  Strongly correlated quantum systems give rise to many exotic physical
phenomena, including high-temperature superconductivity. Simulating these
systems on quantum computers may avoid the prohibitively high computational
cost incurred in classical approaches. However, systematic errors and
decoherence effects presented in current quantum devices make it difficult to
achieve this. Here, we simulate the dynamics of the one-dimensional
Fermi-Hubbard model using 16 qubits on a digital superconducting quantum
processor. We observe separations in the spreading velocities of charge and
spin densities in the highly excited regime, a regime that is beyond the
conventional quasiparticle picture. To minimize systematic errors, we introduce
an accurate gate calibration procedure that is fast enough to capture temporal
drifts of the gate parameters. We also employ a sequence of error-mitigation
techniques to reduce decoherence effects and residual systematic errors. These
procedures allow us to simulate the time evolution of the model faithfully
despite having over 600 two-qubit gates in our circuits. Our experiment charts
a path to practical quantum simulation of strongly correlated phenomena using
available quantum devices.
