Multimode quantum correlations of soliton microcombs in silicon carbide photonics

Soliton microcombs may possess multimode entanglement across their spectral modes. In this work, we measure second-order photon correlations between the below-threshold modes of a soliton crystal in an integrated silicon carbide microresonator and match the correlation matrix to the theoretical model based on the linearization of soliton optical fields; we infer the entanglement structure of the state. In addition, we study the underlying quantum processes of three stages of soliton formation: (i) the below-threshold biphoton comb, (ii) the merging of secondary combs, and (iii) merged but not-yet phase-locked secondary combs.