A general no-go theorem for loss-free optical torque, and its enantiomer-differential escape route
Year: 2026
Type: preprint
Abstract: We show that an isotropic, lossless dipolar particle, locally embedded in a homogeneous, lossless host, cannot experience axial optical torque under any illumination, in any photonic environment, whatever its own chirality--a general identity extending the sphere-in-free-space result to arbitrary chiral and substrate-coupled environments. Shape anisotropy is the essential escape route, and the resulting torque is not generic: closed-form, radiative-reaction-dressed polarizabilities for a chiral dielectric ellipsoid show its loss-free "optical spanner" torque changing by an order of magnitude between enantiomers (κ\to -κ), a mechanical response impossible for any sphere. Above a high-index or lossy substrate like gold or silicon, standing-wave enhancement, or simply a larger particle at a near-contact gap, brings it beyond optical-torque-wrench thresholds.
Source: arXiv (Cornell University)
Authors: Ren, Juanjuan, Gordon, Reuven, Hughes, Stephen
Institutions: Queen's University, University of Victoria
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7214294682