An optically levitated nanoparticle in a vacuum is excellent for precision measurements. We have optically levitated silica nanodumbbells in a vacuum and driven them to rotate beyond 5 GHz. With an optically levitated nanorotor, we demonstrated a torque sensor with a record-high sensitivity [Nature Nanotechnology, 15, 89 (2020)]. Recently, we designed and fabricated an ultrathin metalens with a high numerical aperture (NA=0.88) and used it to levitate a nanoparticle in a vacuum [Optica, 8, 1359 (2021)]. Such a system will provide opportunities for on-chip sensing. In addition, we have trapped a nanodumbbell near a surface with a separation of less than one micrometer, and used it to demonstrate an optically levitated scanning probe microscope beyond the diffraction limit. Our work will be important for studying quantum surface interactions.
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