  Optical levitation of dielectric particles in vacuum is a powerful technique
for precision measurements, testing fundamental physics, and quantum
information science. Conventional optical tweezers require bulky optical
components for trapping and detection. Here we design and fabricate an
ultrathin dielectric metalens with a high numerical aperture of 0.88 at 1064 nm
in vacuum. It consists of 500 nm-thick silicon nano-antennas, which are
compatible with ultrahigh vacuum. We demonstrate optical levitation of
nanoparticles in vacuum with a single metalens. The trapping frequency can be
tuned by changing the laser power and polarization. We also transfer a
levitated nanoparticle between two separated optical tweezers. Optical
levitation with an ultrathin metalens in vacuum provides opportunities for a
wide range of applications including on-chip sensing. Such metalenses will also
be useful for trapping ultacold atoms and molecules.
