講座內容：An optically levitatednanoparticle in vacuum is aparadigm optomechanical system for sensingandstudying macroscopic quantum mechanics. Whileits center-of-mass motion hasbeen investigated in-tensively, its torsional vibration has only been stud-iedtheoretically in limited cases. Here we re-port the first experimentalobservation of the tor-sional vibration of an optically levitated nonspher-icalnanoparticle in vacuum. We achieve this byutilizing the coupling between thespin angular mo-mentum of photons and the torsional vibration ofa nonsphericalnanoparticle whose polarizability isa tensor. The torsional vibration frequencycanbe one order of magnitude higher than its center-of-mass motion frequency,which is promising forground state cooling. We propose a simple yetnovel schemeto achieve ground state cooling of itstorsional vibration with alinearly-polarized Gaus-sian cavity mode. A levitated nanao-diamondwithbuilding-in Nitrogen-vacancy centers is also suit-able for generatingmultipartite quantum entangle-ment and simulating many-body spins models.Wewill briefly discuss it in the last of the talk.

參考文獻：Phys. Rev. Lett. 117, 123604 (2016), arXiv:1611.05599