In this study, we present our progress in developing a novel quantum simulator based on neutral ytterbium atoms. By combining itinerant fermionic dynamics in optical lattices with local, state-dependent control via optical tweezers, our aim is to realize a robust, scalable and programmable architecture. The ground- and metastable-state manifold of ytterbium makes it an attractive platform, and its fermionic isotopes provide nuclear-spin degrees of freedom. State-selective control of local Hamiltonian terms is enabled through magic and tune-out wavelengths, offering strong potential for various quantum simulations.
A key recent achievement was the precise determination of the excited-state tune-out wavelength for ytterbium atoms, which was previously hindered by severe losses resulting from inelastic collisions and Raman-induced photon scattering. This was made possible by isolating the atoms in an optical lattice at a magic wavelength, combined with resolved-sideband cooling on the ultra-narrow clock transition. This allows measurements to be taken at shallow lattice depths. The resulting reduction in loss rates significantly enhances the lifetime of the excited clock state. Precision measurements are further enabled by fluorescence imaging in a triple-magic configuration, where molasses cooling on the 3P1 transition is realized using a newly identified magic angle, which is reported here.
In a key step towards the quantum simulation, we realize a high-NA microscopy of fermionic ¹⁷¹Yb in a clock-magic-wavelength lattice. This provides the single-site resolution required to observe the targeted dynamics. Since the atoms are initially loaded into a three-dimensional lattice, a single two-dimensional layer must be isolated for imaging. To this end, we have developed a matter-wave refocusing scheme. Atoms that are initially occupying multiple layers of the vertical lattice are released into a tightly focused light sheet. After evolving for a quarter of a period, the atoms refocus at the center of the harmonic confinement provided by the light sheet. This allows them to be recaptured efficiently into a single lattice layer. We discuss the relevant experimental steps, including clock-state sideband cooling and fluorescence imaging with simultaneous Raman sideband cooling. Together, these results establish the imaging and control toolbox needed to perform hybrid tweezer–lattice experiments with fermionic ¹⁷¹Yb at the single-atom, single-site level. This paves the
Living systems tune their mechanics across scales by coupling biochemistry to physical mechanisms that reconfigure and strengthen in response to their surroundings. We build controlled model systems from DNA nanostars, whose liquid-liquid phase separation (LLPS) harnesses nucleic acids' design power. First, dense packings of multiphase DNA droplets form a simple prototissue: same-species droplets coalesce, while different species repel like hard spheres. These packings undergo a solid-to-liquid unjamming transition, and simulations show its sharpness depends strongly on biomolecular diversity and stoichiometry. Second, DNA droplets occupying less than 10% of an entangled actin network stiffen it 25-fold, reversibly, far beyond the roughly 25% classical theory predicts. Actin penetrates the droplets, so network elasticity in turn sets droplet size, giving reciprocal control between matrix and inclusions. We attribute the stiffening to actin entrainment, which enlarges the effective inclusions until their contact network dominates the mechanics. Together, these results show that LLPS can control not only local composition but also mechanics, pointing toward design principles for adaptive materials.
We have recently developed1 a new functional renormalization group approach (called
X-FRG) for electronic lattice models in the regime where extremely strong correlations
truncate the relevant Hilbert space. In my talk I will outline the main features of the
X-FRG and present results for the Hubbard model on a square lattice at infinite on-site
repulsion. We find that the zero-temperature phase diagram of this model exhibits Na-
gaoka ferromagnetism at high densities, a stripe antiferromagnetic phase at intermediate
densities, and a paramagnetic phase at low densities. We have also calculated the elec-
tronic spectral function which exhibits non-Fermi liquid features such as the violation of
Luttinger’s theorem and bad metal behavior.
1Jonas Arnold, Peter Kopietz, and Andreas R¨uckriegel, Phys. Rev. Lett. 137, 096506
(2026) and Phys. Rev. B 114, 055123 (2026).
It is often assumed that the single-particle spectral function of Tomonaga-Luttinger liquids — the quantity measured in photoemission and tunneling spectroscopy — has been fully understood since the early 1990s. In this talk, I will show that this belief is too optimistic. In fact, Tomonaga-Luttinger liquids, i.e. essentially one-dimensional, interacting, gapless many-fermion systems, exhibit a significantly less universal behavior than is usually claimed in the literature and textbooks. This has important implications both for the interpretation of experiments and for any theory that aims to go beyond Tomonaga-Luttinger-liquid universality.
n this talk, we review a few of Kurt Schönhammer's works from the later parts of his career. Among other things, we will talk about Luttinger liquid physics, the single impurity Anderson model, and the functional renormalization group.
I will give some highlights of our work on strongly correlated model
systems using matrix-product-state-based numerical methods, density
matrix renormalization group methods in particular. The topics will
range from an exact treatment of density functional theory on a
lattice through metal-insulator and insulator-insulator transitions,
to calculations of nonequilibrium properties such as time-dependent
spectral functions.
We investigate a strongly interacting mixture of ultracold erbium and lithium, combining sympathetic cooling with magnetic-field control of the interspecies interactions. Starting from a dual-species atomic mixture, we prepare ultracold lithium and erbium and employ sympathetic cooling to reach a deeply degenerate Fermi gas of $^6$Li, providing a versatile platform for studying interacting quantum gases.
We characterize the interspecies interactions by exploring the rich Feshbach spectrum of erbium in its absolute ground state with lithium in its three lowest hyperfine states, providing access to a strongly interacting regime. Using radio-frequency spectroscopy, we probe a superfluid spin mixture of $^6$Li in the BCS regime. We further investigate how the presence of erbium influences the RF response of the lithium superfluid.
