A background-free optically levitated charge sensor

TL;DR

This paper presents a novel background-free optically levitated charge sensor that models and eliminates dipole interactions, achieving unprecedented sensitivity and enabling detection of extremely small charges.

Contribution

It introduces a new technique to eliminate dipole effects in levitated sensors, significantly improving charge detection sensitivity.

Findings

Achieved a sensitivity of 3.3×10⁻⁵e in charge measurement.

Demonstrated detection of charges much smaller than an electron.

Enabled measurement of electromagnetic properties of levitated objects.

Abstract

Optically levitated macroscopic objects are a powerful tool in the field of force sensing, owing to high sensitivity, absolute force calibration, environmental isolation and the advanced degree of control over their dynamics that have been achieved. However, limitations arise from the spurious forces caused by electrical polarization effects that, even for nominally neutral objects, affect the force sensing because of the interaction of dipole moments with gradients of external electric fields. In this paper we introduce a new technique to model and eliminate dipole moment interactions limiting the performance of sensors employing levitated objects. This process leads to the first noise-limited measurement with a sensitivity of $3.3\times10^{-5}e$. As a demonstration, this is applied to the search for unknown charges of a magnitude much below that of an electron or for exceedingly small unbalances between electron and proton charges. The absence of remaining systematic biases, enables true discovery experiments, with sensitivities that are expected to improve as the system noise is brought down to or beyond the quantum limit. As a by-product of the technique, the electromagnetic properties of the levitated objects can also be measured on an individual basis.