Ultrasensitive torque detection and ultrafast rotation with an optically levitated nanoparticle

Torque sensors have enabled great accomplishments in physics including the discovery of Coulomb’s law and Cavendish’s first determination of the gravitational constant, and is widely used for studies such as small-scale magnetism and the Casimir effect. Here, we develop an ultrasensitive torque sensor with an optically levitated nanoparticle in vacuum and experimentally demonstrate a torque sensitivity of (4.2 ± 1.2) × 10^-27 Nm / sqrt(Hz) at room temperature [1] without the need of comlex nanofabrication or cryogenic cooling. With the optically levitated particles, we are also able to achieve a record high mechanical rotation exceeding 5 GHz [1,2]. Our calculations suggest our torque sensor will allow detection of vacuum friction near a surface under realistic conditions.

[1] J. Ahn, Z. Xu, J. Bang, P. Ju, X. Gao, T. Li. arXiv:1908.03453
[2] J. Ahn, Z. Xu, J. Bang, Y.-H. Deng, T. M. Hoang, Q. Han, R.-M. Ma, and T. Li, Phys. Rev. Lett. 121, 033603 (2018).