Collective Quantum Dynamics of Multi-level Atoms in Cavities

Quantum properties such as discrete energy states of atoms, superpositions of these states and the entanglement of multiple particles form the basis for new quantum technologies. A particularly relevant example of such a technology is the atomic clock, the most accurate measuring device ever developed by humans. It uses two states in an atom whose energies, and therefore also frequencies, are known very precisely. A laser now attempts to create a superposition between these states. However, this only works if the frequency of the laser corresponds exactly to that of the atom. Thus, the laser frequency can be calibrated to that of the atom. A stable frequency reference in turn automatically leads to accurate time measurement, which is relevant for many applications such as GPS. The accuracy of such an atomic clock can be significantly improved by entangling several atoms with each other, i.e. they are in a collective state that cannot be described by the states of the individual atoms. However, creating such entangled states is generally a difficult task. One possibility is to place the atoms between two mirrors. As a result, the light particles (photons) emitted by the atoms are reflected several times by the mirrors and thus act back on the atoms. In this way, so-called squeezed and subradiant entangled states can be generated. In this project, we are working closely with experimentalists to develop new, improved protocols for generating such entangled states. To this end, we are investigating methods that use multiple atomic energy states. This makes the theoretical description more complicated, however, it opens up new possibilities. With the successful implementation of the project, new quantum-based measurement methods and technologies will be developed using multi- level atoms between mirrors. Among other things, these will enable more precise measurements of fundamental physical phenomena, as well as practical applications such as time measurement.