Topological water-wave structures manipulating particles.

Topological wave structures, such as vortices, polarization textures and skyrmions, appear in various quantum and classical wave fields, including optics and acoustics. In particular, optical vortices have found numerous applications, ranging from quantum information to astrophysics. Furthermore, both optical and acoustic structured waves are crucial in the manipulation of small particles, from atoms to macroscopic biological objects. Recently, there has been a surge of interest in structured water surface waves, which can be notable analogues of quantum, optical and acoustic wave systems. However, topological water-wave forms, especially their ability to manipulate particles, have not yet been demonstrated. Here we describe the controllable generation of topological structures, namely wave vortices, skyrmions and polarization Möbius strips, in gravity water waves. Most importantly, we demonstrate the efficient manipulation of subwavelength and wavelength-order floating particles with topologically structured water waves. This includes trapping the particles in the high-intensity field zones and controlling their orbital and spinning motion due to the orbital and spin angular momenta of the water waves. Our results reveal the water-wave counterpart of optical and acoustic manipulation, which paves the way for applications in hydrodynamics and microfluidics.