Related Experiment Video
Updated: Oct 15, 2025

Magnetic Tweezers for the Measurement of Twist and Torque
Published on: May 19, 2014
Characterization of a double torsion pendulum used to detect spin-induced torque based on Beth's experiment
Runa Yasuda1, Atsushi Hatakeyama1
1Department of Applied Physics, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan.
Abstract:
We characterized a double torsion pendulum system, including measurements of the photon-spin-induced torque. Our experimental strategy was similar to that used in Beth's experiment, which was performed in 1936 to measure photon-spin-induced torque using forced oscillation caused by polarization modulation of light incident on a suspended object. Through simple passive isolation of the suspended object from external vibration noise, the achieved torque sensitivity was 2 × 10-17 N m in a measurement time of 104 s, which is close to the thermal noise limit and one order smaller than the minimum torque measured in Beth's experiment. The observed spin-induced torque exerted on the light-absorbing optics is consistent with the angular momentum transfer of ℏ per photon.
Related Concept Videos
Torsional Pendulum
As long as the rigid body's angular displacement is small, its oscillation can be modeled as a linear angular oscillation. The amplitude of the oscillation is an angle. The role of mass is played...
Simple Pendulum
The period of a simple pendulum depends on two factors: its length and the acceleration due to gravity. The period is completely independent of any other factors, such as mass or maximum displacement. For small displacements, a pendulum...
Physical Pendulum
When dealing with complicated systems, the mass moment of inertia is an important parameter, as it...
Forced Oscillations
Angle of Twist: Problem Solving
Torque Free Motion

