  Understanding how interacting particles approach thermal equilibrium is a
major challenge of quantum simulators. Unlocking the full potential of such
systems toward this goal requires flexible initial state preparation, precise
time evolution, and extensive probes for final state characterization. We
present a quantum simulator comprising 69 superconducting qubits which supports
both universal quantum gates and high-fidelity analog evolution, with
performance beyond the reach of classical simulation in cross-entropy
benchmarking experiments. Emulating a two-dimensional (2D) XY quantum magnet,
we leverage a wide range of measurement techniques to study quantum states
after ramps from an antiferromagnetic initial state. We observe signatures of
the classical Kosterlitz-Thouless phase transition, as well as strong
deviations from Kibble-Zurek scaling predictions attributed to the interplay
between quantum and classical coarsening of the correlated domains. This
interpretation is corroborated by injecting variable energy density into the
initial state, which enables studying the effects of the eigenstate
thermalization hypothesis (ETH) in targeted parts of the eigenspectrum.
Finally, we digitally prepare the system in pairwise-entangled dimer states and
image the transport of energy and vorticity during thermalization. These
results establish the efficacy of superconducting analog-digital quantum
processors for preparing states across many-body spectra and unveiling their
thermalization dynamics.
