Efficient Quantum Ratchet
  Quantum resonance is one of the main characteristics of the quantum kicked rotor, which has been used to induce accelerated ratchet current of the particles with a generalized asymmetry potential. Here we show that by desynchronizing the kicked potentials of the flashing ratchet [Phys. Rev. Lett. 94, 110603 (2005)], new quantum resonances are stimulated to conduct directed currents more efficiently. Most distinctly, the missed resonances $\kappa=1.0\pi$ and $\kappa=3.0\pi$ are created out to induce even larger currents. At the same time, with the help of semiclassical analysis, we prove that our result is exact rather than phenomenon induced by errors of the numerical simulation. Our discovery may be used to realize directed transport efficiently, and may also lead to a deeper understanding of symmetry breaking for the dynamical evolution. 
Chuan-Feng Li, Rong-Chun Ge, Guang-Can Guo
quant-ph cond-mat.other