Scientists Uncover Hidden Property of Light That Twists Matter Sideways

A new measurement method reveals that light can twist nanoscale objects in unexpected ways.

Light is not just something we see. It can also exert physical forces that push and twist matter. In the 1870s, James Clerk Maxwell proposed that light carries momentum and can apply pressure to objects. Nearly 100 years later, in the 1970s, Arthur Ashkin turned that idea into a practical tool. He created optical tweezers, which use tightly focused laser beams to trap and move extremely small particles.

Even though researchers have long understood that light can apply tiny forces, measuring them has been a major challenge. At the nanoscale, objects are constantly buffeted by thermal motion, which makes these weak forces difficult to detect.

A New Way to Measure Tiny Forces

Scientists at Hokkaido University have now introduced a method that can measure these forces with high precision. Using this approach, they uncovered an unexpected effect: light can cause tiny objects to rotate sideways, perpendicular to the direction the light is traveling.

“We developed a novel measurement platform called the ‘micro-drone,’ which enables, for the first time, full three-dimensional characterization of optical forces and torques acting on nanostructures,” says Professor Yoshito Y. Tanaka of Hokkaido University.

The setup places a nanostructure at the center of a small, cross-shaped device known as a micro-drone. Four laser beams hold the platform steady, similar to optical tweezers gripping its edges. By tracking how the platform shifts and rotates, researchers can determine the forces acting on the object inside.

Overcoming Limitations of Optical Tweezers

“Optical tweezers have been a powerful tool since Arthur Ashkin’s pioneering work, recognized with the Nobel Prize in 2018,” says Tanaka. “Using them, conventional methods could only measure rotation of an object along a single axis. Our approach overcomes this limitation by measuring not the nanostructure itself but the platform containing the nanostructure.”

This technique captures motion and rotation in all directions, providing a full three-dimensional view. It effectively amplifies nanoscale forces by translating them into larger, more measurable movements of the platform.

To test the method, the researchers used tiny gold structures shaped like the letter “V.” When exposed to light inside the micro-drone, these structures displayed a behavior known as transverse optical torque. Instead of rotating along the light’s path, they turned sideways.

“We were able to observe, using the new method, a phenomenon that had not been experimentally observed before: transverse optical torque acting at the nanoscale,” says Tanaka.

Rethinking How Light Interacts With Matter

The origin of this effect was unexpected. Previous theories suggested that such motion would depend on the light’s angular momentum. However, the team found that a different property, called optical helicity, is responsible. This property describes the “handedness” or twist of the light’s electromagnetic field.

The researchers confirmed this by designing experiments that removed angular momentum while preserving helicity. The sideways rotation still occurred, showing that helicity plays the key role.

This finding offers a deeper understanding of how light interacts with matter at extremely small scales. It also points to new ways of controlling nanoscale systems, with possible applications in light-driven nanomachines and advanced sensing technologies.

“This work represents a new measurement paradigm for nanoscale optomechanics,” says Tanaka. “Just as optical tweezers opened a new field in single-molecule biophysics, we hope this platform will unlock access to nanoscale mechanical phenomena that have so far remained beyond reach.”

Reference: “Transverse optical torque observed at the nanoscale” by Ryoma Fukuhara, Tsutomu Shimura and Yoshito Y. Tanaka, 20 April 2026, Nature Physics.
DOI: 10.1038/s41567-026-03268-6

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