Session H02: Frontiers of Quantum Simulations -- Revealing Hidden Symmetries and Novel Excitations

When the complex nature of atoms can really make a difference: ultracold erbium and dysprosium for quantum simulation

Since its creation, the field of ultracold atoms has been through fantastic developments. Some of the most recent include the development of quantum-gas microscopes, atom tweezers, and various forms of interaction engineering. Each of these experimental advances has allowed new quantum phenomena to be accessed and observed. A further important development is based on the use of more exotic atomic species, whose peculiar atomic properties have allowed to broaden the horizons of investigation.

This talk aims to retrace the new opportunities that have emerged from the use of quantum gases composed of the strongly magnetic erbium and dysprosium atoms from the perspective of the Innsbruck experiments.

Thanks to their large magnetic moment, these species exhibit a large dipolar interaction that has allowed us to observe rotonic excitations, quantum droplets, and supersolid states. Moreover, their dense atomic spectrum has also made possible to implement new optical manipulation schemes, and more recently the observation of an Hz-wide transition in the telecom frequency region promises new possibilities in quantum optics.   

Quantum simulation of Fermi-Hubbard dynamics and bosonic Laughlin states

Quantum simulations with ultracold atoms in optical lattices expand into new regimes with ample room for discovery. I will present work that investigates the intricate interplay between spin and charge in the Fermi-Hubbard model, and that gives evidence for magnetic polarons, whose dynamics may explain emergent properties of quantum materials such as high-temperature superconductivity. We directly observe the formation dynamics and subsequent spreading of individual magnetic polarons, enabling the study of out-of-equilibrium emergent phenomena in the Fermi-Hubbard model, one dopant at a time. In our bosonic work we realize strongly correlated topological states of matter and find evidence for a two-particle fractional quantum Hall state following a bottom-up approach.    

Strongly correlated matter with ultracold atoms: From the Hubbard model to Z2 lattice gauge theory

Ultracold atoms in optical potentials have made great progress over the past few years, and provide the most promising platform for quantum simulations of strongly correlated quantum matter. Indeed, these platforms have already begun to study some of the most challenging open problems in theoretical physics, including the search for the origin of high-temperature superconductivity in the Fermi-Hubbard model and the realization of quantum spin liquids hosting non-trivial topological excitations. I will start this talk by giving a brief overview how far the quantum simulation of the doped Fermi-Hubbard model has already come. Then I will explain how such doped quantum magnets can, in some instances, be directly mapped to Z₂ lattice gauge theories with dynamical matter. On the one hand this allows for an elegant description of hidden string order in these systems and lends a natural explanation to stripe phases. On the other hand, it motivates the search for meson-type excitations - a hallmark feature of lattice gauge theories - in a larger class of doped quantum magnets. I will present recent numerical results pointing to a rich emergent structure of charge carriers in strongly correlated quantum materials, and discuss how these theoretical predictions can result in direct experimental verifications using ultracold atoms. I will close the talk with an outlook how a paradigmatic Z₂ lattice gauge theory with dynamical matter can be realized with current technology in 2D Rydberg arrays.   

Observing the emergence of many body physics, atom by atom

We prepare samples of up to 20 fermionic atoms with ultralow entropies in a two-dimensional configuration. We developed a single atom and spin sensitive imaging technique that allows us to detect all atoms of a samlpe either in real, or in momentum space. From such measurements we can infer correlations in the system. In our fermonic system, these are present already in a noninteracting sample and give rise to so-called Pauli Crystals [1]. More interesting correlations arise as soon as interactions in the system are turned on. Now, Cooper pairs and a BCS-like system can be observed to form with p,-p - correlations emerging at the Fermi surface [3]. In our trapped finite system, pairing occurs only at a finite attraction strength, which results in the precursor of a quantum phase transition [2]. To further understand the emergence of many body physics from the few-body limit we are currently exploring a single impurity in a finite Fermi sea to observe the transition from a molecular to a polaronic state. We will present progress on our quest to understand the polaron from the correlations between its constituents.