Observation of separated dynamics of charge and spin in the Fermi-Hubbard model

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.