closed transition is necessary, that is, it must be possible to raise the atom with a laser from a ground state to a specific excited state from which it then falls back into the same ground state. The probability for the atom to leave this cycle into a dark state, so must not be too large. If not available, a closed transition for one to be cooled atom, may be resorted to the method of the sympathetic cooling by introducing a second atom in the experiment, which can be cool well with lasers and which then serves as a heat bath for the first atom type.

Sympathetic cooling was first demonstrated for ions and later also for atoms. With the similar method to fast electron cooling of antiprotons at CERN were cooled by cold electrons.