This research program investigates the intriguing physics of nonlinear quantum hydrodynamics, using ultracold atomic gases such as Bose-Einstein condensates (BECs) as well-controlled model systems. In the experiments, clouds of atoms are cooled to temperatures near zero Kelvin, where their dynamics strongly deviate from the dynamics of classical particles and matter-wave behavior emerges. The wave nature of the atoms in this extreme regime leads to fluid-like behavior described by a hydrodynamic model. Capitalizing on the most recent advances and developments, the program provides much needed benchmark results for the development of a deep understanding of nonlinear quantum hydrodynamics. Topics include multi-soliton dynamics, binary quantum turbulence, multicomponent counterflow and Raman-dressed BECs. The experiments go beyond the realm of existing theories and provide strong stimuli for the development of a precise theoretical picture that is needed for future applications.
The results of this research program are relevant in a broad context. Strong parallels exist between BEC hydrodynamics and the technologically important propagation of light through optical fibers. For future telecommunication applications using solitons of light as bits of information transmitted through optical fibers, a precise understanding of multi-soliton dynamics analogous to the one found in BECs will be important. Second, Raman-dressed BECs exhibit spin-orbit coupling which plays a prominent role in advanced condensed matter systems, e.g. for the spin quantum Hall effect, topological insulators, and engineering of Majorana fermions with applications to topological quantum computation. Furthermore, the research program provides new insight into quantum turbulence and thus aids the development of a better understanding of classical turbulence, which is often quoted as the most important unsolved problem in classical physics. This research program also plays an important role for the education of students. It allows students at all levels to gain experience with state-of-the-art instruments and techniques while they perform experiments addressing some of the most pressing open questions in quantum hydrodynamics. The students will be well prepared for future careers in industry and academia.
