Experimental realization of the symmetry-protected Haldane phase in Fermi-Hubbard ladders

The Haldane antiferromagnetic spin-1 chain constitutes a paradigmatic model of a quantum system which holds a symmetry protected topological phase. Here, we experimentally realize the Haldane phase using Fermi-Hubbard ladders in an ultracold quantum gas microscope. Site-resolved potential shaping allows us to create tailored spin-1/2 geometries which permit the exploration of such a topological chain and its comparison to a trivial configuration. We use spin- and density-resolved measurements to probe edge and bulk properties of the system, revealing a clear dinstinction between the trivial and topological cases. The measurement of a non-local string order parameter, in particular, allows to directly capture the underlying protecting symmetry of the topological phase. We furthermore investigate the robustness of the topological phase upon the onset of density fluctuations by tuning the Hubbard interaction.