Ultrasensitive magnetometry with levitated ferromagnetic torque sensors

Magnetically levitated micro or nano-objects are becoming increasingly attractive, both in the context of quantum science, for instance to probe quantum mechanics in the macroscopic limit, and in ultrasensitive mechanical sensing. The most peculiar feature of these systems is the very high degree of isolation from the environment that can be potentially achieved.  We will discuss an approach based on levitating micromagnets by Meissner effect in a gravitational-superconducting trap, using SQUIDs as motion detectors.  Preliminary measurements show that levitation can be realized in fair agreement with the Meissner effect. Furthermore, ultralow damping rate of rotational and translational modes was demonstrated, down to 10^-5 s^-1, with the ultimate limits yet to be investigated. Several applications of magnetically levitated sensors in fundamental physics can be conceived. Ultrasensitive force or torque sensors can be used, for instance, to test wavefunction-collapse models or to investigate exotic interactions beyond the standard model. More specifically, we will discuss the potential of these systems in ultrasensitive magnetometry. A rotational torque sensor based on a levitated micromagnet is expected to overcome the Standard Quantum Limit on magnetometry, and, in particular, to surpass by orders of magnitude the Energy Resolution Limit, often proposed as a conventional benchmark for ultrasensitive magnetometers. Remarkably, this goal may be achievable not only in the atom-like Larmor precession regime, as initially proposed [1], but also in the more common librational regime [2]. We will discuss the current state of experiments and future prospects.

 

[1] D.F. Jackson Kimball et al., Precessing Ferromagnetic Needle Magnetometer, Phys. Rev. Lett. 116, 190801 (2016).

[2] A. Vinante et al., Surpassing the Energy Resolution Limit with ferromagnetic torque sensors, Phys. Rev. Lett. 127, 070801 (2021).