Dynamics of a Ferromagnetic Particle Levitated Over a Superconductor

TL;DR

This paper explores the dynamics of levitated ferromagnetic particles above superconductors, demonstrating potential for ultrasensitive torque measurements by analyzing their quasiperiodic motion in magnetic traps.

Contribution

It provides experimental insights into the behavior of ferromagnetic particles levitated over superconductors, highlighting potential for quantum-limited torque sensing.

Findings

Particles are trapped in flux pinning sites on the superconductor

Quasiperiodic motion of particles is characterized optically

Levitation enables near frictionless conditions for torque measurement

Abstract

Under conditions where the angular momentum of a ferromagnetic particle is dominated by intrinsic spin, applied torque is predicted to cause gyroscopic precession of the particle. If the particle is sufficiently isolated from the environment, a measurement of spin precession can potentially yield sensitivity to torque beyond the standard quantum limit. Levitation of a micron-scale ferromagnetic particle above a superconductor is a possible method of near frictionless suspension enabling observation of ferromagnetic particle precession and ultrasensitive torque measurements. We experimentally investigate the dynamics of a micron-scale ferromagnetic particle levitated above a superconducting niobium surface. We find that the levitating particles are trapped in potential minima associated with residual magnetic flux pinned by the superconductor and, using an optical technique, characterize the quasiperiodic motion of the particles in these traps.