General description

The research field of ultracold atoms has become more and more important in the last few decades, with the technological development in this field also advancing more and more. In 1997, the Nobel Prize in Physics was awarded to Steven Chu, Claude Cohen-Tannoudji and William Phillips for the method they developed for laser cooling of atoms, on which this advanced practical experiment is also based. Ultracold temperatures means that temperatures close to absolute zero are reached. In this regime, quantum properties dominate compared to classical or thermal properties of matter. Among other things, magnetic fields and laser beams can be used to shape potentials for atoms. This makes these quantum systems easily controllable. The atoms can be manipulated in motion, in their quantum state and in their interaction. Therefore, they form a perfect model system that allows complex quantum systems to be explored.  The trapping and cooling of atoms in a magneto-optical trap (MOT) is an elementary technique used in many laboratories today. In ultracold atom experiments, the magneto-optical trap is usually used as a precursor to cooling and trapping, where the atoms are cooled to temperatures in the microkelvin range. Subsequently, the atoms are usually transferred to another trap. There, the atoms are cooled by evaporative cooling to even lower temperatures, down to the nano-Kelvin range. In comparison, liquid nitrogen only achieves a temperature of 77 K. Here, cooling means that the velocity of the atoms is reduced to the nano-Kelvin range. Cooling here means that the speed of the particles' movement is reduced. It is only through magneto-optical traps that phenomena such as Bose-Einstein condensation in atomic gases become experimentally accessible.