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A nanoparticle levitated in a vacuum is a promising tool for exploring macroscopic quantum mechanics, precision measurements of forces and non-equilibrium thermodynamics. While cooling the centre-of-mass motion to micro-kelvin temperatures has been achieved, the internal temperature has to date remained at or above room temperature.

In the September 2017 issue of Nature Photonics, Dr A. Rahman and Professor P. Barker from Physics and Astronomy at °×С½ãÂÛ̳ report on the first demonstration of optical refrigeration of a submicrometre particle suspended by laser light. The tiny levitated cryostat, consists of a single nanocrystal of Yb³⁺:YLF crystal cooled to temperatures as cold as −143 °C by illuminating, trapping and aligning it with a single laser beam. Their work has shown that the internal temperature of the nanocrystal can be controlled over a wide range using different trapping laser wavelengths. The laser polarization controls the orientation of the trapped crystal and maximizes its cooling. This development is a further important step towards bringing these macroscopic systems into the quantum regime.

Citation: Laser refrigeration, alignment and rotation of levitated Yb3+:YLF nanocrystals, A.T.M. Anishur Rahman and P. F. Barker, Nature Phonics, Nature Photonics 11, 634-638 (2017)