A single-atom 3D sub-attonewton force sensor

TL;DR

This paper introduces a highly sensitive three-dimensional force sensor using a single laser-cooled ion, achieving sub-attonewton precision by imaging ion fluorescence and measuring displacement without mechanical oscillation.

Contribution

The work demonstrates a novel 3D force sensor based on super-resolution fluorescence imaging of a single ion, reaching sensitivities close to the quantum limit and applicable to various force detection scenarios.

Findings

Achieved 372, 347, and 808 zN/√Hz sensitivities in three dimensions.

Verified measurement accuracy using light pressure force of 95 zN.

Sensor can detect DC and low-frequency forces from external or internal sources.

Abstract

All physical interactions are mediated by forces. Ultra-sensitive force measurements are therefore a crucial tool for investigating the fundamental physics of magnetic, atomic, quantum, and surface phenomena. Laser cooled trapped atomic ions are a well controlled quantum system and a standard platform for precision metrology. Their low mass, strong Coulomb interaction, and readily detectable fluorescence signal make trapped ions favourable for performing high-sensitivity force measurements. Here we demonstrate a three-dimensional sub-attonewton sensitivity force sensor based on super-resolution imaging of the fluorescence from a single laser cooled $^{174}$Yb$^+$ ion in a Paul trap. The force is detected by measuring the net ion displacement with nanometer precision, and does not rely on mechanical oscillation. Observed sensitivities were 372$\pm$9$_\mbox{stat}$, 347$\pm$12$_\mbox{sys}\pm$14$_\mbox{stat}$, and 808$\pm$29$_\mbox{sys}\pm$42$_\mbox{stat}$ zN/$\sqrt{\mbox{Hz}}$ in the three dimensions, corresponding to 24x, 87x, and 21x of the quantum limit. We independently verified the accuracy of this apparatus by measuring a light pressure force of 95 zN on the ion, an important systematic effect in any optically based force sensor. This technique can be applied for sensing DC or low frequency forces external to the trap or internally from a co-trapped biomolecule or nanoparticle.