Macroscopic direct observation of optical spin-dependent lateral forces and left-handed torques

Observing and taming the effects arising from non-trivial light-matter interaction has always triggered scientists to better understand nature and develop photonic technologies. However, despite tremendous conceptual advances(1,2), so far there have been only a few experimental proposals to reveal unusual optomechanical manifestations that are hardly seen in everyday life, such as negative radiation pressure(3,4), transverse forces(5,6) or left-handed torques(7). Here, we report naked-eye identification of spin-dependent lateral displacements of centimetre-sized objects endowed with structured birefringence. Left-handed macroscopic rotational motion is also reported. The unveiled effects ultimately rely on spin-orbit optical interactions and are driven by lateral force fields that are five orders of magnitude larger than those reported previously, as a result of the proposed design. By highlighting the spin-orbit optomechanics of anisotropic and inhomogeneous media, these results allow structured light-matter interaction to move from a scientific curiosity to a new asset for the optical manipulation toolbox.