Laser refrigeration, alignment and rotation of levitated Yb3+:YLF nanocrystals

The ability to cool and manipulate levitated nanoparticles in vacuum is a promising tool for exploring macroscopic quantum mechanics(1,2), precision measurements of forces(3) and non-equilibrium thermodynamics(4,5). The extreme isolation afforded by optical levitation offers a low-noise, undamped environment that has been used to measure zeptonewton forces(3) and radiation pressure shot noise(6), and to demonstrate centre-of-mass motion cooling(7,8). Ground-state cooling and the creation of macroscopic quantum superpositions are now within reach, but control of both the centre of mass and internal temperature is required. While cooling the centreof- mass motion to micro-kelvin temperatures has now been achieved, the internal temperature has remained at or above room temperature. Here, we realize a nanocryostat by refrigerating levitated Yb3+: YLF nanocrystals to 130 K using antiStokes fluorescence cooling, while simultaneously using the optical trapping field to align the crystal to maximize cooling.