A Speck of Magnet Floating on Nothing
A speck of metal, roughly the width of a fine human hair, levitates inside a lead cylinder chilled to a few degrees above the coldest temperature the universe allows. Not once a second, not a thousand times a second, but 138 million times every minute. That is the regime researchers have now reached with a levitated microrotor, and the consequences reach from the laboratory bench out toward questions about the nature of gravity and the hidden mass of the cosmos.
The team behind the work placed a spherical magnet, about 30 micrometres across, inside a lead cylinder and cooled the whole assembly with liquid helium to approximately -269 °C. [1] At that temperature lead becomes a superconductor, a material that conducts electricity with no loss and, crucially, pushes magnetic fields out of its interior. The effect has a name: the Meissner effect. A magnet held above a superconductor therefore feels a repulsive push and floats. Enclose the apparatus in a chamber emptied of air, and the floating magnet meets almost no resistance at all.
A magnetic coil then set the sphere spinning, and the numbers that followed are the kind that make a physicist sit up. The rotor exceeded 2.3 megahertz — 138 million revolutions per minute. [1] It is, by the team’s own account, the fastest magnetically levitated rotor demonstrated so far.
What makes the feat more than a curiosity is how little slows it down. The team describes an extremely low damping rate, which would translate into a startling persistence: the spinning speed would take 17 days to fall by half. [1] Tao Wang at the Agency for Science Technology and Research in Singapore frames the achievement in terms of endurance, noting that in how many turns it completes before slowing significantly, the rotor belongs in the same league as the spinning Earth.
The Next Question Is What the Silence Can Hear
The point of a rotor that barely slows is not the speed itself. It is the sensitivity that comes with it. Because the sphere experiences essentially no friction, and because it is both magnetic and cold, its motion reacts to its surroundings with extraordinary sharpness. A whisper of gas, a faint field, a slight torque — each leaves a mark on the rotation that can be read out.
The researchers have already put this to work. Because the rotor experiences essentially no friction, its behaviour is very sensitive to its environment, and the team has already tested it as a gauge of vacuum at very low temperatures. In plainer terms: the spinning sphere works as a vacuum gauge that stays reliable in exactly the cold conditions where quantum computers must operate. Builders of such machines need to know how empty their chambers really are, and they need to know it while everything sits near absolute zero.
Benjamin Stickler at Ulm University in Germany sees a second use: the levitated magnet could precisely sense and measure magnetic fields. Team member Andrea Vinante at the National Research Council in Italy points further out, describing the device as a promising platform for tests of fundamental physics — searches for effects tied to dark matter particles, and sensing of gravitational waves at frequencies so far unexplored. At very low temperatures quantum effects take over, he notes, so the rotor could also probe quantum mechanics and its interplay with gravity at micrometre scales.
That vacuum-gauge capability could serve builders of quantum computers, which often must be kept extremely cold and isolated in order to work.
Why a Slow Spinner Makes a Sharp Sensor
The anchor for all of this is the reported damping figure. Everything else — the 138 million revolutions per minute, the 17-day half-life, the pressure sensing, the fundamental-physics tests — follows from a rotor that loses its motion that slowly. High rotational speed, low temperature and near-zero friction, taken together, make the sphere extraordinarily sensitive to its environment — a promising sensor for extremely weak forces and fields.
The record for the fastest rotating human-made object overall still belongs elsewhere — to a levitated sphere as well, but one nano-sized, invisible to the naked eye, held aloft by laser beams rather than superconductivity. [1] The new rotor is larger and held by a different mechanism. That distinction matters: a sensor that can be built around is a sensor that can be put to work. The work appears in Science Advances. [1].
