  The repulsive Hubbard Hamiltonian is one of the foundational models
describing strongly correlated electrons and is believed to capture essential
aspects of high temperature superconductivity. Ultracold fermions in optical
lattices allow for the simulation of the Hubbard Hamiltonian with a unique
control over kinetic energy, interactions and doping. A great challenge is to
reach the required low entropy and to observe antiferromagnetic spin
correlations beyond nearest neighbors, for which quantum gas microscopes are
ideal. Here we report on the direct, single-site resolved detection of
antiferromagnetic correlations extending up to three sites in spin-$1/2$
Hubbard chains, which requires an entropy well below $s^*=\ln(2)$. Finally, the
simultaneous detection of spin and density opens the route towards the study of
the interplay between magnetic ordering and doping in various dimensions.
