  A generic kind of quantum chaotic ratchet is introduced, based on initial
states that are \emph{uniform} in phase space with the \emph{maximal possible}
resolution of one Planck cell. Unlike a classical phase-space uniform density,
such a state usually carries a \emph{nonzero} ratchet current, even in
\emph{symmetric} systems. This quantum ratchet effect basically emerges from
the generic asymmetry of the state quasicoordinates in the Planck cell. It is
shown, on the basis of exact results, general arguments, and extensive
numerical evidence, that in a semiclassical full-chaos regime the variance of
the current over all the states is nearly proportional to the chaotic-diffusion
rate and to the square of the scaled Planck constant. Experimental realizations
are suggested.
