Quantum dynamics of strongly correlated RbCs dipolar gases

Ultracold atoms and molecules confined to lattice potentials offer myriad possibilities for the controlled preparation and study of strongly correlated quantum many-body systems. For atoms, milestones in the field have been the experimental realization of the Hubbard model of condensed matter physics and the observation of the superfluid-to-Mott-insulator phase transition for systems with local contact interactions. Molecules have the potential to greatly broaden the spectrum of strongly correlated quantum systems that can be investigated. In particular, dipolar molecules with their long-range and orientation dependent electric dipole-dipole interaction provide new opportunities to probe e.g. novel forms of superfluidity and interesting many-body ground states (such as dipolar crystals, supersolids, fractional Mott insulators, quantum magnets,) in conjunction with novel quantum phase transitions, and in general non-equilibrium quantum many-body dynamics. This project is aimed at studying the dynamics of ultracold RbCs dipolar bosons confined to one- and two-dimensional geometry and lattice potentials. The RbCs dipoles, initially prepared from atom pairs located at individual sites of an optical lattice at high filling fraction, will be studied in the regimes of frozen spins (i.e. fixed spatial location in the lattice) and in the regime of mobile dipoles. We will explore to what extent one can realize novel many-body spin models, with possible applications to the field of quantum simulation, and study the stability, dynamics and relaxation processes for many-body systems composed of quantum dipoles confined to low-dimensional geometry. In particular, our project aims at testing in experiments the dynamical processes as allowed by the extended Hubbard model, i.e. the Hubbard model augmented by terms modeling off- site interaction terms. The project is based on an existing Rb-Cs quantum gas mixture apparatus (set up over several years within the Austrian SFB FoQuS, funded by the FWF) for which we have implemented efficient ground-state transfer of ultracold RbCs molecules into a specific hyperfine sublevel of the RbCs ground-state molecule and for which we have demonstrated high molecular filling fraction in a three-dimensional lattice potential.

The aim of the project is to develop an experimental platform to study the quantum dynamics of dipolar many-body quantum systems in experiments based on ultracold molecules. This line of research has attracted a lot of interest in recent years, and many research groups around the world are working in this area. Dipolar quantum gases significantly expand the range of possibilities in the field of ultracold quantum gases, e.g. by the possibility of creating new states of matter such as a supersolid state. In this project we focused on the generation of quantum gases from RbCs molecules. Much of this work is still work in progress. The ultra-cold molecules are to be composed of atoms in the nanokelvin temperature range. For this purpose, among other things, strong light forces are used to hold the atoms and molecules. We have succeeded in identifying so-called confinement-induced resonances, on which strongly-stored atoms couple to molecular states. The existence of such confinement resonances had previously only been predicted for one-dimensional systems, and we were able to find out that nonlinear processes with strong three-dimensional confinement in e.g. an optical lattice cause such resonances. Furthermore, we were able to develop a generation pathway that should make it possible to prepare the RbCs molecules with high efficiency and high phase-space density in the ground state. This path has already been followed in a collaboration with experimental colleagues from Durham, UK. In order to make the generation of molecules and the experiments with the molecular quantum gases as simple as possible, significant conversion work was carried out on the existing apparatus and the laser system. This work is nearing completion at the end of the project. The scientific work will of course be continued as part of another project.