Position measurement of a levitated nanoparticle via interference with its mirror image

TL;DR

This paper introduces a self-interference technique using a mirror to detect the motion of a levitated nanoparticle, overcoming mode mismatch issues in interferometry, and demonstrates improved feedback cooling performance.

Contribution

The authors develop and experimentally validate a mirror-based self-interference method for nanoparticle position measurement, enhancing detection efficiency and cooling capabilities.

Findings

Achieved a detection sensitivity of 1.7×10⁻¹² m/√Hz.

Demonstrated feedback cooling to temperatures below previous methods.

Implemented a high-vacuum Paul trap with mirror retro-reflection for nanoparticle motion detection.

Abstract

Interferometric methods for detecting the motion of a levitated nanoparticle provide a route to the quantum ground state, but such methods are currently limited by mode mismatch between the reference beam and the dipolar field scattered by the particle. Here we demonstrate a self-interference method to detect the particle's motion that solves this problem. A Paul trap confines a charged dielectric nanoparticle in high vacuum, and a mirror retro-reflects the scattered light. We measure the particle's motion with a sensitivity of $1.7\times 10^{-12} \text{m}/\sqrt{\text{Hz}}$, corresponding to a detection efficiency of 2.1%, with a numerical aperture of 0.18. As an application of this method, we cool the particle, via feedback, to temperatures below those achieved in the same setup using a standard position measurement.