A general no-go theorem for loss-free optical torque, and its enantiomer-differential escape route
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.
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BibTeX
@misc{ren2026general,
title = {{A general no-go theorem for loss-free optical torque, and its enantiomer-differential escape route}},
author = {Juanjuan Ren and Reuven Gordon and Stephen Hughes},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.28696},
eprint = {2609.28696},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.28696},
}
RIS
TY - UNPB
TI - A general no-go theorem for loss-free optical torque, and its enantiomer-differential escape route
AU - Juanjuan Ren
AU - Reuven Gordon
AU - Stephen Hughes
PY - 2026
DA - 2026/09/23
PB - arXiv
DO - 10.48550/arxiv.2609.28696
UR - https://arxiv.org/abs/2609.28696
AB - 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.
ER -