  Dissipative Kerr soliton (DKS) microcomb has emerged as an enabling
technology that revolutionizes a wide range of applications in both basic
science and technological innovation. Reliable turnkey operation with
sub-opticalcycle and sub-femtosecond timing jitter is key to the success of
many intriguing microcomb applications at the intersection of ultrafast optics
and microwave electronics. Here we propose a novel approach to demonstrate the
first turnkey Brillouin-DKS frequency comb. Our approach with a Chimera cavity
offers essential benefits that are not attainable previously, including phase
insensitivity, self-healing capability, deterministic selection of DKS state,
and access to the ultralow noise comb state. The demonstrated turnkey
Brillouin-DKS frequency comb achieves a fundamental comb linewidth of 100 mHz
and DKS timing jitter of 1 femtosecond for averaging times up to 56 {\mu}s. The
approach is universal and generalizable to various device platforms for
user-friendly and field-deployable comb devices.
