Surpassing the Energy Resolution Limit with Ferromagnetic Torque Sensors

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