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Torque

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Torque is an important quantity for describing the dynamics of a rotating rigid body. We see the application of torque in many ways in the world, such as when pressing the accelerator in a car, which causes the engine to apply additional torque on the drivetrain. Here, we define torque and provide a framework to create an equation to calculate torque for a rigid body with fixed-axis rotation.
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Related Experiment Video

Updated: May 9, 2026

Characterizing Dissipative Elastic Metamaterials Produced by Additive Manufacturing

Characterizing Dissipative Elastic Metamaterials Produced by Additive Manufacturing

Published on: June 28, 2024

Self-induced torque in hyperbolic metamaterials.

Pavel Ginzburg¹, Alexey V Krasavin, Alexander N Poddubny

¹Department of Physics, King's College London, Strand, London WC2R 2LS, United Kingdom. pavel.ginzburg@kcl.ac.uk

Physical Review Letters

|August 6, 2013

Summary

This summary is machine-generated.

Quantum emitters in anisotropic materials generate self-torques, aligning to boost radiation efficiency. This quantum-mechanical effect is significantly enhanced using hyperbolic metamaterials, opening new avenues for optical force applications.

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Area of Science:

Quantum optics and nanophotonics
Materials science and condensed matter physics

Background:

Optical forces are crucial across scientific disciplines, typically requiring intense radiation for observable effects.
Quantum emitters interacting with their environment are fundamental to understanding light-matter interactions.

Purpose of the Study:

To demonstrate and theoretically describe self-induced torques on quantum emitters in anisotropic media.
To investigate the role of material anisotropy in enhancing these self-torques for potential applications.

Main Methods:

Development of a universal quantum-mechanical theory for self-induced torques.
Utilizing the radiation reaction approach and Langevin local quantization of electromagnetic excitations.
Comparison of self-torque enhancement in hyperbolic metamaterials versus conventional anisotropic crystals.

Main Results:

Quantum emitters spontaneously align in anisotropic media to maximize radiation efficiency via self-induced torques.
A more than 2 orders of magnitude enhancement of self-torque was observed in hyperbolic metamaterials.
The observed enhancement stems from the unique hyperbolic dispersion and negative permittivity tensor components.

Conclusions:

Self-induced torques offer a novel mechanism for controlling quantum emitter orientation without external fields.
Anisotropic metamaterials provide a powerful platform for amplifying optical forces and tailoring quantum emitter behavior.
This work paves the way for advanced applications in nanophotonics, quantum technologies, and optical manipulation.