  Turbulent convection plays a crucial role in many natural environments,
ranging from Earth ocean, mantle and outer core, to various astrophysical
systems. For such flows with extremely strong thermal driving, an ultimate
scaling was proposed for the heat flux and velocity. Despite numerous
experimental and numerical studies, a conclusive observation of the ultimate
regime has not been reached yet. Here we show that the ultimate scaling can be
perfectly realized once the thermal boundary layer is fully decoupled from the
viscous boundary layer and locates inside the turbulent bulk. The heat flux can
be greatly enhanced by one order of magnitude. Our results provide concrete
evidences for the appearance of the ultimate state when the entire thermal
boundary layer is embedded in the turbulent region, which is probably the case
in many natural convection systems.
