Prof. Dr. Andreas Hemmerich

What we did in short:

We used samples of atoms cooled to temperatures below hundred nanokelvin, such that their motion is governed by quantum mechanics, in order to either prepare minimal models of natural electronic many-body systems or to form entirely new types of many-body scenarios, which do not exist in electronic matter. Both strategies are motivated by the desire to increase our understanding of quantum many-body physics. Our research covered topics such as optical lattices with orbital degrees of freedom, topological optical lattices, ultracold atoms in optical high finesse cavities. We also employed cold atomic samples to explore new concepts for quantum metrology such as superradiant lasing.

And in a few more words:

The essence of quantum many-body physics is nicely captured by the punch line "More is Different". In fact, it is a fascinating intellectual and technically relevant venture to understand how collections of seemingly simple elementary constituents, under the reign of physical principles such as degeneracies, interactions, and symmetries, collude to bring about the often unexpected collective phenomena of condensed matter. This is all the more true, when we consider the dynamics of such systems.

The vast complexity of natural many-body systems often led us to seek ab initio tractable minimal quantum models, which can capture a few isolated phenomena of interest, while excluding the superimposed jungle of secondary structure that would impede a clear understanding. This is where quantum gases come into play. Quantum gas systems have synthetic model character, in the sense that they follow a bottom-up philosophy, where elementary ingredients are strategically combined to provide the minimal input required to simulate some specific feature of a natural electronic many-body system. Alternatively, quantum gas systems allow one to form entirely new types of many-body scenarios, which do not exist in electronic matter but nevertheless can be extremely helpful to increase our intuition and knowledge of many-body physics in general. A typical example of a quantum gas system is what one calls an optical lattice, where neutral atoms at temperatures of few ten nanokelvin are confined in periodic potentials created by the interference of several laser beams, thus forming crystals of atoms bound by light. If fermionic atoms are employed, they can serve to simulate the electrons in natural crystalline matter. With bosonic atoms crystalline quantum matter can be formed, that has no counterpart in electronic condensed matter.

Our special focus was to explore the interaction of quantum gas systems with light, often in a dynamical regime far from thermal equilibrium. Our research covered topics such as optical lattices with orbital degrees of freedom, topological optical lattices, ultracold atoms in optical high finesse cavities, and superradiant lasing in optical atomic clocks.