Quantum Ratchets on Maximally Uniform States in Phase Space: Semiclassical Full-Chaos Regime

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.