A magnetically levitated conducting rotor with ultra-low rotational damping circumventing eddy loss

Levitation of macroscopic objects in a vacuum is a key step towards the development of high-precision inertial sensors and pressure sensors, as well as towards the fundamental studies of quantum mechanics and its relation to gravity. Diamagnetic levitation offers a passive method at room temperature to isolate macroscopic objects in vacuum environments, yet eddy current damping remains a critical limitation for electrically conductive materials. We show that there are situations where the motion of conductors in magnetic fields does not, in principle, produce eddy damping, and demonstrate an electrically conducting rotor diamagnetically levitated in an axially symmetric magnetic field in high vacuum. Experimental measurements and finite-element simulations reveal gas collision damping as the dominant loss mechanism at high pressures, while residual eddy damping, which arises from symmetry-breaking factors such as platform tilt or material imperfections, dominates at low pressures. The conclusion is supported by an analytic proof and an analytic example of zero steady current density for a rotating conductor in an axially symmetric magnetic field. This demonstrates a macroscopic levitated rotor with extremely low rotational damping and paves the way to fully suppress rotor damping, enabling ultra-low-loss rotors for gyroscopes, pressure sensing, and fundamental physics tests. Levitation of macroscopic objects in a vacuum is crucial for developing innovative inertial and pressure sensors, as well as exploring the relation between quantum mechanics and gravity. Here, the authors demonstrate a conducting rotor diamagnetically levitated in an axially symmetric magnetic field in high vacuum, with minimal rotational damping.