Directed Transport of Atoms in a Hamiltonian Quantum Ratchet

Abstract

Moving Cold Atoms with Quantum Ratchets The nanoscale dimensions of biological motors make them susceptible to thermal noise, but such motors can produce force in one direction by alternating application of an asymmetric potential, or ratchet, with periods of thermal drift in the motion. The quantum version of such motors can operate without dissipation, as long as there is some means to break time-reversal symmetry in the system. Salger et al. (p. 1241 ) report on a coherent quantum ratchet device consisting of Bose-Einstein condensate cold atoms placed into an asymmetric sawtooth-potential created by optical lattices. Symmetry breaking was accomplished by phase shifts in the driving potentials. As expected for such a quantum ratchet, the current depended on the initial phase of the driving potential.