Levitation and controlled MHz rotation of a nanofabricated rod by a high-NA metalens

An optically levitated nanoparticle in a vacuum provides an ideal platform for ultra-precision measurements and fundamental physics studies because of the exceptionally high-quality factor and rich motion modes, which can be engineered by manipulating the optical field and the geometry of the nanoparticle. Nanofabrication technology with the ability to create arbitrary nanostructure arrays offers a precise way of engineering the optical field and the geometry of the nanoparticle. Here, for the first time, we optically levitate and rotate a nanofabricated nanorod via a nanofabricated a-Si metalens which strongly focuses a 1550 nm laser beam with a numerical aperture of 0.953. By manipulating the laser beam's polarization, the levitated nanorod's translation frequencies can be tuned, and the spin rotation mode can be switched on and off. Then, we showed the control of rotational frequency by changing the laser beam's intensity and polarization as well as the air pressure. Finally, a MHz spin rotation frequency of the nanorod is achieved in the experiment. This is the first demonstration of controlled optical spin in a metalens-based compact optical levitation system. Our research holds promise for realizing scalable on-chip integrated optical levitation systems.