Optically levitated nanoparticles in vacuum have great potentials in precision measurements, thermodynamics and macroscopic quantum mechanics. We have assembled and levitated silica nanodumbbells in high vacuum. With a circularly polarized laser, we have driven them to rotate beyond 1 GHz [J Ahn, et al. Phys. Rev. Lett., 121, 033603 (2018)]. With a linearly-polarized laser, we have observed its torsional vibration. Based on our experimental results, we proposed that this system can be used to study the coupling between the rotation of a nanoparticle and an electron spin [arXiv:1811.01641], and study the Casimir torque due to the angular momentum of quantum vacuum fluctuations [Phys. Rev. A, 96, 033843 (2017)]. With a levitated nanoparticle under drive, we also tested the differential fluctuation theorem and a generalized Jarzynski equality that is valid for arbitrary initial states [Phys. Rev. Lett. 120, 080602 (2018)]. Recently, we investigated the rotation of a levitated nanocluster to deepen our understanding of light-matter interaction.
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