Optical levitation of 10 nanogram spheres with nano-$g$ acceleration sensitivity

TL;DR

This paper demonstrates optical levitation of nanogram silica spheres with unprecedented acceleration sensitivity, enabling precise measurements and revealing absorption-related mass loss at high vacuum.

Contribution

It introduces techniques for levitating larger nanogram spheres with high sensitivity and characterizes absorption effects limiting sphere size in optical levitation.

Findings

Achieved acceleration sensitivity of 0.4×10^{-6} g/√Hz for 12 ng spheres

Measured mean acceleration of approximately -0.7×10^{-9} g over 1.4×10^4 seconds

Identified absorption-induced mass loss in high vacuum for spheres larger than 10 ng

Abstract

We demonstrate optical levitation of SiO$_2$ spheres with masses ranging from 0.1 to 30 nanograms. In high vacuum, we observe that the measured acceleration sensitivity improves for larger masses and obtain a sensitivity of $0.4 \times 10^{-6}\ g/\sqrt{\mathrm{Hz}}$ for a 12 ng sphere, more than an order of magnitude better than previously reported for optically levitated masses. In addition, these techniques permit long integration times and a mean acceleration of $(-0.7\pm2.4\,[stat] \pm 0.2\,[syst])\times ~ 10^{-9}\,g$ is measured in $1.4\times 10^4$~s. Spheres larger than 10~ng are found to lose mass in high vacuum where heating due to absorption of the trapping laser dominates radiative cooling. This absorption constrains the maximum size of spheres that can be levitated and allows a measurement of the absorption of the trapping light for the commercially available spheres tested here. Spheres consisting of material with lower absorption may allow larger objects to be optically levitated in high vacuum.