BERKELEY AMO/QI SEMINAR: Changhao Xu, University of Mainz

Abstract: Levitated magnets offer a powerful route toward precision measurements by combining large magnetic moments with strongly reduced mechanical dissipation and environmental coupling. This talk presents recent experimental progress and future prospects for levitated ferromagnetic sensors. A room-temperature levitated magnet magnetometer based on diamagnetic stabilization and optical motion readout is first introduced. The device achieves a magnetic-field sensitivity of 32 fT/√Hz under ambient conditions, demonstrating that levitated magnets can reach sensitivities comparable to leading technologies such as SQUIDs and atomic magnetometers, while avoiding the need for cryogenic cooling or comparably complex magnetic shielding.

A second focus is the realization of near-free ferromagnetic dynamics. At near-zero magnetic field, a freely suspended ferromagnet is expected to undergo pure Larmor precession, a fundamental regime that has not yet been observed in macroscopic particles. Accessing this regime requires a magnetic trap that is sufficiently robust to withstand launch disturbances, yet sufficiently weak and tunable to allow subsequent free evolution. A dedicated magnetic trapping system deployed in the Einstein-Elevator microgravity platform stabilizes a ferromagnetic particle against accelerations up to 1.5 g and enables its controlled release into pure free fall.

Finally, emerging opportunities for high-frequency gravitational-wave detection are discussed in the context of gravitational-wave–electromagnetic coupling and resonant detector concepts. Proposed approaches include a LeMaMa-based magnetic Weber-bar scheme targeting frequencies beyond the current LIGO band, as well as cryogenic microwave-cavity detectors with optimized pickup antennas for GHz and higher-frequency signals (GravNet). Together, these developments point toward a broader sensing program in which levitated magnets and resonant electromagnetic systems enable new searches for weak magnetic fields, inertial effects, and gravitational waves across previously unexplored frequency ranges.