Intrinsic noise properties of atomic point contact displacement detectors

TL;DR

This paper characterizes the noise properties of atomic point contact displacement detectors, demonstrating high measurement speed and sensitivity close to quantum limits at cryogenic temperatures.

Contribution

It introduces a microwave technique that significantly enhances the measurement speed of atomic point contacts for displacement detection.

Findings

Achieved shot-noise limited imprecision of 2.3 fm/√Hz

Detected nanomechanical resonances up to 60 MHz

Observed backaction force of 78 aN/√Hz

Abstract

We measure the noise added by an atomic point contact operated as a displacement detector. With a microwave technique, we increase the measurement speed of atomic point contacts by a factor of 500. The measurement is then fast enough to detect the resonant motion of a nanomechanical beam at frequencies up to 60 MHz and sensitive enough to observe the random thermal motion of the beam at 250 mK. We demonstrate a shot-noise limited imprecision of $2.3\pm0.1\ \mathrm{fm/\sqrt{Hz}}$ and observe a $78\pm20 \mathrm{aN/\sqrt{Hz}}$ backaction force, yielding a total uncertainty in the beam's displacement that is $42\pm9$ times the standard quantum limit.