Assembly of a Janus composite nanoparticle optically levitated in vacuum

The optically levitated mechanical system in vacuum is a powerful platform in physics. It has been displaying more extensive application prospects. This paper presents an experimental study of optical levitation, identification, motion measurement, and assembly of two-species photoluminescence nanoparticles. A laser trapping array simultaneously levitates nitrogen-vacancy (NV) nanodiamonds and Yb³⁺/Er³⁺ : NaY F₄ nanoparticles. The species of each nanoparticle can be individually identified by measuring the photoluminescence spectrum. We choose the single NV nanodiamond and Yb³⁺/Er³⁺ : NaY F₄ nanoparticle and assemble them into a Janus composite nanoparticle, which integrates the merits of the two components. This work demonstrates the potential advantages of a hybrid optically levitated system. It provides a practicable scheme for the study of macroscopic quantum phenomena and precision measurement thanks to the spin manipulation or spin-mechanical coupling of a NV diamond and by simultaneously implementing laser refrigeration to the Yb³⁺/Er³⁺ : NaY F₄ nanoparticle in an optically levitated composite nanoparticle.