Ultracold Atoms and Molecules: From Defect Dynamics to Quantum Glass

With the present application I propose research in the field of theoretical many-body and condensed matter physics with cold atoms and molecules in reduced dimensionality using computer simulations. The project is of strong interdisciplinary nature combining methods from soft condensed matter physics with current challenges in atomic, molecular, and optical physics (AMO). With the rapid experimental development of the last decade in AMO physics it is now possible to study many-body quantum phenomena with ultracold atoms. The considerable interest in this approach stems from the large degree of control over the Hamiltonian with external fields. While previously, systems with short range interaction have been studied extensively the current experimental challenges are the realization of long range strongly correlated quantum gases and to go beyond the static frozen gas regime to also study the dynamics. Candidates for possible realizations are based on Rydberg atoms and dipolar molecules in reduced geometry. With the present application I propose the study of dynamical aspects of ultracold atomic and molecular crystals. The dynamics and interaction of vacancies and interstitials is crucial for many classical - and quantum phases in two-dimensional crystals. The connection between supersolidity and the vacancy interaction in atomic and molecular crystals is an open question. Preliminary studies let me propose a method that allows one to tune the interaction between defects in the presence of an optical lattice. The goal is to understand the dynamics of these defects with variable interaction and the microscopic origins of supersolidity in this system. Droplet-crystals are a novel phase that was found in ultrasoft colloidal system and recently in two-dimensional systems of Rydberg dressed atoms. In this phase, particles form clusters, which crystallize at high densities. In the ultracold regime this system becomes supersolid. The dynamics of defects and the microscopic origin of supersolidity from this phase is an open question. Preliminary calculations show that in the relevant regime defects are found in two different modes: as interstitials and vacancies, and as novel droplet-defects with completely different static and dynamical properties. The far-reaching goal is to use these novel defects to study the origin of supersolidity in the droplet forming crystals. In dipolar bilayer systems, the anisotropic interaction between particles can lead to the formation of inter-layer pairs. Preliminary studies show that these pairs with their larger effective interaction act as defects that can lead to dynamical heterogeneity and suppress crystallization. I propose the study of a possible glass phase in bilayer systems with the goal to propose an experiment that allows one to study the quantum glass transition with Rydberg dressed atoms and dipolar molecules.

The FWF financed project Ultracold Atoms and Molecules: From Defect Dynamics to Quantum Glass aimed at understanding many-body phenomena that are usually encountered in soft matter systems in the quantum regime. This includes the physics of glasses, liquid crystals and defects in colloidal systems. The focus of the research was fundamental research of the quantum analogs of these effects as well as the concrete implementation in current experiments with ultracold atoms, moleculs, ions and nano-particles in optical cavities. Highlights of the research include a proposal for structural quantum glasses in bilayers of dipolar quantum crystals, tunable liquid crystals from nano-dumbbells in optical cavities, the proposal of a quantum-hexatic phase in dipolar crystals and a model for crystalline patterns in Rydberg experiments. An outcome that generated considerable interest in the community is the proposal of a novel architecture for adiabatic quantum computers that also lead to a patent application.