Truncated nonlinear interferometry for quantum enhanced atomic force microscopy

TL;DR

This paper demonstrates a practical quantum-enhanced atomic force microscopy technique using nonlinear interferometry, achieving noise reduction and high-precision displacement measurements with potential for broadband, high-speed scanning.

Contribution

It presents the first practical implementation of nonlinear interferometry in atomic force microscopy, achieving quantum noise reduction and improved measurement precision.

Findings

Quantum noise reduction of up to 3 dB below SQL

Displacement measurement precision of 1.7 fm/√Hz

Minimized photon backaction noise using squeezed states

Abstract

Nonlinear interferometers that replace beamsplitters in Mach-Zehnder interferometers with nonlinear amplifiers for quantum-enhanced phase measurements have drawn increasing interest in recent years, but practical quantum sensors based on nonlinear interferometry remain an outstanding challenge. Here, we demonstrate the first practical application of nonlinear interferometry by measuring the displacement of an atomic force microscope microcantilever with quantum noise reduction of up to 3~dB below the standard quantum limit, corresponding to a quantum-enhanced measurement of beam displacement of $\mathrm{1.7~fm/\sqrt{Hz}}$. Further, we show how to minimize photon backaction noise while taking advantage of quantum noise reduction by transducing the cantilever displacement signal with a weak squeezed state while using dual homodyne detection with a higher power local oscillator. This approach offers a path toward quantum-enhanced broadband, high-speed scanning probe microscopy.