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 Yb^3+/Er^3+:NaYF_4 nanoparticles. The species of each nanoparticle can be individually identified by measuring the photoluminescence spectrum. We choose the single NV nanodiamond and Yb^3+/Er^3+:NaYF_4 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 an NV diamond and by simultaneously implementing laser refrigeration to the Yb^3+/Er^3+:NaYF_4 nanoparticle in an optically levitated composite nanoparticle.