  We demonstrate the first compact photonic flywheel with sub-fs time jitter
(averaging times up to 10 {\mu}s) at the quantum-noise limit of a monolithic
fiber resonator. Such quantum-limited performance is accessed through novel
two-step pumping scheme for dissipative Kerr soliton (DKS) generation.
Controllable interaction between stimulated Brillouin lasing and Kerr
nonlinearity enhances the DKS coherence and mitigate the thermal instability
challenge, achieving a remarkable 22-Hz intrinsic comb linewidth and an
unprecedented phase noise of -180 dBc/Hz at 945 MHz carrier at free running.
The scheme can be generalized to various device platforms for field-deployable
precision metrology.
