  Soliton microcombs -- phase-locked microcavity frequency combs -- have become
the foundation of several classical technologies in integrated photonics,
including spectroscopy, LiDAR, and optical computing. Despite the predicted
multimode entanglement across the comb, experimental study of the quantum
optics of the soliton microcomb has been elusive. In this work, we use
second-order photon correlations to study the underlying quantum processes of
soliton microcombs in an integrated silicon carbide microresonator. We show
that a stable temporal lattice of solitons can isolate a multimode
below-threshold Gaussian state from any admixture of coherent light, and
predict that all-to-all entanglement can be realized for the state. Our work
opens a pathway toward a soliton-based multimode quantum resource.
