Surpassing the Energy Resolution Limit with ferromagnetic torque sensors

TL;DR

This paper demonstrates that ferromagnetic torque sensors can surpass the fundamental energy resolution limit and standard quantum limit, achieving unprecedented magnetic field resolution and opening new possibilities for fundamental physics research.

Contribution

It shows that energy resolution limits and quantum limits in magnetometry can be exceeded using ferromagnetic torque sensors, a novel approach in the field.

Findings

ERL can be surpassed by many orders of magnitude.

Magnetic field resolution per volume can be greatly improved.

Potential applications in searching for exotic physics interactions.

Abstract

We discuss the fundamental noise limitations of a ferromagnetic torque sensor based on a levitated magnet in the tipping regime. We evaluate the optimal magnetic field resolution taking into account the thermomechanical noise and the mechanical detection noise at the standard quantum limit (SQL). We find that the Energy Resolution Limit (ERL), pointed out in recent literature as a relevant benchmark for most classes of magnetometers, can be surpassed by many orders of magnitude. Moreover, similarly to the case of a ferromagnetic gyroscope, it is also possible to surpass the standard quantum limit for magnetometry with independent spins, arising from spin-projection noise. Our finding indicates that magnetomechanical systems optimized for magnetometry can achieve a magnetic field resolution per unit volume several orders of magnitude better than any conventional magnetometer. We discuss possible implications, focusing on fundamental physics problems such as the search for exotic interactions beyond the standard model.