Nanodrone Driven by Symmetry-Selective Light Recoiling.

Abstract

Optical nanomachines offer a versatile platform for performing nanoscale tasks, with the simplest and most fundamental example being the light-driven "nanodrone"─a freely movable particle propelled by light. Although light-driven microdrones have been successfully developed, extending this concept to the nanoscale faces substantial challenges arising from fabrication limits, optical interference, and weakening of optical forces at smaller scales. We introduce a scalable mechanism that overcomes these barriers by exploiting particle symmetry. The approach relies on optical recoil forces, enabling motion controlled entirely by the polarization state of a structureless plane wave. Pressed against a substrate by the incident light, the particle moves freely in the transverse plane as the polarization is varied. Symmetry analysis reveals that particles with D<i>_n</i> symmetry experience no lateral force or axial torque under linear or circular polarization, except for specific values of <i>n</i>. Notably, for D₃-symmetric particles, linear polarization induces a lateral force, while circular polarization generates an axial torque. Using triangular silicon nanopillars, we demonstrate a single-beam, polarization-controlled light-driven nanodrone. This symmetry-based strategy provides robust and scalable control from the micro- to nanoscale, mitigating Brownian fluctuations and fabrication imperfections, and thus holds strong potential for future nanoscale applications.