Hidden quantum pump effects in quantum coherent rings

TL;DR

This paper investigates how time-periodic perturbations in quantum rings can generate net currents, especially highlighting the transition from no net current at low frequencies to resonant net currents at higher frequencies.

Contribution

It introduces a detailed analysis of quantum pump effects in coherent rings, emphasizing the role of frequency and resonances in current generation.

Findings

Small amplitude, low-frequency perturbations produce side band currents that cancel out.

Higher pump frequencies can induce resonant excitations leading to net pumped currents.

The study uses a quantum dot in a ring to illustrate the theoretical results.

Abstract

Time periodic perturbations of an electron system on a ring are examined. For small frequencies periodic small amplitude perturbations give rise to side band currents which in leading order are inversely proportional to the frequency. These side band currents compensate the current of the central band such that to leading order no net pumped current is generated. In the non-adiabatic limit, larger pump frequencies can lead to resonant excitations: as a consequence a net pumped current arises. We illustrate our results for a one channel ring with a quantum dot whose barriers are modulated parametrically.