Noise spectrum of a tunnel junction coupled to a nanomechanical oscillator

TL;DR

This paper investigates how a nanomechanical oscillator coupled to a tunnel junction affects the current noise spectrum, revealing peaks at specific frequencies and proposing a method to measure the oscillator's occupation number using noise analysis.

Contribution

It provides a comprehensive analysis of the noise spectrum for arbitrary conditions and introduces a novel way to determine the oscillator's occupation number via noise peaks.

Findings

Noise spectrum has peaks at zero, oscillator, and twice the oscillator frequency.

The influence of the oscillator disappears below the bias voltage threshold.

The oscillator occupation number can be inferred from the noise peak at the oscillator frequency.

Abstract

A nanomechanical resonator coupled to a tunnel junction is studied. The oscillator modulates the transmission of the junction, changing the current and the noise spectrum. The influence of the oscillator on the noise spectrum of the junction is investigated, and the noise spectrum is obtained for arbitrary frequencies, temperatures and bias voltages. We find that the noise spectrum consists of a noise floor and a peaked structure with peaks at zero frequency, the oscillator frequency and twice the oscillator frequency. The influence of the oscillator vanishes if the bias voltage of the junction is lower than the oscillator frequency. We demonstrate that the peak at the oscillator frequency can be used to determine the oscillator occupation number, showing that the current noise in the junction functions as a thermometer for the oscillator.