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 centre-of-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 anti-Stokes fluorescence cooling, while simultaneously using the optical trapping field to align the crystal to maximize cooling. A nanocryostat is realized through the refrigeration of levitated Yb3+:YLF nanocrystals to 130 K using anti-Stokes fluorescence cooling, while the laser polarization allows orientation control of the trapped nanocrystal and maximizes its cooling.