A nanomechanical resonator coupled linearly via its momentum to a quantum point contact

TL;DR

This paper investigates a nanoelectromechanical system where a resonator is coupled via its momentum to a quantum point contact, revealing quantum correlations, noise squeezing, and non-trivial back-action effects through a master equation approach.

Contribution

It introduces a detailed master equation analysis of momentum-coupled resonator-QPC systems, highlighting quantum correlations and non-classical noise phenomena.

Findings

Quantum correlations between current and back-action force are maximized at a specific tunneling phase.

The oscillator's steady state can exhibit thermomechanical noise squeezing.

Half of the detector back-action correlates with electron tunneling, indicating non-trivial back-action effects.

Abstract

We use a Born-Markov approximated master equation approach to study the symmetrized-in-frequency current noise spectrum and the oscillator steady state of a nanoelectromechanical system where a nanoscale resonator is coupled linearly via its momentum to a quantum point contact (QPC). Our current noise spectra exhibit clear signatures of the quantum correlations between the QPC current and the back-action force on the oscillator at a value of the relative tunneling phase (\eta = -\pi/2) where such correlations are expected to be maximized. We also show that the steady state of the oscillator obeys a classical Fokker-Planck equation, but can experience thermomechanical noise squeezing in the presence of a momentum-coupled detector bath and a position-coupled environmental bath. Besides, the full master equation clearly shows that half of the detector back-action is correlated with electron tunneling, indicating a departure from the model of the detector as an effective bath and suggesting that a future calculation valid at lower bias voltage, stronger tunneling and/or stronger coupling might reveal interesting quantum effects in the oscillator dynamics.