  In a traveling wave microresonator, the cascaded four-wave mixing between
optical modes allows the generation of frequency combs, including the
intriguing dissipative Kerr solitons (DKS). Here, we theoretically investigate
the quantum fluctuations of the comb and reveal the quantum feature of the
soliton. It is demonstrated that the fluctuations of Kerr frequency comb lines
are correlated, leading to multi-color continuous-variable entanglement. In
particular, in the DKS state, the coherent comb lines stimulate photon-pair
generation and also coherent photon conversion between all optical modes, and
exhibit all-to-all connection of quantum entanglement. The broadband
multi-color entanglement is not only universal, but also is robust against
practical imperfections, such as extra optical loss or extraordinary frequency
shift of a few modes. Our work reveals the prominent quantum nature of DKSs,
which is of fundamental interest in quantum optics and also holds potential for
quantum network and distributed quantum sensing applications.
