Quantum Dynamics of Strongly Correlated RbCs Dipolar Quantum 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 increase 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 (presently funded as a SFB project) for which we have implemented efficient ground-state transfer of ultracold RbCs molecules into a specific hyperfine sublevel of the RbCs ground-state molecule.

The field of ultracold quantum gases has seen a spectacular development over the course of the past 25 years. A highlight was the first formation of a Bose-Einstein condensate (BEC) with ultracold atoms in 1995, a feat that was acknowledged by the Nobel Prize to Cornell, Ketterle, and Wieman in 2001 and that has led to many spectacular research results since then. When confined to periodic lattice potentials, ultracold atoms and molecules 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 increase 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- (1D) and two-dimensional (2D) 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. An open question is whether it will be possible to put ground-state molecules into the state of a BEC. For preparing the molecules in the regime of quantum degeneracy, an elaborate preparation procedure is needed. In the past years, we have dedicated most of our time to improving this procedure and to understand in detail some of the relevant processes. For example, we have, for the first time, detected confinement-induced resonances in 0D confinement. These resonances appear when the length scales of confinement and of scattering start to compete, and these have previously been only seen in 1D and 2 D confinement. We have investigated into the phenomenon of superfluid transport. When we transport atoms across 200 lattice sites of an optical lattice, it is crucial not to break the superfluid speed limit. In fact, samples that are not superfluid are not transported at all. In addition, we have completely rebuilt our laser system needed for laser cooling in order to simplify the setup, thereby reducing the number of laser from about 20 to 12.