Séminaire de Physique ThéoriqueQuantum resonances, current reversals and chaos in ratchet systems
Anatole Kenfack (MPI, Dresden, Germany)
Thursday 15 November 2007 14:00 - Tours - Salle 1180 (Bât E2)
The Ratchet effect, that is the possibility of directed transport without bias (net force) in systems with broken symmetries is discussed. The Ratchet model is first briefly introduced, starting from its birth which can be traced back to a gedanken experiment performed by Smulochowski in 1912 to its thermodynamic's formulation by Feymann in 1963. The growing interest of this Ratchet effect is then demonstrated with a variety of existing applications in a large domain of science. Some examples of commonly studied Ratchets are shown both in classical and in quantum worlds. Specifically we present a recipes for conviniently calculating the current and discuss the origin of current reversals in a classically chaotic ratchet systems. Finally we consider a model of cold atoms trapped in a optical lattice ratchet potential which can be continuously switched off and on (flashing ratchet). We show that by controlling the strength of the potential, high-order quantum resonances may naturally emerge and can induce not only current reversals, but also larger current than low-order resonances. We also show that these intriguing quantum phenomena can only be observed for fully chaotic classical dynamics.