Magneto-optical trap in the context of "Magnetic trap (atoms)"

In condensed matter physics, an ultracold atom is an atom with a temperature near absolute zero. At such temperatures, an atom's quantum-mechanical properties become important, especially through what's known as a "superfluid", such as Superfluid Helium 4.

To reach such low temperatures, a combination of several techniques typically has to be used. First, atoms are trapped and pre-cooled via laser cooling in a magneto-optical trap. To reach the lowest possible temperature, further cooling is performed using evaporative cooling in a magnetic or optical trap. Several Nobel prizes in physics are related to the development of the techniques to manipulate quantum properties of individual atoms (e.g. 1989, 1996, 1997, 2001, 2005, 2012, 2018).

Laser cooling includes several techniques where atoms, molecules, and small mechanical systems are cooled with laser light. The directed energy of lasers is often associated with heating materials, e.g. laser cutting, so it can be counterintuitive that laser cooling often results in sample temperatures approaching absolute zero. It is routinely used in atomic physics experiments where the laser-cooled atoms are manipulated and measured, or in technologies, such as atom-based quantum computing architectures.

Laser cooling reduces the random motion of particles or the random vibrations of mechanical systems. For atoms and molecules this reduces Doppler shifts in spectroscopy, allowing for high precision measurements and instruments such as optical clocks. The reduction in thermal energy also allows for efficient loading of atoms and molecules into traps where they can be used in experiments or atom-based devices for longer periods of time.