Metalens-based optical levitation in vacuum

Optical levitation is a powerful technique for a range of applications including novel sensors and manipulation of quantum signals for precise measurements. However, conventional optical tweezers require a dramatically bulky and high numerical-aperture objective for trapping and an extra condenser lens to collect the scattering light for detection. Here, we show a dielectric planar metalens consisting of 500-nm-thick high-vacuum-compatible silicon nanopillars. The flat metalens has a high numerical aperture of 0.88 at 1064 nm in vacuum. We realize the first metalens-based optical levitation of nanoparticles in vacuum. Due to its flat surface, the scattered light of the trapped particle can directly interfere with the back reflection of the incident beam, making measurement more convenient. We also study the transferring of trapped nanoparticles between two separated optical trapping wells. Optical levitation with an ultrathin metalens in vacuum has the potential to be applied to on-chip sensing and trapping ultracold atoms and molecules.