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Cold Atoms & Molecules

Precise control over the internal quantum states as well as the motional state of microscopic particles is the crucial driving force for understanding and making use of the quantum world. This allows for example to manipulate and store quantum information in atoms, ions and molecules. In small samples the control has reached the single atom level. This further allows for the precise localization of atoms to a fraction of optical wavelengths necessary for controlled interactions with classical and even quantized optical fields of low photon number. For ensembles with larger particle numbers control over many body quantum phases can be realized like Bose-Einstein condensates, strongly interacting superfluid fermions, or various phases in periodic potentials of optical lattices filled with atoms, polar molecules, or Rydberg atoms.

We develop experimental quantum technologies to enhance this precise control in a broad range of experimental approaches to access new physical areas.

A significant effort in our experimental research is thus dedicated to prepare individual particles or ensembles of them close to their motional ground state

- or in simple terms, to cool them. Typical temperatures achieved are a few 10 microkelvin by standard laser cooling and down to a few 10 nanokelvin by evaporative cooling that allows to cross quantum phase transitions. We advance cooling techniques by exploring laser cooling of individual atoms, Raman sideband cooling, laser cooling on narrow optical transitions, of evaporative cooling of mixtures of multiple species. Further controlling the motional state of the particles and facilitation of the cooling techniques is achieved by a variety of trapping methods like magneto-optical traps, magnetic traps, optical traps and ion traps. We have to develop and carefully adapt experimental configurations to produce cold samples of the different species under study. One unique advantage is that we can design and even dynamically change the trapping parameters and study the same quantum system in various dimensions (1D to 3D).

Control over the internal states like electronic states, magnetic spins in external magnetic fields, or vibration and rotational levels in molecules can be used on one hand to store quantum information and study entanglement. On the other hand it can be used to create rich many body systems like e.g. various types of spin lattice models. In systems with neutral atoms and molecules we have control over the interaction strength between the particles as an experimental tool to study many body systems, or process quantum information by controlled interactions.

This overall toolbox of quantum technologies allows us to manipulate quantum systems to a degree that is typically not possible in condensed matte or solid state physics.