  Quantum simulators are engineered devices controllably designed to emulate
complex and classically intractable quantum systems. A key challenge is to
certify whether the simulator truly mimics the Hamiltonian of interest. This
certification step requires the comparison of a simulator's output to a known
answer, which is usually limited to small systems due to the exponential
scaling of the Hilbert space. Here, in the context of Fermi-Hubbard spin-based
analogue simulators, we propose a modular many-body spin to charge conversion
scheme that scales linearly with both the system size and the number of
low-energy eigenstates to discriminate. Our protocol is based on the global
charge state measurement of a 1D spin chain performed at different detuning
potentials along the chain. In the context of semiconductor-based systems, we
identify realistic conditions for detuning the chain adiabatically in order to
avoid state mixing while preserving charge coherence. Large simulators with
vanishing energy gaps, including 2D arrays, can be certified block-by-block
with a number of measurements scaling only linearly with the system size.
