Current noise spectrum of a quantum shuttle

TL;DR

This paper introduces a method to calculate the full current noise spectrum in nano-electromechanical systems, specifically applied to a quantum shuttle, revealing peaks at multiples of the mechanical frequency and explaining current deviations.

Contribution

The paper develops a novel approach for computing the current noise spectrum in NEMS and applies it to a quantum shuttle, uncovering detailed spectral features and mechanisms of charge transport.

Findings

Noise spectrum peaks at integer multiples of mechanical frequency

Renormalization of mechanical frequency explains current deviations

Coexistence regime involves two charge transport mechanisms

Abstract

We present a method for calculating the full current noise spectrum for the class of nano-electromechanical systems (NEMS) that can be described by a Markovian generalized master equation. As a specific example we apply the method to a quantum shuttle. The noise spectrum of the shuttle has peaks at integer multiples of the mechanical frequency, which is slightly renormalized. The renormalization explains a previously observed small deviation of the shuttle current compared to the expected value given by the product of the natural mechanical frequency and the electron charge. For a certain parameter range the quantum shuttle exhibits a coexistence regime, where the charges are transported by two different mechanisms: shuttling and sequential tunneling. In our previous studies we showed that characteristic features in the zero-frequency noise could be quantitatively understood as a slow switching process between the two current channels, and the present study shows that this interpretation holds also qualitatively at finite frequency.