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Freely levitating rotor spins out ultraprecise sensors for classical and quantum physics

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  Published in Science and Technology on Friday, October 10th 2025 at 5:57 GMT by Phys.org
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Freely Leviting Rotor Ushers in Ultra‑Precise Sensors

A team of physicists has unveiled a miniature rotor that levitates in a magnetic field, free from any mechanical contact with its support structure. This innovation—presented at a recent symposium in Geneva—promises to push the limits of sensitivity for a new generation of inertial sensors, magnetic gradiometers, and even fundamental‑physics experiments that require an exquisitely quiet reference frame.

The Problem of Friction in High‑Precision Sensing

For decades, the performance of many precision instruments has been capped by the unavoidable friction between a moving part and its mounting. “Every tiny bit of drag or wobble translates into noise,” explains Dr. Marta Liu, the project’s lead investigator from the University of California, Berkeley. “When you’re trying to measure something as delicate as a micro‑Newton force or a nanoradian rotation, even microscopic losses in a bearing can drown out the signal.” Traditional air bearings or magnetic levitation systems either require large vacuum chambers or sophisticated cryogenic environments, both of which add bulk and complexity to sensor designs.

The new rotor addresses this by combining two proven technologies—superconducting magnetic bearings and active feedback control—in a way that was previously thought impossible. The rotor is a lightweight, 2‑mm‑diameter disk made from a high‑purity titanium alloy. It is suspended 30 µm above a stack of permanent magnets arranged in a Halbach array. Because the magnets are magnetized in a carefully engineered pattern, the rotor is held in a stable, self‑aligned position without any external support. A superconducting ring surrounds the rotor and, when cooled below its critical temperature with liquid helium, generates a magnetic flux that locks the rotor’s position with picometer precision.

Active Feedback and Ultra‑Low Noise

Even with the superconducting lock in place, the rotor can still wobble if left uncontrolled. The researchers employ an array of optical interferometers that monitor the rotor’s position and angular orientation in real time. These signals feed back to a set of piezoelectric actuators that apply minute corrective forces to the magnetic field. The net result is a rotor that remains fixed to a single micro‑degree of misalignment over timescales of hours—an improvement by more than an order of magnitude over the best non‑contact bearings reported in the literature (see the linked Nature Physics paper on magnetic levitation).

Because the rotor does not touch any physical bearing, the mechanical quality factor (Q) climbs from the typical 10,000–50,000 range for conventional gyroscopes to an astonishing 10^7. In a Q factor of 10^7, the rotor can store angular momentum for days before losing 1 % of it, a level that translates into torque sensitivities below 10^−18 Nm. Such performance has immediate implications for gravitational‑wave detectors, where the ability to sense minute changes in spacetime curvature depends on measuring displacements smaller than a fraction of a proton diameter.

Applications in Inertial Navigation and Beyond

The first practical application the team is targeting is high‑precision inertial navigation for small autonomous drones. Current MEMS gyroscopes suffer from drift over minutes, whereas the levitated rotor can maintain a stable heading over hours without requiring a GPS reference. “We’re envisioning a chip‑scale inertial measurement unit that’s light enough to fit in a 1‑gram payload but has the stability of a laboratory‑grade gyroscope,” says Dr. Liu.

Beyond navigation, the sensor’s sensitivity opens doors for geophysics and geodesy. By measuring the subtle torque induced by Earth’s magnetic field variations, the device could contribute to mapping subsurface mineral deposits. Moreover, the rotor’s extreme isolation makes it an attractive platform for testing the equivalence principle and searching for new physics, such as fifth‑force interactions that might manifest as anomalous torques at sub‑millimeter distances.

Commercializing the Levitation Advantage

While the laboratory prototype demonstrates the principle, the team is now collaborating with industrial partners to miniaturize the system. The biggest hurdle is scaling the cooling infrastructure. The current cryostat uses liquid helium, but the researchers are exploring high‑temperature superconductors that would allow operation at 20–30 K using a simple closed‑cycle refrigerator. “If we can eliminate the helium altogether, we’ll have a path to mass production,” notes project engineer Rahul Singh, who works at the National Institute of Standards and Technology (NIST).

An early commercial version could reach market within five years, targeting defense, aerospace, and scientific research sectors that require ultraprecise attitude control. Meanwhile, the open‑source community is already looking at the data‑analysis software the team released, which makes it easier to extract torque signals from the interferometric readouts.

Looking Forward

The freely levitating rotor is a striking example of how careful engineering can push the frontiers of measurement. By removing friction entirely, the researchers have unlocked a level of sensitivity that was once the domain of massive interferometers. As the technology matures, it may become a standard component in any system that demands precise, drift‑free orientation and force measurement—an exciting development for both applied engineering and fundamental physics alike.