Cooling a nanoparticle in metalens-based optical tweezers

Optical levitation and cooling of nanoparticles in high vacuum offer an exceptional platform for ultrasensitive metrology and sensing. However, conventional optical tweezers rely on bulky objective lenses, limiting their miniaturization and application. Here, we design and fabricate a metalens with a numerical aperture of 0.83, operating at 1064 nm in vacuum, and a diameter of 600 μm. The metalens serves as a compact alternative to objective lenses for laser trapping. With the metalens-based tweezers, we trap a nanoparticle at a minimal pressure of 1.4 × 10^-6 mbar and cool its center-of-mass motion via parametric feedback to around 100 mK. The nanoparticle has been stably trapped for over 30 days. Our work demonstrates stable trapping and cooling of a nanoparticle in ultra-high vacuum using a metalens-based optical tweezers, enabling new opportunities in high-precision miniaturized optomechanical sensing.