An Autonomous Topological Pump

Abstract

Robust quantization of particle transport, as in a Thouless pump, is a hallmark of topological quantum systems with externally controlled system parameters. Here we instead propose and analyze a Thouless pump, for fermions in a one-dimensional lattice, in which external control is not needed, because an additional dynamical degree of freedom allows the pump to work autonomously. The external control parameters are replaced by a quantum spin in a static magnetic field, so that Larmor precession of the spin performs the control cycle that induces topologically quantized transport of the fermions -- at least in some higher energy eigenstates of the combined system. In other states, the back-action of the fermions on the spin can distort the control cycle enough to disrupt the transport, but we find numerical evidence for a critical value of the magnetic field above which the autonomous pump works with topological robustness, suggesting that topological protection and autonomous operation together may permit robust "quantum motors".