Determining the Internal Temperature of an Optically Levitated Nanoparticle in Vacuum by Doped- Er3+ -Ion Luminescence

In recent years, optically levitated systems have emerged as an important platform for conducting fundamental physics studies and precision measurements. The internal temperature of the levitated nanoparticles plays a critical role in determining the measuring sensitivity and decoherence of the system. In this study, we perform experiments on the internal temperature of a rare-earth-doped nanoparticle alpha-NaYF4:Yb3+/Er3+ levitated in an intermediate vacuum. To determine the internal temperature of the nanoparticle, we measure the luminescence intensity ratio of the thermally coupled levels of the doped Er(3+ )ions. Our results show that the internal temperature of the optically levitated nanoparticle increases as the air pressure decreases and that there is a coupling between the internal temperature and center-of-mass motion of the nanoparticle levitated in vacuum. We also find a correlation between the slow rise in internal temperature and the abrupt loss of the levitated nanoparticle, which can be used to guide stabilization of the optical trap.