Spin pump turnstile: Parametric pumping of a spin-polarized current through a nearly closed quantum dot

We investigate parametric pumping of a spin-polarized current through a nearly closed quantum dot in a perpendicular magnetic field. Pumping is achieved by tuning the tunnel couplings to the left and right lead-thereby operating the quantum dot as a turnstile-and changing either the magnetic field or a gate voltage. We analyze the quantum dynamics of a pumping cycle and the limiting time scales for operating the quantum dot turnstile as a pure spin pump. The proposed device can be used as a fully controllable double-sided and bipolar spin filter and to inject spins on demand.