Levitated nano-trampoline resonators for magnetic field sensing
Levitated systems and high-$Q$ membrane nanomechanical resonators have achieved exceptional sensitivity in precision sensing, but functionalizing such resonators for practical applications without degrading their low dissipation remains challenging. Here, we combine diamagnetic levitation with a high-$Q$ nanomechanical resonator to realize a high-precision magnetometer for sensing weak oscillating magnetic fields. A macroscopic diamagnetically levitated graphite plate acts as a free-floating proof mass that couples strongly to magnetic fields, converting them into mechanical motion that is resonantly amplified by a low-dissipation nano-trampoline resonator. Operating at room temperature and without magnetic shielding, we achieve a peak magnetic-field sensitivity of $4.5\, \mathrm{pT}/\sqrt{\mathrm{Hz}}$ using a resonator with a mechanical quality factor of $Q=6\times10^{6}$ at $443\, \mathrm{kHz}$. The system sensitivity is limited by thermomechanical noise. With further improvements in mechanical $Q$, this hybrid levitated platform offers a pathway toward femtotesla-level AC magnetic-field sensing, establishing diamagnetically levitated nanomechanical resonators as a new class of high-sensitivity magnetometers at room temperature.