Microscopic theory of a precessing ferromagnet for ultrasensitive magnetometry
Abstract
Levitated systems have great potential in quantum sensing and exploring quantum effects at the macroscopic scale. Of particular interest are recent works suggesting that a levitated ferromagnet can beat the standard quantum limit of magnetometry. This work offers a theoretical model to analyze and understand critical features of the precessing dynamics of a levitated ferromagnetic needle, indeed much like a macrospin, in the presence of a weak magnetic field. The dynamics from the atomic scale reveals how the standard quantum limit is surpassed, thus verifying sensing advantages when compared with a collection of independent spins. Our theory further takes us to two additional experimental designs of immediate interest: measurement of the celebrated Berry phase with a precessing ferromagnetic needle and the use of its nutation motion to sense a low-frequency oscillating magnetic field. With a microscopic theory established for levitated ferromagnetic needles, future studies of macroscopic quantum effects and the associated quantum-classical transition also become possible.
Cite
@article{arxiv.2503.00728,
title = {Microscopic theory of a precessing ferromagnet for ultrasensitive magnetometry},
author = {Xueqi Ni and Zhixing Zou and Ruvi Lecamwasam and Andrea Vinante and Dmitry Budker and Ping Koy Lam and Tao Wang and Jiangbin Gong},
journal= {arXiv preprint arXiv:2503.00728},
year = {2026}
}