Back-action Evading Measurements of Nanomechanical Motion

TL;DR

This paper demonstrates a back-action evading measurement technique on a nanomechanical resonator, achieving sensitivities beyond the standard quantum limit and cooling close to the quantum ground state.

Contribution

The authors experimentally realize a device that performs back-action evading measurements, surpassing quantum sensitivity limits and demonstrating quantum state control of a nanomechanical resonator.

Findings

Back-action evading detection with 4 times quantum zero-point sensitivity

Cooling of mechanical resonator to 12 quanta

Position resolution 1.3 times quantum zero-point motion

Abstract

When performing continuous measurements of position with sensitivity approaching quantum mechanical limits, one must confront the fundamental effects of detector back-action. Back-action forces are responsible for the ultimate limit on continuous position detection, can also be harnessed to cool the observed structure, and are expected to generate quantum entanglement. Back-action can also be evaded, allowing measurements with sensitivities that exceed the standard quantum limit, and potentially allowing for the generation of quantum squeezed states. We realize a device based on the parametric coupling between an ultra-low dissipation nanomechanical resonator and a microwave resonator. Here we demonstrate back-action evading (BAE) detection of a single quadrature of motion with sensitivity 4 times the quantum zero-point motion, back-action cooling of the mechanical resonator to n = 12 quanta, and a parametric mechanical pre-amplification effect which is harnessed to achieve position resolution a factor 1.3 times quantum zero-point motion.