Frustration and Kinetic Magnetism in a Cold-Atom Quantum Simulator*

We present recent experimental advances in the quantum simulation of strongly correlated materials with ultracold fermions, revealing emergent magnetic states in a Hubbard model with tunable geometric frustration and doping. Using an optical lattice that transitions from a square to a triangular geometry, we observe the transformation of a Néel antiferromagnet into a short-range 120° spiral state at half-filling due to frustration. Beyond half-filling, antiferromagnetic correlations strengthen with hole dopants but intriguingly reverse to ferromagnetic with particle dopants. By measuring three-point dopant-spin-spin correlations, we uncover the emergence of ferromagnetic polarons, offering the first cold-atom observation of Nagaoka ferromagnetism. Our work provides insights into kinetic magnetism, akin to observations in twisted TMD bilayers, and opens new avenues for exploring dopant pairing mediated by frustration.