Ultrasensitive torque detection and 5D cooling of optically levitated nanoparticles*

The rotational degrees of freedom of a levitated nanoparticle have drawn growing interest as promising platforms for torque sensing and rotational quantum mechanics. Here, we demonstrate the state-of-art torque sensor reaching sensitivity of (4.2 ± 1.2) ×10^-27 N m Hz^-1/2 at room temperature with an optically levitated nanorotor in vacuum [1]. Our calculations show that this system can be used to detect the long-sought vacuum friction near a surface. We also drive a levitated nanodumbbell to rotate at a record high speed beyond 5 GHz, which has potential application for studying the quantum geometric phase. Moreover, we perform the first five-dimensional cooling for a levitated nanodumbbell with motional temperature reduced by 2 orders from room temperature [2]. This experiment paves the way towards the Casimir toque detection near a birefringent surface [3] and full quantum control of a levitated non-spherical particle.

[1] J. Ahn, Z. Xu, J. Bang, P. Ju et al. Nat. Nanotechnol. 15, 89 (2020)
[2] J. Bang, T. Seberson, P. Ju et al. Phys. Rev. Research 2, 043054 (2020)
[3] Z. Xu and T. Li, Phys. Rev. A 96, 033843 (2017)