  Quantum-mechanical correlations of interacting fermions result in the
emergence of exotic phases. Magnetic phases naturally arise in the
Mott-insulator regime of the Fermi-Hubbard model, where charges are localized
and the spin degree of freedom remains. In this regime, the occurrence of
phenomena such as resonating valence bonds, frustrated magnetism, and spin
liquids is predicted. Quantum systems with engineered Hamiltonians can be used
as simulators of such spin physics to provide insights beyond the capabilities
of analytical methods and classical computers. To be useful, methods for the
preparation of intricate many-body spin states and access to relevant
observables are required. Here, we show the quantum simulation of magnetism in
the Mott-insulator regime with a linear quantum-dot array. We characterize the
energy spectrum for a Heisenberg spin chain, from which we can identify when
the conditions for homogeneous exchange couplings are met. Next, we study the
multispin coherence with global exchange oscillations in both the singlet and
triplet subspace of the Heisenberg Hamiltonian. Last, we adiabatically prepare
the low-energy global singlet of the homogeneous spin chain and probe it with
two-spin singlettriplet measurements on each nearest-neighbor pair and the
correlations therein. The methods and control presented here open new
opportunities for the simulation of quantum magnetism benefiting from the
flexibility in tuning and layout of gate-defined quantum-dot arrays.
