Adiabatic almost-topological pumping of fractional charges in noninteracting quantum dots

Abstract

We use exact techniques to demonstrate theoretically the pumping of fractional charges in a single-level non-interacting quantum dot, when the dot-reservoir coupling is adiabatically driven from weak to strong coupling. The pumped charge averaged over many cycles is quantized at a fraction of an electron per cycle, determined by the ratio of Lamb shift to level-broadening; this ratio is imposed by the reservoir band-structure. For uniform density of states, half an electron is pumped per cycle. We call this adiabatic almost-topological pumping, because the pumping's Berry curvature is sharply peaked in the parameter space. Hence, so long as the pumping contour does not touch the peak, the pumped charge depends only on how many times the contour winds around the peak (up to exponentially small corrections). However, the topology does not protect against non-adiabatic corrections, which grow linearly with pump speed. In one limit the peak becomes a delta-function, so the adiabatic pumping of fractional charges becomes entirely topological. Our results show that quantization of the adiabatic pumped charge at a fraction of an electron does not require fractional particles or other exotic physics.

Topological charge and spin pumping in a semiconductor nanowire

“…Both experimentally and theoretically, the adiabatic quantum pumping of electron charge and spin in semiconductor nanostructures are always one of the hotspot issue due to the state-of-the-art nanotechnology [15][16][17][18][19][20][21][22][23][24] . Especially, the parametric pumping facilitates the adiabatic quantum transfer of noninteracting electrons in unbiased quantum dots [16][17][18] , but the transferred number in a cycle is not necessarily quantized under this pump scheme 16,17 .…”