In recent years, various systems for trapping and cooling the center of mass of levitated nanoparticles have been explored. This is of interest not only for the study of fundamental physics in quantum systems but also due to the potential for developing contact-free cooling methods for condensed matter systems.
In this work, we present the progress made in trapping and cooling Yb³⁺:NaYF₄ nanoparticles with diameters between 100 and 200 nm using an electric feedback method, as well as subsequent fluorescence experiments that allow us to measure the internal temperature of the nanoparticles and test laser cooling protocols for the internal degrees of freedom of the crystal.
These cooling protocols exploit the coupling between the electronic transitions of Yb³⁺ dopants and the phonon modes of the host crystal. A tunable laser, aligned to the anti-Stokes region of the spectrum, is utilized to drive transitions that produce a net extraction of thermal energy from the crystal.
These experiments are part of a broader theoretical investigation conducted by our research group into anti-Stokes cooling protocols, which aim to surpass the current cooling limits established for these systems, as well as to explore alternative systems for overcoming such limits.