Dynamics of a Ferromagnetic Particle Levitated over a Superconductor

According to recent predictions, a microscale ferromagnetic needle will precess under the influence of a small applied torque, if sufficiently isolated from the environment. In fact, such a system could be used to measure torques with a sensitivity far surpassing the standard quantum limit for a free ensemble of spins. To observe precession and carry out ultrasensitive torque measurements, the ferromagnetic needle requires nearly frictionless suspension. Here crucial initial steps are realized by levitating a micrometer-scale ferromagnetic particle above superconducting Nb and investigating its dynamics, including the role of trapped flux.