Quantum pump in quantum spin Hall edge states

• Applying two ac gate voltages can break the time-reversal symmetry and induce pumping currents.
• The pump currents display different pump frequency dependence for weak and strong e–e interaction.
• These unique properties can be used to detect and control edge states.

We present a theory for quantum pump in a quantum spin Hall bar with two quantum point contacts (QPCs). The pump currents can be generated by applying harmonically modulating gate voltages at QPCs. The phase difference between the gate voltages introduces an effective gauge field, which breaks the time-reversal symmetry and generates pump currents. The pump currents display very different pump frequency dependence for weak and strong e–e interaction. These unique properties are induced by the helical feature of the edge states, and therefore can be used to detect and control edge state transport.