Subproject E2
Ultracold Bosonic and Fermionic Atoms in Driven Optical Lattices
Dr. Christof Weitenberg, Prof. Dr. Klaus Sengstock
Topological phases from Quantum Hall systems to fractional Chern Insulators are a fascinating field in solid-state physics, going beyond the Landau paradigm of broken symmetries. Recently there has been tremendous progress in engineering artificial gauge fields and topological bands in ultracold atom systems, e.g. by laser-assisted tunneling or lattice driving. With their well-controlled preparation and detection techniques, cold atom systems open a new approach to these topological phases. The tunable interaction strength promises new insights into the interplay of gauge fields and interactions, which is still largely unexplored. Moreover, having large-spin systems or Bose-Fermi mixtures at hand, one can study settings beyond the scope of solid-state systems.
In this project, we want to refine the established technique of lattice driving to engineer artificial gauge fields and topological band structures and move on to study interacting phases in these bands. Using our experimental apparatus of 40K and 87Rb, we will study both fermionic and bosonic phases as well as Bose-Fermi mixtures. Together with the theory projects of this Research Unit, we want to identify suitable experimental signatures and detection tools such as Bragg spectroscopy and then explore the ensuing rich phase diagrams. We plan to investigate the excitation and heating mechanisms intrinsic to the lattice shaking in interacting systems. This will allow for general further insight into Floquet engineered systems.
Moreover, an important goal is to engineer non-Abelian gauge fields both as external fields and induced by interband spin-changing collisions in hexagonal lattices. Finally, the project aims to use quenches between different topologies in order to access the current pattern in the topological phases and to study non-equilibrium dynamics in topological systems.
Berry curvature of the lowest Floquet band in a driven hexagonal lattice. The distribution of Berry curvature can be engineered by suitable lattice shaking and detected from the quench dynamics after projection onto flat bands. This powerful technique opens up many prospects for studying dynamics, interacting systems or non-abelian gauge fields [adapted from: Fläschner et al. Science 352, 1091 (2016)].