Atomic and molecular quantum gases

Quantum behaviour determines the physical properties of matter at extremely low temperatures. For example, the intriguing phenomena of superfluidity and superconductivity (the frictionless transport of particle streams and electrical currents) result from condensation in a many-particle quantum state. Phenomena of this kind are often very complex and poorly understood, but they have great potential for applications, with one classic example being the zero-resistance conductivity of electrical currents. At temperatures of a few billionths of a degree above absolute zero, ultracold gases offer a unique perspective on the quantum world of many-particle systems. Such systems are prepared in electromagnetic traps in a vacuum chamber using laser and evaporative cooling and can be controlled specifically and examined with high accuracy using a laser. In this way, it is possible to realise near-perfect model systems in a laboratory setting in order to better understand the physics of complex quantum systems. A small cloud of several hundred thousand fermionic lithium atoms can, for example, simulate the behaviour of a neutron star or of matter in the early development stages of the universe. In the last 20 years, intensive research has been conducted on methods for cooling gases made of atoms. Bose- Einstein condensates, in which all particles are in the same quantum state, were developed approximately ten years ago. Especially in the last two years, this field of research has seen dramatic advances, as atoms in ultracold gases can now be combined to form molecules, weakly bound pairs or even large quantum objects. These advances have flung the door open to entirely new applications: Chemistry at absolute zero now holds the potential to allow synthesis of more complex objects in well-defined quantum states whose internal and external degrees of freedom can be controlled perfectly. One topic of special interest is fermionic atoms, which, as particles with odd half-integer spin, correspond to elementary building blocks of matter such as electrons, protons and neutrons. According to the Pauli Exclusion Principle, such particles cannot occupy the same quantum state simultaneously. However, they can form pairs which behave like bosons (i.e. particles with integer spin) and can thus condense into a macroscopic quantum state nonetheless. This pairing mechanism is responsible for superconductivity. Therefore, scientists hope to use experiments with ultracold Fermi gases to generate new insights on high-temperature superconductivity, that is, the ability of certain materials to enable zero-resistance current transport at relatively high temperatures. The Wittgenstein Award will enable Rudolf Grimm to realise novel ultracold model systems in an experimental setting, to examine their elementary interactions, and thus to gain new insights into the general behaviour of complex quantum systems.